Please note: double dashed longoptions (e.g. --version) 
are written this way: --

Two resp. three consecutive dashes simply result in a 
long resp. extra long dash.

Architecture specific stuff (like memory models, code 
examples) should maybe later go

into seperate sections/chapters/appendices (it is hard 
to document PIC or Z80 in 

a 8051 centered document) - for now simply add.

SDCC Compiler User Guide

SDCC 2.5.6
$Date: 2006-04-24 13:29:10 -0700 (Mon, 24 Apr 2006) $ 
$Revision: 4121 $

The above strings enclosed in $ are automatically 
updated by Subversion

Table of Contents

Introduction
    About SDCC
    Open Source
    Typographic conventions
    Compatibility with previous versions
    System Requirements
    Other Resources
    Wishes for the future
Installing SDCC
    Configure Options
    Install paths
    Search Paths
    Building SDCC
        Building SDCC on Linux
        Building SDCC on OSX 2.x
        Cross compiling SDCC on Linux for Windows
        Building SDCC on Windows 
        Building SDCC using Cygwin and Mingw32
        Building SDCC Using Microsoft Visual C++ 6.0/NET (MSVC)
        Building SDCC Using Borland
        Windows Install Using a ZIP Package
        Windows Install Using the Setup Program
        VPATH feature
    Building the Documentation
    Reading the Documentation
    Testing the SDCC Compiler
    Install Trouble-shooting
        If SDCC does not build correctly
        What the ./configure does
        What the make does
        What the make install command does.
    Components of SDCC
        sdcc - The Compiler
        sdcpp - The C-Preprocessor
        asxxxx, aslink, link-xxx - The Assemblers and Linkage Editors
        s51 - The Simulator
        sdcdb - Source Level Debugger
Using SDCC
    Compiling
        Single Source File Projects
        Projects with Multiple Source Files
        Projects with Additional Libraries
        Using sdcclib to Create and Manage Libraries
    Command Line Options
        Processor Selection Options
        Preprocessor Options
        Linker Options
        MCS51 Options
        DS390 / DS400 Options
        Z80 Options
        Optimization Options
        Other Options
        Intermediate Dump Options
        Redirecting output on Windows Shells
    Environment variables
    Storage Class Language Extensions
        MCS51/DS390 Storage Class Language Extensions
            data / near
            xdata / far
            idata
            pdata
            code
            bit
            sfr / sfr16 / sfr32 / sbit
            Pointers to MCS51/DS390 specific memory spaces
            Notes on MCS51 memory layout
        Z80/Z180 Storage Class Language Extensions
            sfr (in/out to 8-bit addresses)
            banked sfr (in/out to 16-bit addresses)
            sfr (in0/out0 to 8 bit addresses on Z180/HD64180)
        HC08 Storage Class Language Extensions
            data 
            xdata 
    Absolute Addressing
    Parameters & Local Variables
    Overlaying
    Interrupt Service Routines
        General Information
        MCS51/DS390 Interrupt Service Routines
        HC08 Interrupt Service Routines
        Z80 Interrupt Service Routines
    Enabling and Disabling Interrupts
        Critical Functions and Critical Statements
        Enabling and Disabling Interrupts directly
        Semaphore locking (mcs51/ds390)
    Functions using private register banks (mcs51/ds390)
    Startup Code
        MCS51/DS390 Startup Code
        HC08 Startup Code
        Z80 Startup Code
    Inline Assembler Code
        A Step by Step Introduction
        Naked Functions
        Use of Labels within Inline Assembler
    Interfacing with Assembler Code
        Global Registers used for Parameter Passing
        Assembler Routine (non-reentrant)
        Assembler Routine (reentrant)
    int (16 bit) and long (32 bit) Support
    Floating Point Support
    Library Routines
        Compiler support routines (_gptrget, _mulint etc.)
        Stdclib functions (puts, printf, strcat etc.)
            <stdio.h>
        Math functions (sin, pow, sqrt etc.)
        Other libraries
    Memory Models
        MCS51 Memory Models
            Small, Medium and Large
            External Stack
        DS390 Memory Model
    Pragmas
    Defines Created by the Compiler
Notes on supported Processors
    MCS51 variants
        pdata access by SFR 
        Other Features available by SFR
    DS400 port
    The Z80 and gbz80 port
    The HC08 port
    The PIC14 port
        C code and 14bit PIC code page and RAM banks
        Creating a device include file 
        Interrupt code
        Linking and assembling
        Command-line options
        The library
            error: missing definition for symbol __gptrget1
            Processor mismatch in file XXX.
        Known bugs
            initialized data
    The PIC16 port
        Global Options
        Port Specific Options
            General Options
            Optimization Options
            Linking Options
            Debugging Options
        Enviromental Variables
        Preprocessor Macros
        Directories
        Pragmas
        Header Files
        Libraries
        Memory Models
        Stack
        Functions
        Function return values
        Interrupts
        Generic Pointers
        PIC16 C Libraries
            Standard I/O Streams
            Printing functions
            Signals
        PIC16 Port -- Tips
            Stack size
Debugging with SDCDB 
    Compiling for Debugging
    How the Debugger Works
    Starting the Debugger
    Command Line Options
    Debugger Commands
    Interfacing with DDD
    Interfacing with XEmacs
TIPS
    Tools included in the distribution
    Documentation included in the distribution
    Related open source tools
    Related documentation / recommended reading
    Some Questions
Support
    Reporting Bugs
    Requesting Features
    Submitting patches
    Getting Help
    ChangeLog
    Release policy
    Examples
    Quality control
    Use of SDCC in Education
SDCC Technical Data
    Optimizations
        Sub-expression Elimination
        Dead-Code Elimination
        Copy-Propagation
        Loop Optimizations
        Loop Reversing
        Algebraic Simplifications
        'switch' Statements
        Bit-shifting Operations.
        Bit-rotation
        Nibble and Byte Swapping
        Highest Order Bit / Any Order Bit
        Higher Order Byte / Higher Order Word
        Peephole Optimizer
    ANSI-Compliance
    Cyclomatic Complexity
    Retargetting for other Processors
Compiler internals
    The anatomy of the compiler
    A few words about basic block successors, predecessors and dominators
Acknowledgments



Introduction

 About SDCC

SDCC (Small Device C Compiler) is an open source, 
retargettable, optimizing ANSI-C compiler by Sandeep 
Dutta designed for 8 bit Microprocessors. The current 
version targets Intel MCS51 based Microprocessors 
(8031, 8032, 8051, 8052, etc.), Dallas DS80C390 
variants, Freescale (formerly Motorola) HC08 and Zilog 
Z80 based MCUs. It can be retargetted for other 
microprocessors, support for Microchip PIC, Atmel AVR 
is under development. The entire source code for the 
compiler is distributed under GPL. SDCC uses ASXXXX & ASLINK
, an open source retargettable assembler & linker. SDCC 
has extensive language extensions suitable for 
utilizing various microcontrollers and underlying 
hardware effectively. 

In addition to the MCU specific optimizations SDCC also 
does a host of standard optimizations like:

 global sub expression elimination, 

 loop optimizations (loop invariant, strength reduction 
  of induction variables and loop reversing), 

 constant folding & propagation, 

 copy propagation, 

 dead code elimination 

 jump tables for switch statements.

For the back-end SDCC uses a global register allocation 
scheme which should be well suited for other 8 bit 
MCUs. 

The peep hole optimizer uses a rule based substitution 
mechanism which is MCU independent. 

Supported data-types are:

 char (8 bits, 1 byte), 

 short and int (16 bits, 2 bytes), 

 long (32 bit, 4 bytes)

 float (4 byte IEEE). 

The compiler also allows inline assembler code to be 
embedded anywhere in a function. In addition, routines 
developed in assembly can also be called.

SDCC also provides an option (--cyclomatic) to report 
the relative complexity of a function. These functions 
can then be further optimized, or hand coded in 
assembly if needed. 

SDCC also comes with a companion source level debugger 
SDCDB, the debugger currently uses ucSim a freeware 
simulator for 8051 and other micro-controllers. SDCDB 
and ucSim are currently not available on Win32 
platforms. 

The latest version can be downloaded from [http://sdcc.sourceforge.net/snap.php]. Please 
note: the compiler will probably always be some steps 
ahead of this documentationObviously this has pros and cons.

 Open Source

All packages used in this compiler system are open 
source and freeware; source code for all the 
sub-packages (pre-processor, assemblers, linkers etc) 
is distributed with the package. This documentation is 
maintained using a freeware word processor (LyX).
This program is free software; you can redistribute it 
and/or modify it under the terms of the GNU General 
Public License as published by the Free Software 
Foundation; either version 2, or (at your option) any 
later version. This program is distributed in the hope 
that it will be useful, but WITHOUT ANY WARRANTY; 
without even the implied warranty of MERCHANTABILITY or 
FITNESS FOR A PARTICULAR PURPOSE. See the GNU General 
Public License for more details. You should have 
received a copy of the GNU General Public License along 
with this program; if not, write to the Free Software 
Foundation, 59 Temple Place - Suite 330, Boston, MA 
02111-1307, USA. In other words, you are welcome to 
use, share and improve this program. You are forbidden 
to forbid anyone else to use, share and improve what 
you give them. Help stamp out software-hoarding! 

 Typographic conventions

Throughout this manual, we will use the following 
convention. Commands you have to type in are printed in 
"sans serif". Code samples are printed in typewriter 
font. Interesting items and new terms are printed in italic.

 Compatibility with previous versions

This version has numerous bug fixes compared with the 
previous version. But we also introduced some 
incompatibilities with older versions. Not just for the 
fun of it, but to make the compiler more stable, 
efficient and ANSI compliant (see section [sub:ANSI-Compliance] for 
ANSI-Compliance). 


 short is now equivalent to int (16 bits), it used to 
  be equivalent to char (8 bits) which is not ANSI compliant.

 the default directory for gcc-builds where include, 
  library and documentation files are stored is now in 
  /usr/local/share.

 char type parameters to vararg functions are casted to 
  int unless explicitly casted, e.g.: 
    char a=3;
    printf ("%d %c\n", a, (char)a);
   will push a as an int and as a char resp.

 option --regextend has been removed.

 option --noregparms has been removed.

 option --stack-after-data has been removed.

 bit and sbit types now consistently behave like the 
  C99 _Bool type with respect to type conversion. The 
  most common incompatibility resulting from this 
  change is related to bit toggling idioms, e.g.:
    bit b;
    b = ~b; /* equivalent to b=1 instead of toggling b */
    b = !b; /* toggles b */
  In previous versions, both forms would have toggled 
  the bit.

<pending: more incompatibilities?>

 System Requirements

What do you need before you start installation of SDCC? 
A computer, and a desire to compute. The preferred 
method of installation is to compile SDCC from source 
using GNU gcc and make. For Windows some pre-compiled 
binary distributions are available for your 
convenience. You should have some experience with 
command line tools and compiler use.

 Other Resources

The SDCC home page at [http://sdcc.sourceforge.net/] is a great place to find 
distribution sets. You can also find links to the user 
mailing lists that offer help or discuss SDCC with 
other SDCC users. Web links to other SDCC related sites 
can also be found here. This document can be found in 
the DOC directory of the source package as a text or 
HTML file. A pdf version of this document is available 
at [http://sdcc.sourceforge.net/doc/sdccman.pdf]. Some of the other tools (simulator and assembler) 
included with SDCC contain their own documentation and 
can be found in the source distribution. If you want 
the latest unreleased software, the complete source 
package is available directly from Subversion on 
https://svn.sourceforge.net/svnroot/sdcc/trunk/sdcc.

 Wishes for the future

There are (and always will be) some things that could 
be done. Here are some I can think of:


char KernelFunction3(char p) at 0x340;


better code banking support for mcs51

If you can think of some more, please see the section [sub:Requesting-Features] 
about filing feature requests.


Installing SDCC

For most users it is sufficient to skip to either 
section [sub:Building-SDCC-on-Linux] or section [sub:Windows-Install]. More detailled instructions 
follow below.

 Configure Options

The install paths, search paths and other options are 
defined when running 'configure'. The defaults can be 
overridden by:

--prefix see table below

--exec_prefix see table below

--bindir see table below

--datadir see table below

docdir environment variable, see table below

include_dir_suffix environment variable, see table below

lib_dir_suffix environment variable, see table below

sdccconf_h_dir_separator environment variable, either / 
or \\ makes sense here. This character will only be 
used in sdccconf.h; don't forget it's a C-header, 
therefore a double-backslash is needed there.

--disable-mcs51-port Excludes the Intel mcs51 port

--disable-gbz80-port Excludes the Gameboy gbz80 port

--disable-z80-port Excludes the z80 port

--disable-avr-port Excludes the AVR port

--disable-ds390-port Excludes the DS390 port

--disable-hc08-port Excludes the HC08 port

--disable-pic-port Excludes the PIC port

--disable-xa51-port Excludes the XA51 port

--disable-ucsim Disables configuring and building of ucsim

--disable-device-lib Disables automatically building 
device libraries

--disable-packihx Disables building packihx

--enable-doc Build pdf, html and txt files from the lyx sources

--enable-libgc Use the Bohem memory allocator. Lower 
runtime footprint.

Furthermore the environment variables CC, CFLAGS, ... 
the tools and their arguments can be influenced. Please 
see `configure --help` and the man/info pages of 
`configure` for details.

The names of the standard libraries STD_LIB, 
STD_INT_LIB, STD_LONG_LIB, STD_FP_LIB, STD_DS390_LIB, 
STD_XA51_LIB and the environment variables 
SDCC_DIR_NAME, SDCC_INCLUDE_NAME, SDCC_LIB_NAME are 
defined by `configure` too. At the moment it's not 
possible to change the default settings (it was simply 
never required).

These configure options are compiled into the binaries, 
and can only be changed by rerunning 'configure' and 
recompiling SDCC. The configure options are written in 
italics to distinguish them from run time environment 
variables (see section search paths).

The settings for "Win32 builds" are used by the SDCC team 
to build the official Win32 binaries. The SDCC team 
uses Mingw32 to build the official Windows binaries, 
because it's

 open source, 

 a gcc compiler and last but not least

 the binaries can be built by cross compiling on 
  Sourceforge's compile farm.

See the examples, how to pass the Win32 settings to 
'configure'. The other Win32 builds using Borland, VC 
or whatever don't use 'configure', but a header file 
sdcc_vc_in.h is the same as sdccconf.h built by 
'configure' for Win32.

These defaults are:


+---------------------+--------------------+-----------------+
| Variable            | default            | Win32 builds    |
+---------------------+--------------------+-----------------+
+---------------------+--------------------+-----------------+
| PREFIX              | /usr/local         | \sdcc           |
+---------------------+--------------------+-----------------+
| EXEC_PREFIX         | $PREFIX            | $PREFIX         |
+---------------------+--------------------+-----------------+
| BINDIR              | $EXECPREFIX/bin    | $EXECPREFIX\bin |
+---------------------+--------------------+-----------------+
| DATADIR             | $PREFIX/share      | $PREFIX         |
+---------------------+--------------------+-----------------+
| DOCDIR              | $DATADIR/sdcc/doc  | $DATADIR\doc    |
+---------------------+--------------------+-----------------+
| INCLUDE_DIR_SUFFIX  | sdcc/include       | include         |
+---------------------+--------------------+-----------------+
| LIB_DIR_SUFFIX      | sdcc/lib           | lib             |
+---------------------+--------------------+-----------------+



'configure' also computes relative paths. This is 
needed for full relocatability of a binary package and 
to complete search paths (see section search paths below):
 

+----------------------+-------------+--------------+
| Variable (computed)  | default     | Win32 builds |
+----------------------+-------------+--------------+
+----------------------+-------------+--------------+
| BIN2DATA_DIR         | ../share    | ..           |
+----------------------+-------------+--------------+
| PREFIX2BIN_DIR       | bin         | bin          |
+----------------------+-------------+--------------+
| PREFIX2DATA_DIR      | share/sdcc  |              |
+----------------------+-------------+--------------+



Examples:

./configure
./configure --prefix="/usr/bin" --datadir="/usr/share"
./configure --disable-avr-port --disable-xa51-port

To cross compile on linux for Mingw32 (see also 
'sdcc/support/scripts/sdcc_mingw32'):

./configure \
CC="i586-mingw32msvc-gcc" CXX="i586-mingw32msvc-g++" \ 
RANLIB="i586-mingw32msvc-ranlib" \
STRIP="i586-mingw32msvc-strip" \
--prefix="/sdcc" \
--datadir="/sdcc" \
docdir="/sdcc/doc" \
include_dir_suffix="include" \
lib_dir_suffix="lib" \
sdccconf_h_dir_separator="\\\\" \
--disable-device-lib\
--disable-ucsim\
--host=i586-mingw32msvc --build=unknown-unknown-linux-gnu

To "cross"compile on Cygwin for Mingw32 (see also 
sdcc/support/scripts/sdcc_cygwin_mingw32):

./configure -C \
CFLAGS="-mno-cygwin -O2" \
LDFLAGS="-mno-cygwin" \
--prefix="/sdcc" \
--datadir="/sdcc" \
docdir="/sdcc/doc" \ 
include_dir_suffix="include" \
lib_dir_suffix="lib" \
sdccconf_h_dir_separator="\\\\" \
--disable-ucsim

'configure' is quite slow on Cygwin (at least on 
windows before Win2000/XP). The option '--C' turns on 
caching, which gives a little bit extra speed. However 
if options are changed, it can be necessary to delete 
the config.cache file.

 Install paths<sub:Install-paths>

+-----------------+--------------------------------+--------------------------------+---------------+
|  Description    |             Path               |            Default             | Win32 builds  |
+-----------------+--------------------------------+--------------------------------+---------------+
+-----------------+--------------------------------+--------------------------------+---------------+
| Binary files*   |         $EXEC_PREFIX           |        /usr/local/bin          |   \sdcc\bin   |
+-----------------+--------------------------------+--------------------------------+---------------+
| Include files   | $DATADIR/ $INCLUDE_DIR_SUFFIX  | /usr/local/share/sdcc/include  | \sdcc\include |
+-----------------+--------------------------------+--------------------------------+---------------+
| Library file**  |   $DATADIR/$LIB_DIR_SUFFIX     |   /usr/local/share/sdcc/lib    |   \sdcc\lib   |
+-----------------+--------------------------------+--------------------------------+---------------+
| Documentation   |            $DOCDIR             |   /usr/local/share/sdcc/doc    |   \sdcc\doc   |
+-----------------+--------------------------------+--------------------------------+---------------+


*compiler, preprocessor, assembler, and linker
**the model is auto-appended by the compiler, e.g. 
small, large, z80, ds390 etc

The install paths can still be changed during `make 
install` with e.g.:

make install prefix=$(HOME)/local/sdcc

Of course this doesn't change the search paths compiled 
into the binaries.

Moreover the install path can be changed by defining DESTDIR:

make install DESTDIR=$(HOME)/sdcc.rpm/

Please note that DESTDIR must have a trailing slash!

 Search Paths<sub:Search-Paths>

Some search paths or parts of them are determined by 
configure variables (in italics, see section above). 
Further search paths are determined by environment 
variables during runtime. 
The paths searched when running the compiler are as 
follows (the first catch wins):

1. Binary files (preprocessor, assembler and linker)


+---------------------------------+------------------+-----------------+
| Search path                     | default          | Win32 builds    |
+---------------------------------+------------------+-----------------+
+---------------------------------+------------------+-----------------+
| $SDCC_HOME/$PPREFIX2BIN_DIR     | $SDCC_HOME/bin   | $SDCC_HOME\bin  |
+---------------------------------+------------------+-----------------+
| Path of argv[0] (if available)  | Path of argv[0]  | Path of argv[0] |
+---------------------------------+------------------+-----------------+
| $PATH                           | $PATH            | $PATH           |
+---------------------------------+------------------+-----------------+
 


2. Include files


+--------------------------------------------------+----------------------------------------------------------------------+--------------------------+
| Search path                                      | default                                                              | Win32 builds             |
+--------------------------------------------------+----------------------------------------------------------------------+--------------------------+
+--------------------------------------------------+----------------------------------------------------------------------+--------------------------+
| --I dir                                          | --I dir                                                              | --I dir                  |
+--------------------------------------------------+----------------------------------------------------------------------+--------------------------+
| $SDCC_INCLUDE                                    | $SDCC_INCLUDE                                                        | $SDCC_INCLUDE            |
+--------------------------------------------------+----------------------------------------------------------------------+--------------------------+
| $SDCC_HOME/$PREFIX2DATA_DIR/$INCLUDE_DIR_SUFFIX  | $SDCC_ HOME/share/sdcc/include                                       | $SDCC_HOME\include       |
+--------------------------------------------------+----------------------------------------------------------------------+--------------------------+
| path(argv[0])/$BIN2DATADIR/$INCLUDE_DIR_SUFFIX   |                                       path(argv[0])/../sdcc/include  | path(argv[0])\..\include |
+--------------------------------------------------+----------------------------------------------------------------------+--------------------------+
| $DATADIR/$INCLUDE_DIR_SUFFIX                     | /usr/local/share/sdcc/include                                        | (not on Win32)           |
+--------------------------------------------------+----------------------------------------------------------------------+--------------------------+
 


The option --nostdinc disables the last two search paths.

3. Library files 


With the exception of "--L dir" the model is 
auto-appended by the compiler (e.g. small, large, z80, 
ds390 etc.). 


+------------------------------------------------------+---------------------------------------------------------------------------+-----------------------------------------------------------------+
| Search path                                          | default                                                                   | Win32 builds                                                    |
+------------------------------------------------------+---------------------------------------------------------------------------+-----------------------------------------------------------------+
+------------------------------------------------------+---------------------------------------------------------------------------+-----------------------------------------------------------------+
| --L dir                                              | --L dir                                                                   | --L dir                                                         |
+------------------------------------------------------+---------------------------------------------------------------------------+-----------------------------------------------------------------+
| $SDCC_LIB/<model>                                    | $SDCC_LIB/<model>                                                         | $SDCC_LIB\<model>                                               |
+------------------------------------------------------+---------------------------------------------------------------------------+-----------------------------------------------------------------+
| $SDCC_HOME/$PREFIX2DATA_DIR/$LIB_DIR_SUFFIX/<model>  | $SDCC_HOME/share/sdcc/lib/<model>                                         | $SDCC_HOME\lib\<model>                                          |
+------------------------------------------------------+---------------------------------------------------------------------------+-----------------------------------------------------------------+
| path(argv[0])/$BIN2DATADIR/$LIB_DIR_SUFFIX/<model>   |                                        path(argv[0])/../sdcc/lib/<model>  |                                    path(argv[0])\..\lib\<model> |
+------------------------------------------------------+---------------------------------------------------------------------------+-----------------------------------------------------------------+
| $DATADIR/$LIB_DIR_SUFFIX/<model>                     | /usr/local/share/sdcc/lib/<model>                                         | (not on Win32)                                                  |
+------------------------------------------------------+---------------------------------------------------------------------------+-----------------------------------------------------------------+



Don't delete any of the stray spaces in the table above 
without checking the HTML output (last line)!

 
The option --nostdlib disables the last two search paths.

 Building SDCC

 Building SDCC on Linux<sub:Building-SDCC-on-Linux>

 Download the source package either from the SDCC 
  Subversion repository or from the nightly snapshots, 
  it will be named something like sdcc.src.tar.gz [http://sdcc.sourceforge.net/snap.php].

 Bring up a command line terminal, such as xterm.

 Unpack the file using a command like: "tar -xvzf 
  sdcc.src.tar.gz", this will create a sub-directory 
  called sdcc with all of the sources.

 Change directory into the main SDCC directory, for 
  example type: "cd sdcc".

 Type "./configure". This configures the package for 
  compilation on your system.

 Type "make". All of the source packages will compile, 
  this can take a while.

 Type "make install" as root. This copies the binary 
  executables, the include files, the libraries and the 
  documentation to the install directories. Proceed 
  with section [sec:Testing-the-SDCC].

 Building SDCC on OSX 2.x

Follow the instruction for Linux.

On OSX 2.x it was reported, that the default gcc 
(version 3.1 20020420 (prerelease)) fails to compile 
SDCC. Fortunately there's also gcc 2.9.x installed, 
which works fine. This compiler can be selected by 
running 'configure' with:

./configure CC=gcc2 CXX=g++2

 Cross compiling SDCC on Linux for Windows

With the Mingw32 gcc cross compiler it's easy to 
compile SDCC for Win32. See section 'Configure Options'.

 Building SDCC on Windows 

With the exception of Cygwin the SDCC binaries uCsim 
and sdcdb can't be built on Windows. They use 
Unix-sockets, which are not available on Win32.

 Building SDCC using Cygwin and Mingw32

For building and installing a Cygwin executable follow 
the instructions for Linux.

On Cygwin a "native" Win32-binary can be built, which 
will not need the Cygwin-DLL. For the necessary 
'configure' options see section 'configure options' or 
the script 'sdcc/support/scripts/sdcc_cygwin_mingw32'.

In order to install Cygwin on Windows download 
setup.exe from [http://www.cygwin.com/||www.cygwin.com]. Run it, set the "default text file type" 
to "unix" and download/install at least the following 
packages. Some packages are selected by default, others 
will be automatically selected because of dependencies 
with the manually selected packages. Never deselect 
these packages!

 flex

 bison

 gcc ; version 3.x is fine, no need to use the old 2.9x

 binutils ; selected with gcc

 make

 rxvt ; a nice console, which makes life much easier 
  under windoze (see below)

 man ; not really needed for building SDCC, but you'll 
  miss it sooner or later

 less ; not really needed for building SDCC, but you'll 
  miss it sooner or later

 svn ; only if you use Subversion access

If you want to develop something you'll need:

 python ; for the regression tests

 gdb ; the gnu debugger, together with the nice GUI "insight"

 openssh ; to access the CF or commit changes

 autoconf and autoconf-devel ; if you want to fight 
  with 'configure', don't use autoconf-stable!

rxvt is a nice console with history. Replace in your 
cygwin.bat the line

bash --login -i 

with (one line):

rxvt -sl 1000 -fn "Lucida Console-12" -sr -cr red

     -bg black -fg white -geometry 100x65 -e bash --login

Text selected with the mouse is automatically copied to 
the clipboard, pasting works with shift-insert.

The other good tip is to make sure you have no 
//c/-style paths anywhere, use /cygdrive/c/ instead. 
Using // invokes a network lookup which is very slow. 
If you think "cygdrive" is too long, you can change it 
with e.g.

mount -s -u -c /mnt

SDCC sources use the unix line ending LF. Life is much 
easier, if you store the source tree on a drive which 
is mounted in binary mode. And use an editor which can 
handle LF-only line endings. Make sure not to commit 
files with windows line endings. The tabulator spacing 
used in the project is 8. Although a tabulator spacing 
of 8 is a sensible choice for programmers (it's a power 
of 2 and allows to display 8/16 bit signed variables 
without loosing columns) the plan is to move towards 
using only spaces in the source.

 Building SDCC Using Microsoft Visual C++ 6.0/NET (MSVC)

Download the source package either from the SDCC 
Subversion repository or from the [http://sdcc.sourceforge.net/snap.php||nightly snapshots], it will be named 
something like sdcc.src.tgz. SDCC is distributed with 
all the projects, workspaces, and files you need to 
build it using Visual C++ 6.0/NET (except for sdcdb.exe 
which currently doesn't build under MSVC). The 
workspace name is 'sdcc.dsw'. Please note that as it is 
now, all the executables are created in a folder called 
sdcc\bin_vc. Once built you need to copy the 
executables from sdcc\bin_vc to sdcc\bin before running 
SDCC. 

WARNING: Visual studio is very picky with line 
terminations; it expects the 0x0d, 0x0a DOS style line 
endings, not the 0x0a Unix style line endings. When 
using the Subversion repository it's easiest to 
configure the svn client to convert automatically for 
you. If however you are getting a message such as "This 
makefile was not generated by Developer Studio etc. etc."
 when opening the sdcc.dsw workspace or any of the 
*.dsp projects, then you need to convert the Unix style 
line endings to DOS style line endings. To do so you 
can use the "unix2dos" utility freely available on the 
internet. Doug Hawkins reported in the sdcc-user list 
that this works:

C:\Programming\SDCC> unix2dos sdcc.dsw
C:\Programming\SDCC> for /R %I in (*.dsp) do @unix2dos "%I"

In order to build SDCC with MSVC you need win32 
executables of bison.exe, flex.exe, and gawk.exe. One 
good place to get them is [http://unxutils.sourceforge.net||here]

Download the file UnxUtils.zip. Now you have to install 
the utilities and setup MSVC so it can locate the 
required programs. Here there are two alternatives 
(choose one!):

 The easy way:
  
  a) Extract UnxUtils.zip to your C:\ hard disk 
  PRESERVING the original paths, otherwise bison won't 
  work. (If you are using WinZip make certain that 'Use 
  folder names' is selected)
  
  b) In the Visual C++ IDE click Tools, Options, select 
  the Directory tab, in 'Show directories for:' select 
  'Executable files', and in the directories window add 
  a new path: 'C:\user\local\wbin', click ok.
  
  (As a side effect, you get a bunch of Unix utilities 
  that could be useful, such as diff and patch.)

 A more compact way:
  
  This one avoids extracting a bunch of files you may 
  not use, but requires some extra work:
  
  a) Create a directory were to put the tools needed, 
  or use a directory already present. Say for example 'C:\util'.
  
  b) Extract 'bison.exe', 'bison.hairy', 
  'bison.simple', 'flex.exe', and gawk.exe to such 
  directory WITHOUT preserving the original paths. (If 
  you are using WinZip make certain that 'Use folder 
  names' is not selected)
  
  c) Rename bison.exe to '_bison.exe'.
  
  d) Create a batch file 'bison.bat' in 'C:\util\' and 
  add these lines: 
    set BISON_SIMPLE=C:\util\bison.simple 
    set BISON_HAIRY=C:\util\bison.hairy
    _bison %1 %2 %3 %4 %5 %6 %7 %8 %9
  
  Steps 'c' and 'd' are needed because bison requires 
  by default that the files 'bison.simple' and 
  'bison.hairy' reside in some weird Unix directory, 
  '/usr/local/share/' I think. So it is necessary to 
  tell bison where those files are located if they are 
  not in such directory. That is the function of the 
  environment variables BISON_SIMPLE and BISON_HAIRY.
  
  e) In the Visual C++ IDE click Tools, Options, select 
  the Directory tab, in 'Show directories for:' select 
  'Executable files', and in the directories window add 
  a new path: 'c:\util', click ok. Note that you can 
  use any other path instead of 'c:\util', even the 
  path where the Visual C++ tools are, probably: 
  'C:\Program Files\Microsoft Visual 
  Studio\Common\Tools'. So you don't have to execute 
  step 'e' :)

That is it. Open 'sdcc.dsw' in Visual Studio, click 
'build all', when it finishes copy the executables from 
sdcc\bin_vc to sdcc\bin, and you can compile using SDCC.

 Building SDCC Using Borland

 From the sdcc directory, run the command "make -f 
  Makefile.bcc". This should regenerate all the .exe 
  files in the bin directory except for sdcdb.exe 
  (which currently doesn't build under Borland C++).

 If you modify any source files and need to rebuild, be 
  aware that the dependencies may not be correctly 
  calculated. The safest option is to delete all .obj 
  files and run the build again. From a Cygwin BASH 
  prompt, this can easily be done with the command (be 
  sure you are in the sdcc directory):
  
  find . \( -name '*.obj' -o -name '*.lib' -o -name 
  '*.rul' \) -print -exec rm {} \;
  
  or on Windows NT/2000/XP from the command prompt with 
  the command:
  
  del /s *.obj *.lib *.rul from the sdcc directory.

 Windows Install Using a ZIP Package

 Download the binary zip package from [http://sdcc.sf.net/snap.php] and unpack it 
  using your favorite unpacking tool (gunzip, WinZip, 
  etc). This should unpack to a group of 
  sub-directories. An example directory structure after 
  unpacking the mingw32 package is: c:\sdcc\bin for the 
  executables, c:\sdcc\include and c:\sdcc\lib for the 
  include and libraries.

 Adjust your environment variable PATH to include the 
  location of the bin directory or start sdcc using the 
  full path.

 Windows Install Using the Setup Program<sub:Windows-Install>

Download the setup program sdcc-x.y.z-setup.exe for an 
official release from 
[http://sf.net/project/showfiles.php?group_id=599] or a setup program for one of the snapshots 
sdcc_yyyymmdd_setup.exe from [http://sdcc.sf.net/snap.php] and execute it. A windows 
typical installer will guide you through the 
installation process.

 VPATH feature

SDCC supports the VPATH feature provided by configure 
and make. It allows to separate the source and build 
trees. Here's an example:

cd ~                     # cd $HOME

tar -xzf sdcc.src.tar.gz # extract source to directory sdcc

mkdir sdcc.build         # put output in sdcc.build

cd sdcc.build

../sdcc/configure        # configure is doing all the magic!

make

That's it! configure will create the directory tree 
will all the necessary Makefiles in ~/sdcc.build. It 
automagically computes the variables srcdir, top_srcdir 
and top_buildir for each directory. After running make 
the generated files will be in ~/sdcc.build, while the 
source files stay in ~/sdcc.
This is not only usefull for building different 
binaries, e.g. when cross compiling. It also gives you 
a much better overview in the source tree when all the 
generated files are not scattered between the source 
files. And the best thing is: if you want to change a 
file you can leave the original file untouched in the 
source directory. Simply copy it to the build 
directory, edit it, enter `make clean`, `rm 
Makefile.dep` and `make`. make will do the rest for you!

 Building the Documentation

Add --enable-doc to the configure arguments to build 
the documentation together with all the other stuff. 
You will need several tools (LyX, LaTeX, LaTeX2HTML, 
pdflatex, dvipdf, dvips and makeindex) to get the job 
done. Another possibility is to change to the doc 
directory and to type "make" there. You're invited to 
make changes and additions to this manual 
(sdcc/doc/sdccman.lyx). Using LyX [http://www.lyx.org] as editor is 
straightforward. Prebuilt documentation in html and pdf 
format is available from [http://sdcc.sf.net/snap.php].

 Reading the Documentation

Currently reading the document in pdf format is 
recommended, as for unknown reason the hyperlinks are 
working there whereas in the html version they are notIf you should know why please drop us a note. 
You'll find the pdf version at [http://sdcc.sf.net/doc/sdccman.pdf]. 
A html version should be online at [http://sdcc.sf.net/doc/sdccman.html/index.html].
This documentation is in some aspects different from a 
commercial documentation: 

 It tries to document SDCC for several processor 
  architectures in one document (commercially these 
  probably would be separate documents/products). This document
   currently matches SDCC for mcs51 and DS390 best and 
  does give too few information about f.e. Z80, PIC14, 
  PIC16 and HC08.

 There are many references pointing away from this 
  documentation. Don't let this distract you. If there 
  f.e. was a reference like [http://www.opencores.org] together with a statement "
  some processors which are targetted by SDCC can be 
  implemented in a field programmable gate array" or [http://sf.net/projects/fpgac] "
  have you ever heard of an open source compiler that 
  compiles a subset of C for an FPGA?" we expect you to 
  have a quick look there and come back. If you read 
  this you are on the right track.

 Some sections attribute more space to problems, 
  restrictions and warnings than to the solution.

 The installation section and the section about the 
  debugger is intimidating.

 There are still lots of typos and there are more 
  different writing styles than pictures.

 Testing the SDCC Compiler<sec:Testing-the-SDCC>

The first thing you should do after installing your 
SDCC compiler is to see if it runs. Type "sdcc --version"
 at the prompt, and the program should run and tell you 
the version. If it doesn't run, or gives a message 
about not finding sdcc program, then you need to check 
over your installation. Make sure that the sdcc bin 
directory is in your executable search path defined by 
the PATH environment setting (see section [sub:Install-Trouble-shooting] Install 
trouble-shooting for suggestions). Make sure that the 
sdcc program is in the bin folder, if not perhaps 
something did not install correctly.

SDCC is commonly installed as described in section "
Install and search paths".

Make sure the compiler works on a very simple example. 
Type in the following test.c program using your 
favorite ASCII editor:

char test;

void main(void) {
    test=0;
}

Compile this using the following command: "sdcc -c 
test.c". If all goes well, the compiler will generate a 
test.asm and test.rel file. Congratulations, you've 
just compiled your first program with SDCC. We used the 
-c option to tell SDCC not to link the generated code, 
just to keep things simple for this step.

The next step is to try it with the linker. Type in 
"sdcc test.c". If all goes well the compiler will link 
with the libraries and produce a test.ihx output file. 
If this step fails (no test.ihx, and the linker 
generates warnings), then the problem is most likely 
that SDCC cannot find the /usr/local/share/sdcc/lib 
directory (see section [sub:Install-Trouble-shooting] Install trouble-shooting for suggestions).

The final test is to ensure SDCC can use the standard 
header files and libraries. Edit test.c and change it 
to the following:

#include <string.h>

char str1[10];

void main(void) {
  strcpy(str1, "testing");
}

Compile this by typing "sdcc test.c". This should 
generate a test.ihx output file, and it should give no 
warnings such as not finding the string.h file. If it 
cannot find the string.h file, then the problem is that 
SDCC cannot find the /usr/local/share/sdcc/include 
directory (see the section [sub:Install-Trouble-shooting] Install trouble-shooting 
section for suggestions). Use option --print-search-dirs
 to find exactly where SDCC is looking for the include 
and lib files.

 Install Trouble-shooting<sub:Install-Trouble-shooting>

 If SDCC does not build correctly

A thing to try is starting from scratch by unpacking 
the .tgz source package again in an empty directory. 
Configure it like:

./configure 2>&1 | tee configure.log

and build it like:

make 2>&1 | tee make.log

If anything goes wrong, you can review the log files to 
locate the problem. Or a relevant part of this can be 
attached to an email that could be helpful when 
requesting help from the mailing list.

 What the "./configure" does

The "./configure" command is a script that analyzes your 
system and performs some configuration to ensure the 
source package compiles on your system. It will take a 
few minutes to run, and will compile a few tests to 
determine what compiler features are installed.

 What the "make" does

This runs the GNU make tool, which automatically 
compiles all the source packages into the final 
installed binary executables.

 What the "make install" command does.

This will install the compiler, other executables 
libraries and include files into the appropriate 
directories. See sections [sub:Install-paths], [sub:Search-Paths] about install and search paths.
On most systems you will need super-user privileges to 
do this.

 Components of SDCC

SDCC is not just a compiler, but a collection of tools 
by various developers. These include linkers, 
assemblers, simulators and other components. Here is a 
summary of some of the components. Note that the 
included simulator and assembler have separate 
documentation which you can find in the source package 
in their respective directories. As SDCC grows to 
include support for other processors, other packages 
from various developers are included and may have their 
own sets of documentation.

You might want to look at the files which are installed 
in <installdir>. At the time of this writing, we find 
the following programs for gcc-builds:
 
In <installdir>/bin:

 sdcc - The compiler.

 sdcpp - The C preprocessor.

 asx8051 - The assembler for 8051 type processors.

 as-z80, as-gbz80 - The Z80 and GameBoy Z80 assemblers.

 aslink -The linker for 8051 type processors.

 link-z80, link-gbz80 - The Z80 and GameBoy Z80 linkers.

 s51 - The ucSim 8051 simulator. Not available on Win32 
  platforms.

 sdcdb - The source debugger. Not available on Win32 platforms.

 packihx - A tool to pack (compress) Intel hex files.

In <installdir>/share/sdcc/include

 the include files

In <installdir>/share/sdcc/lib

 the subdirs src and small, large, z80, gbz80 and ds390 
  with the precompiled relocatables.

In <installdir>/share/sdcc/doc

 the documentation

As development for other processors proceeds, this list 
will expand to include executables to support 
processors like AVR, PIC, etc.

 sdcc - The Compiler

This is the actual compiler, it in turn uses the 
c-preprocessor and invokes the assembler and linkage editor.

 sdcpp - The C-Preprocessor

The preprocessor is a modified version of the GNU 
preprocessor. The C preprocessor is used to pull in 
#include sources, process #ifdef statements, #defines 
and so on.

 asxxxx, aslink, link-xxx - The Assemblers and Linkage Editors

This is retargettable assembler & linkage editor, it 
was developed by Alan Baldwin. John Hartman created the 
version for 8051, and I (Sandeep) have made some 
enhancements and bug fixes for it to work properly with SDCC.

 s51 - The Simulator

S51 is a freeware, opensource simulator developed by 
Daniel Drotos. The simulator is built as part of the 
build process. For more information visit Daniel's web 
site at: [http://mazsola.iit.uni-miskolc.hu/~drdani/embedded/s51]. It currently supports the core mcs51, the 
Dallas DS80C390 and the Phillips XA51 family. S51 is 
currently not available on Win32 platfors.

 sdcdb - Source Level Debugger

Sdcdb is the companion source level debugger. More 
about sdcdb in section [cha:Debugging-with-SDCDB]. The current version of the 
debugger uses Daniel's Simulator S51, but can be easily 
changed to use other simulators. Sdcdb is currently not 
available on Win32 platfors.

Using SDCC

 Compiling

 Single Source File Projects

For single source file 8051 projects the process is 
very simple. Compile your programs with the following 
command "sdcc sourcefile.c". This will compile, 
assemble and link your source file. Output files are as follows:

 sourcefile.asm - Assembler source file created by the compiler

 sourcefile.lst - Assembler listing file created by the Assembler

 sourcefile.rst - Assembler listing file updated with 
  linkedit information, created by linkage editor

 sourcefile.sym - symbol listing for the sourcefile, 
  created by the assembler

 sourcefile.rel or sourcefile.o - Object file created 
  by the assembler, input to Linkage editor

 sourcefile.map - The memory map for the load module, 
  created by the Linker

 sourcefile.mem - A file with a summary of the memory usage

 sourcefile.ihx - The load module in Intel hex format 
  (you can select the Motorola S19 format with --out-fmt-s19
  . If you need another format you might want to use objdump
   or srecord). Both formats are documented in the 
  documentation of srecord

 sourcefile.adb - An intermediate file containing debug 
  information needed to create the .cdb file (with --debug
  ) 

 sourcefile.cdb - An optional file (with --debug) 
  containing debug information. The format is 
  documented in cdbfileformat.pdf

 sourcefile. - (no extension) An optional AOMF or AOMF51
   file containing debug information (generated with 
  option --debug). The (Intel) absolute object module 
  format is commonly used by third party tools (debuggers
  , simulators, emulators)

 sourcefile.dump* - Dump file to debug the compiler it 
  self (generated with option --dumpall) (see section [sub:Intermediate-Dump-Options]  
  and section [sub:The-anatomy-of] "Anatomy of the compiler").

 Projects with Multiple Source Files

SDCC can compile only ONE file at a time. Let us for 
example assume that you have a project containing the 
following files:

foo1.c (contains some functions)
foo2.c (contains some more functions)
foomain.c (contains more functions and the function main)

The first two files will need to be compiled separately 
with the commands: 

sdcc -c foo1.c
sdcc -c foo2.c

Then compile the source file containing the main() 
function and link the files together with the following 
command: 

sdcc foomain.c foo1.rel foo2.rel

Alternatively, foomain.c can be separately compiled as 
well: 

sdcc -c foomain.c
sdcc foomain.rel foo1.rel foo2.rel

The file containing the main() function must be the 
first file specified in the command line, since the 
linkage editor processes file in the order they are 
presented to it. The linker is invoked from SDCC using 
a script file with extension .lnk. You can view this 
file to troubleshoot linking problems such as those 
arising from missing libraries.

 Projects with Additional Libraries

Some reusable routines may be compiled into a library, 
see the documentation for the assembler and linkage 
editor (which are in <installdir>/share/sdcc/doc) for 
how to create a .lib library file. Libraries created in 
this manner can be included in the command line. Make 
sure you include the -L <library-path> option to tell 
the linker where to look for these files if they are 
not in the current directory. Here is an example, 
assuming you have the source file foomain.c and a 
library foolib.lib in the directory mylib (if that is 
not the same as your current project):

sdcc foomain.c foolib.lib -L mylib

Note here that mylib must be an absolute path name.

The most efficient way to use libraries is to keep 
separate modules in separate source files. The lib file 
now should name all the modules.rel files. For an 
example see the standard library file libsdcc.lib in 
the directory <installdir>/share/lib/small.

 Using sdcclib to Create and Manage Libraries

Alternatively, instead of having a .rel file for each 
entry on the library file as described in the preceding 
section, sdcclib can be used to embed all the modules 
belonging to such library in the library file itself. 
This results in a larger library file, but it greatly 
reduces the number of disk files accessed by the 
linker.  Additionally, the packed library file contains 
an index of all include modules and symbols that 
significantly speeds up the linking process. To display 
a list of options supported by sdcclib type:


sdcclib -?

To create a new library file, start by compiling all 
the required modules. For example:


sdcc -c _divsint.c

sdcc -c _divuint.c

sdcc -c _modsint.c

sdcc -c _moduint.c

sdcc -c _mulint.c


This will create files _divsint.rel, _divuint.rel, 
_modsint.rel, _moduint.rel, and _mulint.rel. The next 
step is to add the .rel files to the library file:


sdcclib libint.lib _divsint.rel

sdcclib libint.lib _divuint.rel

sdcclib libint.lib _modsint.rel

sdcclib libint.lib _moduint.rel

sdcclib libint.lib _mulint.rel


If the file already exists in the library, it will be 
replaced. To see what modules and symbols are included 
in the library, options -s and -m are available. For example:

sdcclib -s libint.lib
_divsint.rel:

__divsint_a_1_1

__divsint_PARM_2

__divsint
_divuint.rel:

__divuint_a_1_1

__divuint_PARM_2

__divuint_reste_1_1

__divuint_count_1_1

__divuint
_modsint.rel:

__modsint_a_1_1

__modsint_PARM_2

__modsint
_moduint.rel:

__moduint_a_1_1

__moduint_PARM_2

__moduint_count_1_1

__moduint
_mulint.rel:

__mulint_PARM_2

__mulint


If the source files are compiled using --debug, the 
corresponding debug information file .adb will be 
include in the library file as well. The library files 
created with sdcclib are plain text files, so they can 
be viewed with a text editor. It is not recomended to 
modify a library file created with sdcclib using a text 
editor, as there are file indexes numbers located 
accross the file used by the linker to quickly locate 
the required module to link. Once a .rel file (as well 
as a .adb file) is added to a library using sdcclib, it 
can be safely deleted, since all the information 
required for linking is embedded in the library file 
itself. Library files created using sdcclib are used as 
described in the preceding sections.

 Command Line Options

 Processor Selection Options

-mmcs51 Generate code for the Intel MCS51 family of 
processors. This is the default processor target.

-mds390 Generate code for the Dallas DS80C390 processor.

-mds400 Generate code for the Dallas DS80C400 processor.

-mhc08 Generate code for the Freescale/Motorola HC08 
family of processors.

-mz80 Generate code for the Zilog Z80 family of processors.

-mgbz80 Generate code for the GameBoy Z80 processor 
(Not actively maintained).

-mavr Generate code for the Atmel AVR processor (In 
development, not complete). AVR users should probably 
have a look at winavr [http://sourceforge.net/projects/winavr] or [http://www.avrfreaks.net/index.php?name=PNphpBB2&file=index].

I think it is fair to direct users there for now. Open 
source is also about avoiding unnecessary work . But I 
didn't find the 'official' link.

-mpic14 Generate code for the Microchip PIC 14-bit 
processors (p16f84 and variants. In development, not complete).

p16f627 p16f628 p16f84 p16f873 p16f877?

-mpic16 Generate code for the Microchip PIC 16-bit 
processors (p18f452 and variants. In development, not complete).

-mtlcs900h Generate code for the Toshiba TLCS-900H 
processor (Not maintained, not complete).

-mxa51 Generate code for the Phillips XA51 processor 
(Not maintained, not complete).

 Preprocessor Options

-I<path> The additional location where the pre 
processor will look for <..h> or "..h" files.

-D<macro[=value]> Command line definition of macros. 
Passed to the preprocessor.

-M Tell the preprocessor to output a rule suitable for 
make describing the dependencies of each object file. 
For each source file, the preprocessor outputs one 
make-rule whose target is the object file name for that 
source file and whose dependencies are all the files 
`#include'd in it. This rule may be a single line or 
may be continued with `\'-newline if it is long. The 
list of rules is printed on standard output instead of 
the preprocessed C program. `-M' implies `-E'.

-C Tell the preprocessor not to discard comments. Used 
with the `-E' option.

-MM Like `-M' but the output mentions only the user 
header files included with `#include "file"'. System 
header files included with `#include <file>' are omitted.

-Aquestion(answer) Assert the answer answer for 
question, in case it is tested with a preprocessor 
conditional such as `#if #question(answer)'. `-A-' 
disables the standard assertions that normally describe 
the target machine.

-Umacro Undefine macro macro. `-U' options are 
evaluated after all `-D' options, but before any 
`-include' and `-imacros' options.

-dM Tell the preprocessor to output only a list of the 
macro definitions that are in effect at the end of 
preprocessing. Used with the `-E' option.

-dD Tell the preprocessor to pass all macro definitions 
into the output, in their proper sequence in the rest 
of the output.

-dN Like `-dD' except that the macro arguments and 
contents are omitted. Only `#define name' is included 
in the output.

-Wp preprocessorOption[,preprocessorOption]... Pass the 
preprocessorOption to the preprocessor sdcpp. SDCC uses 
an adapted version of the preprocessor cpp of the GNU 
Compiler Collection (gcc), if you need more dedicated 
options please refer to the documentation at [http://www.gnu.org/software/gcc/onlinedocs/].

 Linker Options

-L --lib-path <absolute path to additional libraries> 
This option is passed to the linkage editor's 
additional libraries search path. The path name must be 
absolute. Additional library files may be specified in 
the command line. See section Compiling programs for 
more details.

--xram-loc <Value> The start location of the external ram
, default value is 0. The value entered can be in 
Hexadecimal or Decimal format, e.g.: --xram-loc 0x8000 
or --xram-loc 32768.

--code-loc <Value> The start location of the code 
segment, default value 0. Note when this option is used 
the interrupt vector table is also relocated to the 
given address. The value entered can be in Hexadecimal 
or Decimal format, e.g.: --code-loc 0x8000 or -
-code-loc 32768.

--stack-loc <Value> By default the stack is placed after 
the data segment. Using this option the stack can be 
placed anywhere in the internal memory space of the 
8051. The value entered can be in Hexadecimal or 
Decimal format, e.g. --stack-loc 0x20 or --stack-loc 
32. Since the sp register is incremented before a push 
or call, the initial sp will be set to one byte prior 
the provided value. The provided value should not 
overlap any other memory areas such as used register 
banks or the data segment and with enough space for the 
current application. The --pack-iram  option (which is 
now a default setting) will override this setting, so 
you should also specify the --no-pack-iram  option if 
you need to manually place the stack.

--xstack-loc <Value> By default the external stack is 
placed after the pdata segment. Using this option the 
xstack can be placed anywhere in the external memory 
space of the 8051. The value entered can be in 
Hexadecimal or Decimal format, e.g. --xstack-loc 0x8000 
or --stack-loc 32768. The provided value should not 
overlap any other memory areas such as the pdata or 
xdata segment and with enough space for the current application.

--data-loc <Value> The start location of the internal 
ram data segment. The value entered can be in 
Hexadecimal or Decimal format, eg. --data-loc 0x20 or -
-data-loc 32. (By default, the start location of the 
internal ram data segment  is set as low as possible in 
memory, taking into account the used register banks and 
the bit segment at address 0x20. For example if 
register banks 0 and 1 are used without bit variables, 
the data segment will be set, if --data-loc is not 
used, to location 0x10.)

--idata-loc <Value> The start location of the indirectly 
addressable internal ram of the 8051, default value is 
0x80. The value entered can be in Hexadecimal or 
Decimal format, eg. --idata-loc 0x88 or --idata-loc 136.

--bit-loc <Value> The start location of the bit 
addressable internal ram of the 8051. This is not 
implemented yet. Instead an option can be passed 
directly to the linker: -Wl -bBSEG=<Value>.

--out-fmt-ihx The linker output (final object code) is 
in Intel Hex format. This is the default option. The 
format itself is documented in the documentation of srecord.

--out-fmt-s19 The linker output (final object code) is 
in Motorola S19 format. The format itself is documented 
in the documentation of srecord.

--out-fmt-elf The linker output (final object code) is 
in ELF format. (Currently only supported for the HC08 processors)

-Wl linkOption[,linkOption]... Pass the linkOption to 
the linker. See file sdcc/as/doc/asxhtm.html for more 
on linker options.

 MCS51 Options

--model-small Generate code for Small Model programs, 
see section Memory Models for more details. This is the 
default model.

--model-medium Generate code for Medium model programs, 
see section Memory Models for more details. If this 
option is used all source files in the project have to 
be compiled with this option. It must also be used when 
invoking the linker.

--model-large Generate code for Large model programs, 
see section Memory Models for more details. If this 
option is used all source files in the project have to 
be compiled with this option. It must also be used when 
invoking the linker.

--xstack Uses a pseudo stack in the first 256 bytes in 
the external ram for allocating variables and passing 
parameters. See section [sub:External-Stack]  External Stack for more details.

--iram-size <Value> Causes the linker to check if the 
internal ram usage is within limits of the given value.

--xram-size <Value> Causes the linker to check if the 
external ram usage is within limits of the given value.

--code-size <Value> Causes the linker to check if the 
code memory usage is within limits of the given value.

--stack-size <Value> Causes the linker to check if there 
is at minimum <Value> bytes for stack.

--pack-iram  Causes the linker to use unused register 
banks for data variables and pack data, idata and stack 
together. This is the default now.

--no-pack-iram  Causes the linker to use old style for 
allocating memory areas.

 DS390 / DS400 Options

--model-flat24 Generate 24-bit flat mode code. This is 
the one and only that the ds390 code generator supports 
right now and is default when using -mds390. See 
section Memory Models for more details.

--protect-sp-update disable interrupts during ESP:SP updates.

--stack-10bit Generate code for the 10 bit stack mode 
of the Dallas DS80C390 part. This is the one and only 
that the ds390 code generator supports right now and is 
default when using -mds390. In this mode, the stack is 
located in the lower 1K of the internal RAM, which is 
mapped to 0x400000. Note that the support is 
incomplete, since it still uses a single byte as the 
stack pointer. This means that only the lower 256 bytes 
of the potential 1K stack space will actually be used. 
However, this does allow you to reclaim the precious 
256 bytes of low RAM for use for the DATA and IDATA 
segments. The compiler will not generate any code to 
put the processor into 10 bit stack mode. It is 
important to ensure that the processor is in this mode 
before calling any re-entrant functions compiled with 
this option. In principle, this should work with the --stack-auto
 option, but that has not been tested. It is 
incompatible with the --xstack option. It also only 
makes sense if the processor is in 24 bit contiguous 
addressing mode (see the --model-flat24 option).

--stack-probe insert call to function __stack_probe at 
each function prologue.

--tini-libid <nnnn> LibraryID used in -mTININative. 

--use-accelerator generate code for DS390 Arithmetic 
Accelerator. 

 Z80 Options

--callee-saves-bc Force a called function to always 
save BC.

--no-std-crt0 When linking, skip the standard crt0.o 
object file. You must provide your own crt0.o for your 
system when linking. 

 Optimization Options

--nogcse Will not do global subexpression elimination, 
this option may be used when the compiler creates 
undesirably large stack/data spaces to store compiler 
temporaries (spill locations, sloc). A warning message 
will be generated when this happens and the compiler 
will indicate the number of extra bytes it allocated. 
It is recommended that this option NOT be used, #pragma nogcse
 can be used to turn off global subexpression elimination
 for a given function only.

--noinvariant Will not do loop invariant optimizations, 
this may be turned off for reasons explained for the 
previous option. For more details of loop optimizations 
performed see Loop Invariants in section [sub:Loop-Optimizations]. It is 
recommended that this option NOT be used, #pragma noinvariant
 can be used to turn off invariant optimizations for a 
given function only.

--noinduction Will not do loop induction optimizations, 
see section strength reduction for more details. It is 
recommended that this option is NOT used, #pragma noinduction
 can be used to turn off induction optimizations for a 
given function only.

--nojtbound  Will not generate boundary condition check 
when switch statements are implemented using 
jump-tables. See section [sub:'switch'-Statements] Switch Statements for more 
details. It is recommended that this option is NOT 
used, #pragma nojtbound can be used to turn off boundary 
checking for jump tables for a given function only.

--noloopreverse Will not do loop reversal optimization.

--nolabelopt Will not optimize labels (makes the 
dumpfiles more readable).

--no-xinit-opt Will not memcpy initialized data from 
code space into xdata space. This saves a few bytes in 
code space if you don't have initialized data.

--nooverlay  The compiler will not overlay parameters 
and local variables of any function, see section 
Parameters and local variables for more details.

--no-peep Disable peep-hole optimization with built-in rules.

--peep-file <filename> This option can be used to use 
additional rules to be used by the peep hole optimizer. 
See section [sub:Peephole-Optimizer] Peep Hole optimizations for details on how 
to write these rules.

--peep-asm Pass the inline assembler code through the 
peep hole optimizer. This can cause unexpected changes 
to inline assembler code, please go through the 
peephole optimizer rules defined in the source file 
tree '<target>/peeph.def' before using this option.

--opt-code-speed The compiler will optimize code 
generation towards fast code, possibly at the expense 
of code size.

--opt-code-size The compiler will optimize code 
generation towards compact code, possibly at the 
expense of code speed.

 Other Options

-c --compile-only will compile and assemble the source, 
but will not call the linkage editor.

--c1mode reads the preprocessed source from standard 
input and compiles it. The file name for the assembler 
output must be specified using the -o option.

-E Run only the C preprocessor. Preprocess all the C 
source files specified and output the results to 
standard output.

-o <path/file> The output path resp. file where 
everything will be placed. If the parameter is a path, 
it must have a trailing slash (or backslash for the 
Windows binaries) to be recognized as a path. 

--stack-auto All functions in the source file will be 
compiled as reentrant, i.e. the parameters and local 
variables will be allocated on the stack. See section [sec:Parameters-and-Local-Variables] 
Parameters and Local Variables for more details. If 
this option is used all source files in the project 
should be compiled with this option. It automatically 
implies --int-long-reent and --float-reent. 

--callee-saves function1[,function2][,function3].... 
The compiler by default uses a caller saves convention 
for register saving across function calls, however this 
can cause unnecessary register pushing & popping when 
calling small functions from larger functions. This 
option can be used to switch the register saving 
convention for the function names specified. The 
compiler will not save registers when calling these 
functions, no extra code will be generated at the entry 
& exit (function prologue & epilogue) for these 
functions to save & restore the registers used by these 
functions, this can SUBSTANTIALLY reduce code & improve 
run time performance of the generated code. In the 
future the compiler (with inter procedural analysis) 
will be able to determine the appropriate scheme to use 
for each function call. DO NOT use this option for 
built-in functions such as _mulint..., if this option 
is used for a library function the appropriate library 
function needs to be recompiled with the same option. 
If the project consists of multiple source files then 
all the source file should be compiled with the same -
-callee-saves option string. Also see #pragma callee_saves.

--debug When this option is used the compiler will 
generate debug information. The debug information 
collected in a file with .cdb extension can be used 
with the SDCDB. For more information see documentation 
for SDCDB. Another file with no extension contains 
debug information in AOMF or AOMF51 format which is 
commonly used by third party tools.

-S Stop after the stage of compilation proper; do not 
assemble. The output is an assembler code file for the 
input file specified.

--int-long-reent Integer (16 bit) and long (32 bit) 
libraries have been compiled as reentrant. Note by 
default these libraries are compiled as non-reentrant. 
See section Installation for more details.

--cyclomatic This option will cause the compiler to 
generate an information message for each function in 
the source file. The message contains some important 
information about the function. The number of edges and 
nodes the compiler detected in the control flow graph 
of the function, and most importantly the cyclomatic complexity
 see section on Cyclomatic Complexity for more details.

--float-reent Floating point library is compiled as reentrant
. See section Installation for more details.

--main-return This option can be used if the code 
generated is called by a monitor program or if the main 
routine includes an endless loop. This option might 
result in slightly smaller code and save two bytes of 
stack space. The return from the 'main' function will 
return to the function calling main. The default 
setting is to lock up i.e. generate a 'sjmp .'.

--nostdinc This will prevent the compiler from passing 
on the default include path to the preprocessor.

--nostdlib This will prevent the compiler from passing 
on the default library path to the linker.

--verbose Shows the various actions the compiler is performing.

-V Shows the actual commands the compiler is executing.

--no-c-code-in-asm Hides your ugly and inefficient 
c-code from the asm file, so you can always blame the 
compiler :)

--no-peep-comments Will not include peep-hole comments 
in the generated files.

--i-code-in-asm Include i-codes in the asm file. Sounds 
like noise but is most helpful for debugging the 
compiler itself.

--less-pedantic Disable some of the more pedantic warnings
 (jwk burps: please be more specific here, please!).

--disable-warning <nnnn> Disable specific warning with 
number <nnnn>.

--print-search-dirs Display the directories in the 
compiler's search path

--vc Display errors and warnings using MSVC style, so 
you can use SDCC with visual studio.

--use-stdout Send errors and warnings to stdout instead 
of stderr.

-Wa asmOption[,asmOption]... Pass the asmOption to the assembler
. See file sdcc/as/doc/asxhtm.html for assembler options.cd

--std-sdcc89 Generally follow the C89 standard, but 
allow SDCC features that conflict with the standard (default).

--std-c89 Follow the C89 standard and disable SDCC 
features that conflict with the standard.

--std-sdcc99 Generally follow the C99 standard, but 
allow SDCC features that conflict with the standard 
(incomplete support).

--std-c99 Follow the C99 standard and disable SDCC 
features that conflict with the standard (incomplete support).

--codeseg <Name> The name to be used for the code 
segment, default CSEG. This is useful if you need to 
tell the compiler to put the code in a special segment 
so you can later on tell the linker to put this segment 
in a special place in memory. Can be used for instance 
when using bank switching to put the code in a bank.

--constseg <Name> The name to be used for the const 
segment, default CONST. This is useful if you need to 
tell the compiler to put the const data in a special 
segment so you can later on tell the linker to put this 
segment in a special place in memory. Can be used for 
instance when using bank switching to put the const 
data in a bank.

more-pedantic Actually this is not a SDCC compiler 
option but if you want more warnings you can use a 
separate tool dedicated to syntax checking like splint<lyx:more-pedantic-SPLINT> [http://www.splint.org]
. To make your source files parseable by splint you 
will have to include lint.h in your source file and add 
brackets around extended keywords (like "__at (0xab)" and "
__interrupt (2)"). 
Splint has an excellent on line manual at [http://www.splint.org/manual/] and it's 
capabilities go beyond pure syntax checking. You'll 
need to tell splint the location of SDCC's include 
files so a typical command line could look like this: 
splint -I /usr/local/share/sdcc/include/mcs51/  myprogram.c

 Intermediate Dump Options<sub:Intermediate-Dump-Options>

The following options are provided for the purpose of 
retargetting and debugging the compiler. They provide a 
means to dump the intermediate code (iCode) generated 
by the compiler in human readable form at various 
stages of the compilation process. More on iCodes see 
chapter [sub:The-anatomy-of] "The anatomy of the compiler".

--dumpraw This option will cause the compiler to dump 
the intermediate code into a file of named <source 
filename>.dumpraw just after the intermediate code has 
been generated for a function, i.e. before any 
optimizations are done. The basic blocks at this stage 
ordered in the depth first number, so they may not be 
in sequence of execution.

--dumpgcse Will create a dump of iCode's, after global 
subexpression elimination, into a file named <source 
filename>.dumpgcse.

--dumpdeadcode Will create a dump of iCode's, after 
deadcode elimination, into a file named <source 
filename>.dumpdeadcode.

--dumploop Will create a dump of iCode's, after loop 
optimizations, into a file named <source filename>.dumploop.

--dumprange Will create a dump of iCode's, after live 
range analysis, into a file named <source filename>.dumprange.

--dumlrange Will dump the life ranges for all symbols.

--dumpregassign Will create a dump of iCode's, after 
register assignment, into a file named <source 
filename>.dumprassgn.

--dumplrange Will create a dump of the live ranges of iTemp's

--dumpall Will cause all the above mentioned dumps to 
be created.

 Redirecting output on Windows Shells

By default SDCC writes it's error messages to "standard error"
. To force all messages to "standard output" use --use-stdout
. Additionally, if you happen to have visual studio 
installed in your windows machine, you can use it to 
compile your sources using a custom build and the SDCC --vc
 option. Something like this should work:

c:\sdcc\bin\sdcc.exe --vc --model-large -c $(InputPath)

 Environment variables

SDCC recognizes the following environment variables:

SDCC_LEAVE_SIGNALS SDCC installs a signal handler to be 
able to delete temporary files after an user break (^C) 
or an exception. If this environment variable is set, 
SDCC won't install the signal handler in order to be 
able to debug SDCC.

TMP, TEMP, TMPDIR Path, where temporary files will be 
created. The order of the variables is the search 
order. In a standard *nix environment these variables 
are not set, and there's no need to set them. On 
Windows it's recommended to set one of them.

SDCC_HOME Path, see section [sub:Install-paths] " Install Paths".

SDCC_INCLUDE Path, see section [sub:Search-Paths] "Search Paths".

SDCC_LIB Path, see section [sub:Search-Paths] "Search Paths"..

There are some more environment variables recognized by 
SDCC, but these are solely used for debugging purposes. 
They can change or disappear very quickly, and will 
never be documented.

 Storage Class Language Extensions

 MCS51/DS390 Storage Class Language Extensions

In addition to the ANSI storage classes SDCC allows the 
following MCS51 specific storage classes:

 data / near

This is the default storage class for the Small Memory 
model (data and near can be used synonymously). 
Variables declared with this storage class will be 
allocated in the directly addressable portion of the 
internal RAM of a 8051, e.g.:

data unsigned char test_data;

Writing 0x01 to this variable generates the assembly code:

75*00 01   mov  _test_data,#0x01 

 xdata / far

Variables declared with this storage class will be 
placed in the external RAM. This is the default storage 
class for the Large Memory model, e.g.:

xdata unsigned char test_xdata;

Writing 0x01 to this variable generates the assembly code:

90s00r00   mov  dptr,#_test_xdata 
74 01      mov  a,#0x01 
F0         movx @dptr,a 

 idata

Variables declared with this storage class will be 
allocated into the indirectly addressable portion of 
the internal ram of a 8051, e.g.:

idata unsigned char test_idata;

Writing 0x01 to this variable generates the assembly code:

78r00       mov  r0,#_test_idata
76 01       mov  @r0,#0x01

Please note, the first 128 byte of idata physically 
access the same RAM as the data memory. The original 
8051 had 128 byte idata memory, nowadays most devices 
have 256 byte idata memory. The stack is located in 
idata memory.

 pdata

Paged xdata access is just as straightforward as using 
the other addressing modes of a 8051. It is typically 
located at the start of xdata and has a maximum size of 
256 bytes. The following example writes 0x01 to the 
pdata variable. Please note, pdata access physically 
accesses xdata memory. The high byte of the address is 
determined by port P2 (or in case of some 8051 variants 
by a separate Special Function Register, see section [sub:MCS51-variants]). 
This is the default storage class for the Medium Memory 
model, e.g.:

pdata unsigned char test_pdata;

Writing 0x01 to this variable generates the assembly code:

78r00      mov r0,#_test_pdata
74 01      mov a,#0x01 
F2         movx @r0,a

If the --xstack option is used the pdata memory area is 
followed by the xstack memory area and the sum of their 
sizes is limited to 256 bytes.

 code

'Variables' declared with this storage class will be 
placed in the code memory:

code unsigned char test_code;

Read access to this variable generates the assembly code:

90s00r6F   mov dptr,#_test_code
E4         clr a
93         movc a,@a+dptr 

char indexed arrays of characters in code memory can be 
accessed efficiently:

code char test_array[] = {'c','h','e','a','p'}; 

Read access to this array using an 8-bit unsigned index 
generates the assembly code:

E5*00      mov a,_index 

90s00r41   mov dptr,#_test_array

93         movc a,@a+dptr 

 bit

This is a data-type and a storage class specifier. When 
a variable is declared as a bit, it is allocated into 
the bit addressable memory of 8051, e.g.:

bit test_bit;

Writing 1 to this variable generates the assembly code:

D2*00       setb _test_bit

The bit addressable memory consists of 128 bits which 
are located from 0x20 to 0x2f in data memory. 
Apart from this 8051 specific storage class most 
architectures support ANSI-C bitfieldsNot really meant as examples, but nevertheless showing 
what bitfields are about: device/include/mc68hc908qy.h 
and support/regression/tests/bitfields.c
. In accordance with ISO/IEC 9899 bits and bitfields 
without an explicit signed modifier are implemented as unsigned.

 sfr / sfr16 / sfr32 / sbit

Like the bit keyword, sfr / sfr16 / sfr32 / sbit 
signify both a data-type and storage class, they are 
used to describe the special function registers and 
special bit variables of a 8051, eg:

sfr at 0x80 P0;  /* special function register P0 at 
location 0x80 */
/* 16 bit special function register combination for 
timer 0 */
/* with the high byte at location 0x8C and the low byte 
at location 0x8A */
sfr16 at 0x8C8A TMR0;
sbit at 0xd7 CY; /* CY (Carry Flag) */

Special function registers which are located on an 
address dividable by 8 are bit-addressable, an sbit 
addresses a specific bit within these sfr.
16 Bit and 32 bit special function register 
combinations which require a certain access order are 
better not declared using sfr16 or sfr32. Allthough 
SDCC usually accesses them Least Significant Byte (LSB) 
first, this is not guaranteed.

 Pointers to MCS51/DS390 specific memory spaces

SDCC allows (via language extensions) pointers to 
explicitly point to any of the memory spaces of the 
8051. In addition to the explicit pointers, the 
compiler uses (by default) generic pointers which can 
be used to point to any of the memory spaces.

Pointer declaration examples:

/* pointer physically in internal ram pointing to 
object in external ram */ 
xdata unsigned char * data p;

/* pointer physically in external ram pointing to 
object in internal ram */ 
data unsigned char * xdata p;

/* pointer physically in code rom pointing to data in 
xdata space */ 
xdata unsigned char * code p;

/* pointer physically in code space pointing to data in 
code space */ 
code unsigned char * code p;

/* the following is a generic pointer physically 
located in xdata space */
char * xdata p;

/* the following is a function pointer physically 
located in data space */
char (* data fp)(void);

Well you get the idea. 

All unqualified pointers are treated as 3-byte (4-byte 
for the ds390) generic pointers. 

The highest order byte of the generic pointers contains 
the data space information. Assembler support routines 
are called whenever data is stored or retrieved using 
generic pointers. These are useful for developing 
reusable library routines. Explicitly specifying the 
pointer type will generate the most efficient code.

 Notes on MCS51 memory layout

The 8051 family of microcontrollers have a minimum of 
128 bytes of internal RAM memory which is structured as follows:

- Bytes 00-1F - 32 bytes to hold up to 4 banks of the 
registers R0 to R7, 
- Bytes 20-2F - 16 bytes to hold 128 bit variables and, 
- Bytes 30-7F - 80 bytes for general purpose use.


Additionally some members of the MCS51 family may have 
up to 128 bytes of additional, indirectly addressable, 
internal RAM memory (idata). Furthermore, some chips 
may have some built in external memory (xdata) which 
should not be confused with the internal, directly 
addressable RAM memory (data). Sometimes this built in 
xdata memory has to be activated before using it (you 
can probably find this information on the datasheet of 
the microcontroller your are using, see also section [sub:Startup-Code] 
Startup-Code).

Normally SDCC will only use the first bank of registers 
(register bank 0), but it is possible to specify that 
other banks of registers (keyword using ) should be 
used in interrupt routines. By default, the compiler 
will place the stack after the last byte of allocated 
memory for variables. For example, if the first 2 banks 
of registers are used, and only four bytes are used for 
data variables, it will position the base of the 
internal stack at address 20 (0x14). This implies that 
as the stack grows, it will use up the remaining 
register banks, and the 16 bytes used by the 128 bit 
variables, and 80 bytes for general purpose use. If any 
bit variables are used, the data variables will be 
placed in unused register banks and after the byte 
holding the last bit variable. For example, if register 
banks 0 and 1 are used, and there are 9 bit variables 
(two bytes used), data variables will be placed 
starting from address 0x10 to 0x20 and continue at 
address 0x22. You can also use --data-loc to specify 
the start address of the data and --iram-size to 
specify the size of the total internal RAM 
(data+idata). 

By default the 8051 linker will place the stack after 
the last byte of (i)data variables. Option --stack-loc 
allows you to specify the start of the stack, i.e. you 
could start it after any data in the general purpose 
area. If your microcontroller has additional indirectly 
addressable internal RAM (idata) you can place the 
stack on it. You may also need to use --xdata-loc to 
set the start address of the external RAM (xdata) and --xram-size
 to specify its size. Same goes for the code memory, 
using --code-loc and --code-size. If in doubt, don't 
specify any options and see if the resulting memory 
layout is appropriate, then you can adjust it.

The linker generates two files with memory allocation 
information. The first, with extension .map shows all 
the variables and segments. The second with extension .mem
 shows the final memory layout. The linker will 
complain either if memory segments overlap, there is 
not enough memory, or there is not enough space for 
stack. If you get any linking warnings and/or errors 
related to stack or segments allocation, take a look at 
either the .map or .mem files to find out what the 
problem is. The .mem file may even suggest a solution 
to the problem.

 Z80/Z180 Storage Class Language Extensions

 sfr (in/out to 8-bit addresses)

The Z80 family has separate address spaces for memory 
and input/output memory. I/O memory is accessed with 
special instructions, e.g.:

sfr at 0x78 IoPort;  /* define a var in I/O space at 78h 
called IoPort */ 

Writing 0x01 to this variable generates the assembly code:

3E 01      ld a,#0x01
D3 78      out (_IoPort),a 

 banked sfr (in/out to 16-bit addresses)

The keyword banked is used to support 16 bit addresses 
in I/O memory e.g.:

sfr banked at 0x123 IoPort; 

Writing 0x01 to this variable generates the assembly code:

01 23 01   ld bc,#_IoPort
3E 01      ld a,#0x01 
ED 79      out (c),a 

 sfr (in0/out0 to 8 bit addresses on Z180/HD64180)

The compiler option --portmode=180 (80) and a compiler #pragma 
portmode=z180 (z80) is used to turn on (off) the 
Z180/HD64180 port addressing instructions in0/out0 
instead of in/out. If you include the file z180.h this 
will be set automatically.

 HC08 Storage Class Language Extensions

 data 

The data storage class declares a variable that resides 
in the first 256 bytes of memory (the direct page). The 
HC08 is most efficient at accessing variables 
(especially pointers) stored here.

 xdata 

The xdata storage class declares a variable that can 
reside anywhere in memory. This is the default if no 
storage class is specified. 

 Absolute Addressing

Data items can be assigned an absolute address with the at
 <address> keyword, in addition to a storage class, e.g.:

xdata at 0x7ffe unsigned int chksum;

In the above example the variable chksum will be 
located at 0x7ffe and 0x7fff of the external ram. The 
compiler does not reserve any space for variables 
declared in this way (they are implemented with an 
equate in the assembler). Thus it is left to the 
programmer to make sure there are no overlaps with 
other variables that are declared without the absolute 
address. The assembler listing file (.lst) and the 
linker output files (.rst) and (.map) are good places 
to look for such overlaps. Variables with an absolute 
address are not initialized.

In case of memory mapped I/O devices the keyword 
volatile has to be used to tell the compiler that 
accesses might not be removed:

volatile xdata at 0x8000 unsigned char PORTA_8255;

For some architectures (mcs51) array accesses are more 
efficient if an (xdata/far) array starts at a block 
(256 byte) boundary (section [sub:A-Step-by Assembler Introduction] has an example).
Absolute addresses can be specified for variables in 
all storage classes, e.g.:

bit at 0x02 bvar;

The above example will allocate the variable at offset 
0x02 in the bit-addressable space. There is no real 
advantage to assigning absolute addresses to variables 
in this manner, unless you want strict control over all 
the variables allocated. One possible use would be to 
write hardware portable code. For example, if you have 
a routine that uses one or more of the microcontroller 
I/O pins, and such pins are different for two different 
hardwares, you can declare the I/O pins in your routine using:

extern volatile bit MOSI;    /* master out, slave in */
extern volatile bit MISO;    /* master in, slave out */
extern volatile bit MCLK;    /* master clock */

/* Input and Output of a byte on a 3-wire serial bus.
   If needed adapt polarity of clock, polarity of data and 
bit order
 */
unsigned char spi_io(unsigned char out_byte) 
{ 
    unsigned char i=8;
    do { 
        MOSI = out_byte & 0x80; 
        out_byte <<= 1;
        MCLK = 1; 
        /* _asm nop _endasm; */        /* for slow peripherals */
        if(MISO) 
            out_byte += 1; 
        MCLK = 0; 
    } while(--i);
    return out_byte; 
}

Then, someplace in the code for the first hardware you 
would use

bit at 0x80 MOSI;    /* I/O port 0, bit 0 */
bit at 0x81 MISO;    /* I/O port 0, bit 1 */
bit at 0x82 MCLK;    /* I/O port 0, bit 2 */

Similarly, for the second hardware you would use

bit at 0x83 MOSI;    /* I/O port 0, bit 3 */
bit at 0x91 MISO;    /* I/O port 1, bit 1 */
bit at 0x92 MCLK;    /* I/O port 1, bit 2 */

and you can use the same hardware dependent routine 
without changes, as for example in a library. This is 
somehow similar to sbit, but only one absolute address 
has to be specified in the whole project.

 Parameters & Local Variables<sec:Parameters-and-Local-Variables>

Automatic (local) variables and parameters to functions 
can either be placed on the stack or in data-space. The 
default action of the compiler is to place these 
variables in the internal RAM (for small model) or 
external RAM (for large model). This in fact makes them 
similar to static so by default functions are non-reentrant
. 

They can be placed on the stack by using the --stack-auto
 option, by using #pragma stackauto or by using the reentrant
 keyword in the function declaration, e.g.:

unsigned char foo(char i) reentrant 
{ 
    ... 
}

Since stack space on 8051 is limited, the reentrant 
keyword or the --stack-auto option should be used 
sparingly. Note that the reentrant keyword just means 
that the parameters & local variables will be allocated 
to the stack, it does not mean that the function is 
register bank independent.

Local variables can be assigned storage classes and absolute
 addresses, e.g.: 

unsigned char foo() 
{
    xdata unsigned char i;
    bit bvar;
    data at 0x31 unsigned char j;
    ... 
}

In the above example the variable i will be allocated 
in the external ram, bvar in bit addressable space and 
j in internal ram. When compiled with --stack-auto or 
when a function is declared as reentrant this should 
only be done for static variables.

Parameters however are not allowed any storage class, 
(storage classes for parameters will be ignored), their 
allocation is governed by the memory model in use, and 
the reentrancy options.

It is however allowed to use bit parameters in 
reentrant functions and also non-static local bit 
variables are supported. Efficient use is limited to 8 
semi-bitregisters in bit space. They are pushed and 
popped to stack as a single byte just like the normal registers.

 Overlaying<sub:Overlaying>

For non-reentrant functions SDCC will try to reduce 
internal ram space usage by overlaying parameters and 
local variables of a function (if possible). Parameters 
and local variables of a function will be allocated to 
an overlayable segment if the function has no other 
function calls and the function is non-reentrant and 
the memory model is small. If an explicit storage class 
is specified for a local variable, it will NOT be overlayed.

Note that the compiler (not the linkage editor) makes 
the decision for overlaying the data items. Functions 
that are called from an interrupt service routine 
should be preceded by a #pragma nooverlay if they are 
not reentrant.

Also note that the compiler does not do any processing 
of inline assembler code, so the compiler might 
incorrectly assign local variables and parameters of a 
function into the overlay segment if the inline 
assembler code calls other c-functions that might use 
the overlay. In that case the #pragma nooverlay should 
be used.

Parameters and local variables of functions that 
contain 16 or 32 bit multiplication or division will 
NOT be overlayed since these are implemented using 
external functions, e.g.:

#pragma save 
#pragma nooverlay 
void set_error(unsigned char errcd) 
{
    P3 = errcd;
} 
#pragma restore 

void some_isr () interrupt 2
{
    ...
    set_error(10);
    ... 
}

In the above example the parameter errcd for the 
function set_error would be assigned to the overlayable 
segment if the #pragma nooverlay was not present, this 
could cause unpredictable runtime behavior when called 
from an interrupt service routine. The #pragma nooverlay 
ensures that the parameters and local variables for the 
function are NOT overlayed.

 Interrupt Service Routines<sub:Interrupt-Service-Routines>

 General Information

SDCC allows interrupt service routines to be coded in 
C, with some extended keywords.

void timer_isr (void) interrupt 1 using 1 
{ 
    ... 
}

The optional number following the interrupt keyword is 
the interrupt number this routine will service. When 
present, the compiler will insert a call to this 
routine in the interrupt vector table for the interrupt 
number specified. If you have multiple source files in 
your project, interrupt service routines can be present 
in any of them, but a prototype of the isr MUST be 
present or included in the file that contains the 
function main. The optional using keyword can be used 
to tell the compiler to use the specified register bank 
(8051 specific) when generating code for this function. 


Interrupt service routines open the door for some very 
interesting bugs:
If an interrupt service routine changes variables which 
are accessed by other functions these variables have to 
be declared volatile. 

If the access to these variables is not atomic (i.e. 
the processor needs more than one instruction for the 
access and could be interrupted while accessing the 
variable) the interrupt must be disabled during the 
access to avoid inconsistent data. Access to 16 or 32 
bit variables is obviously not atomic on 8 bit CPUs and 
should be protected by disabling interrupts. You're not 
automatically on the safe side if you use 8 bit 
variables though. We need an example here: f.e. on the 
8051 the harmless looking "flags |= 0x80;" is not atomic if 
flags resides in xdata. Setting "flags |= 0x40;" from 
within an interrupt routine might get lost if the 
interrupt occurs at the wrong time. "counter += 8;" is not 
atomic on the 8051 even if counter is located in data 
memory. Bugs like these are hard to reproduce and can 
cause a lot of trouble. 

The return address and the registers used in the 
interrupt service routine are saved on the stack so 
there must be sufficient stack space. If there isn't 
variables or registers (or even the return address 
itself) will be corrupted. This stack overflow is most 
likely to happen if the interrupt occurs during the "deepest"
 subroutine when the stack is already in use for f.e. 
many return addresses.

A special note here, int (16 bit) and long (32 bit) 
integer division, multiplication & modulus and floating-point
 operations are implemented using external support 
routines developed in ANSI-C. If an interrupt service 
routine needs to do any of these operations then the 
support routines (as mentioned in a following section) 
will have to be recompiled using the --stack-auto 
option and the source file will need to be compiled 
using the --int-long-reent compiler option.

Calling other functions from an interrupt service 
routine is not recommended, avoid it if possible. Note 
that when some function is called from an interrupt 
service routine it should be preceded by a #pragma nooverlay
 if it is not reentrant. Furthermore nonreentrant 
functions should not be called from the main program 
while the interrupt service routine might be active. 
They also must not be called from low priority 
interrupt service routines while a high priority 
interrupt service routine might be active. You could 
use semaphores or make the function critical if all 
parameters are passed in registers.

Also see section [sub:Overlaying] about Overlaying and section [sub:Functions-using-private-banks] about 
Functions using private register banks.

 MCS51/DS390 Interrupt Service Routines

Interrupt numbers and the corresponding address & 
descriptions for the Standard 8051/8052 are listed 
below. SDCC will automatically adjust the interrupt 
vector table to the maximum interrupt number specified.


+--------------+-----------------+----------------+
| Interrupt #  |  Description    | Vector Address |
+--------------+-----------------+----------------+
+--------------+-----------------+----------------+
|      0       |   External 0    |     0x0003     |
+--------------+-----------------+----------------+
|      1       |    Timer 0      |     0x000B     |
+--------------+-----------------+----------------+
|      2       |   External 1    |     0x0013     |
+--------------+-----------------+----------------+
|      3       |    Timer 1      |     0x001B     |
+--------------+-----------------+----------------+
|      4       |     Serial      |     0x0023     |
+--------------+-----------------+----------------+
|      5       | Timer 2 (8052)  |     0x002B     |
+--------------+-----------------+----------------+



If the interrupt service routine is defined without using
 a register bank or with register bank 0 (using 0), the 
compiler will save the registers used by itself on the 
stack upon entry and restore them at exit, however if 
such an interrupt service routine calls another 
function then the entire register bank will be saved on 
the stack. This scheme may be advantageous for small 
interrupt service routines which have low register usage.

If the interrupt service routine is defined to be using 
a specific register bank then only a, b, dptr & psw are 
saved and restored, if such an interrupt service 
routine calls another function (using another register 
bank) then the entire register bank of the called 
function will be saved on the stack. This scheme is 
recommended for larger interrupt service routines.

 HC08 Interrupt Service Routines

Since the number of interrupts available is chip 
specific and the interrupt vector table always ends at 
the last byte of memory, the interrupt numbers 
corresponds to the interrupt vectors in reverse order 
of address. For example, interrupt 1 will use the 
interrupt vector at 0xfffc, interrupt 2 will use the 
interrupt vector at 0xfffa, and so on. However, 
interrupt 0 (the reset vector at 0xfffe) is not 
redefinable in this way; instead see section [sub:Startup-Code] for 
details on customizing startup.

 Z80 Interrupt Service Routines

The Z80 uses several different methods for determining 
the correct interrupt vector depending on the hardware 
implementation. Therefore, SDCC ignores the optional 
interrupt number and does not attempt to generate an 
interrupt vector table.

By default, SDCC generates code for a maskable 
interrupt, which uses a RETI instruction to return from 
the interrupt. To write an interrupt handler for the 
non-maskable interrupt, which needs a RETN instruction 
instead, add the critical keyword:

void nmi_isr (void) critical interrupt
{ 
    ... 
}

However if you need to create a non-interruptable 
interrupt service routine you would also require the 
critical keyword. To distinguish between this and an 
nmi_isr you must provide an interrupt number.

 Enabling and Disabling Interrupts

 Critical Functions and Critical Statements

A special keyword may be associated with a block or a 
function declaring it as critical. SDCC will generate 
code to disable all interrupts upon entry to a critical 
function and restore the interrupt enable to the 
previous state before returning. Nesting critical 
functions will need one additional byte on the stack 
for each call.

int foo () critical 
{ 
    ... 
    ... 
}

The critical attribute maybe used with other attributes 
like reentrant.
The keyword critical may also be used to disable 
interrupts more locally:

critical{ i++; }

More than one statement could have been included in the block.

 Enabling and Disabling Interrupts directly

Interrupts can also be disabled and enabled directly (8051):

EA = 0;            or:           EA_SAVE = EA;

...                              EA = 0;

EA = 1;                          ...

                                 EA = EA_SAVE;

On other architectures which have seperate opcodes for 
enabling and disabling interrupts you might want to 
make use of defines with inline assembly (HC08):

#define CLI _asm  cli  _endasm; 

#define SEI _asm  sei  _endasm; 

...

Note: it is sometimes sufficient to disable only a 
specific interrupt source like f.e. a timer or serial 
interrupt by manipulating an interrupt mask register. 

Usually the time during which interrupts are disabled 
should be kept as short as possible. This minimizes 
both interrupt latency (the time between the occurrence 
of the interrupt and the execution of the first code in 
the interrupt routine) and interrupt jitter (the 
difference between the shortest and the longest 
interrupt latency). These really are something 
different, f.e. a serial interrupt has to be served 
before its buffer overruns so it cares for the maximum 
interrupt latency, whereas it does not care about 
jitter. On a loudspeaker driven via a digital to analog 
converter which is fed by an interrupt a latency of a 
few milliseconds might be tolerable, whereas a much 
smaller jitter will be very audible.

You can reenable interrupts within an interrupt routine 
and on some architectures you can make use of two (or 
more) levels of interrupt priorities. On some 
architectures which don't support interrupt priorities 
these can be implemented by manipulating the interrupt 
mask and reenabling interrupts within the interrupt 
routine. Check there is sufficient space on the stack 
and don't add complexity unless you have to. 

 Semaphore locking (mcs51/ds390)

Some architectures (mcs51/ds390) have an atomic bit 
test and clear instruction. These type of instructions 
are typically used in preemptive multitasking systems, 
where a routine f.e. claims the use of a data structure 
('acquires a lock on it'), makes some modifications and 
then releases the lock when the data structure is 
consistent again. The instruction may also be used if 
interrupt and non-interrupt code have to compete for a 
resource. With the atomic bit test and clear 
instruction interrupts don't have to be disabled for 
the locking operation. 

SDCC generates this instruction if the source follows 
this pattern:

volatile bit resource_is_free; 

if (resource_is_free) 
  { 
    resource_is_free=0; 
    ... 
    resource_is_free=1;
  } 

Note, mcs51 and ds390 support only an atomic bit test 
and clear instruction (as opposed to atomic bit test 
and set).

 Functions using private register banks<sub:Functions-using-private-banks> (mcs51/ds390)

Some architectures have support for quickly changing 
register sets. SDCC supports this feature with the using
 attribute (which tells the compiler to use a register bank
 other than the default bank zero). It should only be 
applied to interrupt functions (see footnote below). 
This will in most circumstances make the generated ISR 
code more efficient since it will not have to save 
registers on the stack.

The using attribute will have no effect on the 
generated code for a non-interrupt function (but may 
occasionally be useful anywaypossible exception: if a function is called ONLY from 
'interrupt' functions using a particular bank, it can 
be declared with the same 'using' attribute as the 
calling 'interrupt' functions. For instance, if you 
have several ISRs using bank one, and all of them call 
memcpy(), it might make sense to create a specialized 
version of memcpy() 'using 1', since this would prevent 
the ISR from having to save bank zero to the stack on 
entry and switch to bank zero before calling the function
).
(pending: I don't think this has been done yet)

An interrupt function using a non-zero bank will assume 
that it can trash that register bank, and will not save 
it. Since high-priority interrupts can interrupt 
low-priority ones on the 8051 and friends, this means 
that if a high-priority ISR using a particular bank 
occurs while processing a low-priority ISR using the 
same bank, terrible and bad things can happen. To 
prevent this, no single register bank should be used by 
both a high priority and a low priority ISR. This is 
probably most easily done by having all high priority 
ISRs use one bank and all low priority ISRs use 
another. If you have an ISR which can change priority 
at runtime, you're on your own: I suggest using the 
default bank zero and taking the small performance hit.

It is most efficient if your ISR calls no other 
functions. If your ISR must call other functions, it is 
most efficient if those functions use the same bank as 
the ISR (see note 1 below); the next best is if the 
called functions use bank zero. It is very inefficient 
to call a function using a different, non-zero bank 
from an ISR. 

 Startup Code<sub:Startup-Code>

 MCS51/DS390 Startup Code

The compiler inserts a call to the C routine 
_sdcc_external_startup() at the start of the CODE area. 
This routine is in the runtime library. By default this 
routine returns 0, if this routine returns a non-zero 
value, the static & global variable initialization will 
be skipped and the function main will be invoked. 
Otherwise static & global variables will be initialized 
before the function main is invoked. You could add a 
_sdcc_external_startup() routine to your program to 
override the default if you need to setup hardware or 
perform some other critical operation prior to static & 
global variable initialization. On some mcs51 variants xdata
 memory has to be explicitly enabled before it can be 
accessed or if the watchdog needs to be disabled, this 
is the place to do it. The startup code clears all 
internal data memory, 256 bytes by default, but from 0 
to n-1 if --iram-sizen is used. (recommended for 
Chipcon CC1010).

See also the compiler option --no-xinit-opt and section [sub:MCS51-variants] 
about MCS51-variants.

 HC08 Startup Code

The HC08 startup code follows the same scheme as the 
MCS51 startup code.

 Z80 Startup Code

On the Z80 the startup code is inserted by linking with 
crt0.o which is generated from 
sdcc/device/lib/z80/crt0.s. If you need a different 
startup code you can use the compiler option --no-std-crt0
 and provide your own crt0.o. 

 Inline Assembler Code

 A Step by Step Introduction<sub:A-Step-by Assembler Introduction>

Starting from a small snippet of c-code this example 
shows for the MCS51 how to use inline assembly, access 
variables, a function parameter and an array in xdata 
memory. The example uses an MCS51 here but is easily 
adapted for other architectures. This is a buffer 
routine which should be optimized:

unsigned char far at 0x7f00 buf[0x100];
unsigned char head,tail;

void to_buffer( unsigned char c ) 
{
    if( head != tail-1 ) 
        buf[ head++ ] = c;    /* access to a 256 byte aligned array */
} 

If the code snippet (assume it is saved in buffer.c) is 
compiled with SDCC then a corresponding buffer.asm file 
is generated. We define a new function to_buffer_asm() 
in file buffer.c in which we cut and paste the 
generated code, removing unwanted comments and some 
':'. Then add "_asm" and "_endasm;" to the beginning and 
the end of the function body:

/* With a cut and paste from the .asm file, we have 
something to start with.
   The function is not yet OK! (registers aren't saved) */ 
void to_buffer_asm( unsigned char c ) 
{ 
    _asm
    mov  r2,dpl 
;buffer.c if( head != tail-1 ) 
    mov  a,_tail 
    dec  a 
    mov  r3,a 
    mov  a,_head 
    cjne a,ar3,00106$ 
    ret
00106$: 
;buffer.c buf[ head++ ] = c; /* access to a 256 byte 
aligned array */
    mov  r3,_head 
    inc  _head 
    mov  dpl,r3 
    mov  dph,#(_buf >> 8) 
    mov  a,r2 
    movx @dptr,a 
00103$: 
    ret
    _endasm;
} 

The new file buffer.c should compile with only one 
warning about the unreferenced function argument 'c'. 
Now we hand-optimize the assembly code and insert an 
#define USE_ASSEMBLY (1) and finally have:

unsigned char far at 0x7f00 buf[0x100];
unsigned char head,tail;
#define USE_ASSEMBLY (1)

#if !USE_ASSEMBLY

void to_buffer( unsigned char c )
{
    if( head != tail-1 )
        buf[ head++ ] = c;
}

#else

void to_buffer( unsigned char c )
{
    c; // to avoid warning: unreferenced function argument
    _asm
        ; save used registers here. 
        ; If we were still using r2,r3 we would have to push 
them here. 
; if( head != tail-1 )
        mov  a,_tail
        dec  a
        xrl  a,_head
        ; we could do an ANL a,#0x0f here to use a smaller 
buffer (see below)
        jz   t_b_end$
        ;
; buf[ head++ ] = c;
        mov  a,dpl        ; dpl holds lower byte of function argument
        mov  dpl,_head    ; buf is 0x100 byte aligned so head can 
be used directly
        mov  dph,#(_buf>>8)
        movx @dptr,a
        inc  _head
        ; we could do an ANL _head,#0x0f here to use a smaller 
buffer (see above)
t_b_end$:
        ; restore used registers here 
    _endasm;
}
#endif

The inline assembler code can contain any valid code 
understood by the assembler, this includes any 
assembler directives and comment linesThe assembler does not like some characters like ':' or 
''' in comments. You'll find an 100+ pages assembler 
manual in sdcc/as/doc/asxhtm.html
. The compiler does not do any validation of the code 
within the _asm ... _endasm; keyword pair. Specifically 
it will not know which registers are used and thus 
register pushing/popping has to be done manually. 

It is recommended that each assembly instruction 
(including labels) be placed in a separate line (as the 
example shows). When the --peep-asm command line option 
is used, the inline assembler code will be passed 
through the peephole optimizer. There are only a few 
(if any) cases where this option makes sense, it might 
cause some unexpected changes in the inline assembler 
code. Please go through the peephole optimizer rules 
defined in file SDCCpeeph.def before using this option.

 Naked Functions<sub:Naked-Functions>

A special keyword may be associated with a function 
declaring it as _naked. The _naked function modifier 
attribute prevents the compiler from generating prologue
 and epilogue code for that function. This means that 
the user is entirely responsible for such things as 
saving any registers that may need to be preserved, 
selecting the proper register bank, generating the 
return instruction at the end, etc. Practically, this 
means that the contents of the function must be written 
in inline assembler. This is particularly useful for 
interrupt functions, which can have a large (and often 
unnecessary) prologue/epilogue. For example, compare 
the code generated by these two functions:

volatile data unsigned char counter;

void simpleInterrupt(void) interrupt 1
{
    counter++;
}

void nakedInterrupt(void) interrupt 2 _naked
{
    _asm
      inc     _counter ; does not change flags, no need to save psw
      reti    ; MUST explicitly include ret or reti in _naked function.
    _endasm;
}

For an 8051 target, the generated simpleInterrupt looks like:

_simpleInterrupt:
    push    acc
    push    b
    push    dpl
    push    dph
    push    psw
    mov     psw,#0x00
    inc     _counter
    pop     psw
    pop     dph
    pop     dpl
    pop     b
    pop     acc
    reti

whereas nakedInterrupt looks like:

_nakedInterrupt:
    inc    _counter ; does not change flags, no need to save psw
    reti            ; MUST explicitly include ret or reti in _naked function

The related directive #pragma exclude allows a more 
fine grained control over pushing & popping the registers.

While there is nothing preventing you from writing C 
code inside a _naked function, there are many ways to 
shoot yourself in the foot doing this, and it is 
recommended that you stick to inline assembler.

 Use of Labels within Inline Assembler

SDCC allows the use of in-line assembler with a few 
restrictions regarding labels. In older versions of the 
compiler all labels defined within inline assembler 
code had to be of the form nnnnn$ where nnnn is a 
number less than 100 (which implies a limit of utmost 
100 inline assembler labels per function). 

_asm 
    mov     b,#10 
00001$: 
    djnz    b,00001$ 
_endasm ;

Inline assembler code cannot reference any C-Labels, 
however it can reference labels defined by the inline 
assembler, e.g.:

foo() { 
    /* some c code */ 
    _asm 
      ; some assembler code 
      ljmp $0003 
    _endasm; 
    /* some more c code */ 
clabel:  /* inline assembler cannot reference this label 
*/ 
    _asm
    $0003: ;label (can be referenced by inline assembler 
only) 
    _endasm ; 
    /* some more c code */
}

In other words inline assembly code can access labels 
defined in inline assembly within the scope of the 
function. The same goes the other way, i.e. labels 
defines in inline assembly can not be accessed by C statements.

 Interfacing with Assembler Code

 Global Registers used for Parameter Passing

The compiler always uses the global registers DPL, DPH, B
 and ACC to pass the first parameter to a routine. The 
second parameter onwards is either allocated on the 
stack (for reentrant routines or if --stack-auto is 
used) or in data / xdata memory (depending on the 
memory model). 

 Assembler Routine (non-reentrant)

In the following example the function c_func calls an 
assembler routine asm_func, which takes two parameters.

extern int asm_func(unsigned char, unsigned char);

int c_func (unsigned char i, unsigned char j)
{
    return asm_func(i,j);
}

int main()
{
    return c_func(10,9);
}

The corresponding assembler function is:

.globl _asm_func_PARM_2 
        .globl _asm_func 
        .area OSEG 
_asm_func_PARM_2:
        .ds    1 
        .area CSEG 
_asm_func: 
        mov    a,dpl 
        add    a,_asm_func_PARM_2 
        mov    dpl,a 
        mov    dph,#0x00 
        ret

Note here that the return values are placed in 'dpl' - 
One byte return value, 'dpl' LSB & 'dph' MSB for two 
byte values. 'dpl', 'dph' and 'b' for three byte values 
(generic pointers) and 'dpl','dph','b' & 'acc' for four 
byte values.

The parameter naming convention is 
_<function_name>_PARM_<n>, where n is the parameter 
number starting from 1, and counting from the left. The 
first parameter is passed in "dpl" for a one byte 
parameter, "dptr" for two bytes, "b,dptr" for three bytes 
and "acc,b,dptr" for a four bytes parameter. The variable 
name for the second parameter will be _<function_name>_PARM_2.

Assemble the assembler routine with the following command:

asx8051 -losg asmfunc.asm

Then compile and link the assembler routine to the C 
source file with the following command:

sdcc cfunc.c asmfunc.rel

 Assembler Routine (reentrant)

In this case the second parameter onwards will be 
passed on the stack, the parameters are pushed from 
right to left i.e. after the call the leftmost 
parameter will be on the top of the stack. Here is an example:

extern int asm_func(unsigned char, unsigned char);

int c_func (unsigned char i, unsigned char j) reentrant 
{ 
    return asm_func(i,j); 
} 

int main() 
{ 
    return c_func(10,9); 
}

The corresponding assembler routine is:

.globl _asm_func 
_asm_func: 
    push  _bp 
    mov _bp,sp 
    mov r2,dpl
    mov a,_bp 
    add a,#0xfd 
    mov r0,a 
    add  a,#0xfc ;?
    mov  r1,a 
    mov  a,@r0 
    add  a,r2 ;?
    mov  dpl,a 
    mov  dph,#0x00 
    mov  sp,_bp 
    pop  _bp 
    ret

The compiling and linking procedure remains the same, 
however note the extra entry & exit linkage required 
for the assembler code, _bp is the stack frame pointer 
and is used to compute the offset into the stack for 
parameters and local variables.

 int (16 bit) and long (32 bit) Support

For signed & unsigned int (16 bit) and long (32 bit) 
variables, division, multiplication and modulus 
operations are implemented by support routines. These 
support routines are all developed in ANSI-C to 
facilitate porting to other MCUs, although some model 
specific assembler optimizations are used. The 
following files contain the described routines, all of 
them can be found in <installdir>/share/sdcc/lib.


+---------------+------------------------------------------+
|   Function    |               Description                |
+---------------+------------------------------------------+
+---------------+------------------------------------------+
|  _mulint.c    |          16 bit multiplication           |
+---------------+------------------------------------------+
| _divsint.c    |  signed 16 bit division (calls _divuint) |
+---------------+------------------------------------------+
| _divuint.c    |         unsigned 16 bit division         |
+---------------+------------------------------------------+
|  _modsint.c   |  signed 16 bit modulus (calls _moduint)  |
+---------------+------------------------------------------+
|  _moduint.c   |         unsigned 16 bit modulus          |
+---------------+------------------------------------------+
|  _mullong.c   |          32 bit multiplication           |
+---------------+------------------------------------------+
| _divslong.c   |   signed 32 division (calls _divulong)   |
+---------------+------------------------------------------+
| _divulong.c   |           unsigned 32 division           |
+---------------+------------------------------------------+
| _modslong.c   |  signed 32 bit modulus (calls _modulong) |
+---------------+------------------------------------------+
| _modulong.c   |         unsigned 32 bit modulus          |
+---------------+------------------------------------------+



Since they are compiled as non-reentrant, interrupt 
service routines should not do any of the above 
operations. If this is unavoidable then the above 
routines will need to be compiled with the --stack-auto 
option, after which the source program will have to be 
compiled with --int-long-reent option. Notice that you 
don't have to call these routines directly. The 
compiler will use them automatically every time an 
integer operation is required.

 Floating Point Support

SDCC supports IEEE (single precision 4 bytes) floating 
point numbers.The floating point support routines are 
derived from gcc's floatlib.c and consist of the 
following routines:


+--------------+------------------------------------------------+
|  Function    |                  Description                   |
+--------------+------------------------------------------------+
+--------------+------------------------------------------------+
|  _fsadd.c    |           add floating point numbers           |
+--------------+------------------------------------------------+
|  _fssub.c    |        subtract floating point numbers         |
+--------------+------------------------------------------------+
|  _fsdiv.c    |         divide floating point numbers          |
+--------------+------------------------------------------------+
|  _fsmul.c    |        multiply floating point numbers         |
+--------------+------------------------------------------------+
| _fs2uchar.c  |    convert floating point to unsigned char     |
+--------------+------------------------------------------------+
| _fs2char.c   |     convert floating point to signed char      |
+--------------+------------------------------------------------+
| _fs2uint.c   |     convert floating point to unsigned int     |
+--------------+------------------------------------------------+
|  _fs2int.c   |      convert floating point to signed int      |
+--------------+------------------------------------------------+
| _fs2ulong.c  |    convert floating point to unsigned long     |
+--------------+------------------------------------------------+
| _fs2long.c   |     convert floating point to signed long      |
+--------------+------------------------------------------------+
| _uchar2fs.c  |    convert unsigned char to floating point     |
+--------------+------------------------------------------------+
| _char2fs.c   |     convert char to floating point number      |
+--------------+------------------------------------------------+
| _uint2fs.c   |     convert unsigned int to floating point     |
+--------------+------------------------------------------------+
|  _int2fs.c   |     convert int to floating point numbers      |
+--------------+------------------------------------------------+
| _ulong2fs.c  | convert unsigned long to floating point number |
+--------------+------------------------------------------------+
| _long2fs.c   |     convert long to floating point number      |
+--------------+------------------------------------------------+



These support routines are developed in ANSI-C so there 
is room for space and speed improvementThe floating point routines for the mcs51 are 
implemented in assembler
. Note if all these routines are used simultaneously 
the data space might overflow. For serious floating 
point usage the large model might be needed. Also 
notice that you don't have to call this routines 
directly. The compiler will use them automatically 
every time a floating point operation is required.

 Library Routines

<pending: this is messy and incomplete - a little more 
information is in sdcc/doc/libdoc.txt >

 Compiler support routines (_gptrget, _mulint etc.)

 Stdclib functions (puts, printf, strcat etc.)

 <stdio.h>

As usual on embedded systems you have to provide your 
own getchar() and putchar() routines. SDCC does not 
know whether the system connects to a serial line with 
or without handshake, LCD, keyboard or other device. 
You'll find examples for serial routines f.e. in sdcc/device/lib.

The default printf()implementation in printf_large.c 
does not support float (except on ds390). To enable 
this recompile it with the option -DUSE_FLOATS=1 on the 
command line. Use--model-large for the mcs51 port, 
since this uses a lot of memory.

If you're short on memory you might want to use printf_small()
 instead of printf(). For the mcs51 there additionally 
are assembly versions printf_tiny() and printf_fast() 
and printf_fast_f() which should fit the requirements 
of many embedded systems (printf_fast() can be 
customized by unsetting #defines to not support long 
variables and field widths).

 Math functions (sin, pow, sqrt etc.)

 Other libraries

Libraries included in SDCC should have a license at 
least as liberal as the GNU Lesser General Public License
 LGPL.

license statements for the libraries are missing. 
sdcc/device/lib/ser_ir.c

or _decdptr f.e. come with a GPL (as opposed to LGPL) 
License - this will not be liberal enough for many 
embedded programmers.

If you have ported some library or want to share 
experience about some code which f.e. falls into any of 
these categories Busses (I ^{\textrm{2}} C, CAN, Ethernet, Profibus, 
Modbus, USB, SPI, JTAG ...), Media (IDE, Memory cards, 
eeprom, flash...), En-/Decryption, Remote debugging, 
Realtime kernel, Keyboard, LCD, RTC, FPGA, PID then the 
sdcc-user mailing list [http://sourceforge.net/mail/?group_id=599] would certainly like to hear 
about it. Programmers coding for embedded systems are 
not especially famous for being enthusiastic, so don't 
expect a big hurray but as the mailing list is 
searchable these references are very valuable. Let's 
help to create a climate where information is shared.

 Memory Models

 MCS51 Memory Models

 Small, Medium and Large

SDCC allows three memory models for MCS51 code, small, 
medium and large. Modules compiled with different 
memory models should never be combined together or the 
results would be unpredictable. The library routines 
supplied with the compiler are compiled as small, 
medium and large. The compiled library modules are 
contained in separate directories as small, medium and 
large so that you can link to the appropriate set.

When the medium or large model is used all variables 
declared without a storage class will be allocated into 
the external ram, this includes all parameters and 
local variables (for non-reentrant functions). When the 
small model is used variables without storage class are 
allocated in the internal ram.

Judicious usage of the processor specific storage classes
 and the 'reentrant' function type will yield much more 
efficient code, than using the large model. Several 
optimizations are disabled when the program is compiled 
using the large model, it is therefore recommended that 
the small model be used unless absolutely required.

 External Stack<sub:External-Stack>

The external stack (--xstack option) is located in pdata
 memory (usually at the start of the external ram 
segment) and uses all unused space in pdata (max. 256 
bytes). When --xstack option is used to compile the 
program, the parameters and local variables of all 
reentrant functions are allocated in this area. This 
option is provided for programs with large stack space 
requirements. When used with the --stack-auto option, 
all parameters and local variables are allocated on the 
external stack (note: support libraries will need to be 
recompiled with the same options. There is a predefined 
target in the library makefile).

The compiler outputs the higher order address byte of 
the external ram segment into port P2 (see also section [sub:MCS51-variants]
), therefore when using the External Stack option, this 
port may not be used by the application program.

 DS390 Memory Model

The only model supported is Flat 24. This generates 
code for the 24 bit contiguous addressing mode of the 
Dallas DS80C390 part. In this mode, up to four meg of 
external RAM or code space can be directly addressed. 
See the data sheets at www.dalsemi.com for further 
information on this part.

Note that the compiler does not generate any code to 
place the processor into 24 bitmode (although tinibios 
in the ds390 libraries will do that for you). If you 
don't use tinibios, the boot loader or similar code 
must ensure that the processor is in 24 bit contiguous 
addressing mode before calling the SDCC startup code.

Like the --model-large option, variables will by 
default be placed into the XDATA segment. 

Segments may be placed anywhere in the 4 meg address 
space using the usual --*-loc options. Note that if any 
segments are located above 64K, the -r flag must be 
passed to the linker to generate the proper segment 
relocations, and the Intel HEX output format must be 
used. The -r flag can be passed to the linker by using 
the option -Wl-r on the SDCC command line. However, 
currently the linker can not handle code segments > 64k.

 Pragmas

SDCC supports the following #pragma directives:

 save - this will save all current options to the 
  save/restore stack. See #pragma restore.

 restore - will restore saved options from the last 
  save. saves & restores can be nested. SDCC uses a 
  save/restore stack: save pushes current options to 
  the stack, restore pulls current options from the 
  stack. See #pragma save.
  

 callee_saves function1[,function2[,function3...]] - 
  The compiler by default uses a caller saves 
  convention for register saving across function calls, 
  however this can cause unnecessary register pushing & popping
   when calling small functions from larger functions. 
  This option can be used to switch off the register 
  saving convention for the function names specified. 
  The compiler will not save registers when calling 
  these functions, extra code need to be manually 
  inserted at the entry & exit for these functions to 
  save & restore the registers used by these functions, 
  this can SUBSTANTIALLY reduce code & improve run time 
  performance of the generated code. In the future the 
  compiler (with inter procedural analysis) may be able 
  to determine the appropriate scheme to use for each 
  function call. If --callee-saves command line option 
  is used, the function names specified in #pragma callee_saves
   is appended to the list of functions specified in 
  the command line.

 exclude none | {acc[,b[,dpl[,dph]]] - The exclude 
  pragma disables the generation of pairs of push/pop 
  instructions in Interrupt Service Routines. The 
  directive should be placed immediately before the ISR 
  function definition and it affects ALL ISR functions 
  following it. To enable the normal register saving 
  for ISR functions use #pragma exclude none. See also 
  the related keyword _naked.

 less_pedantic - the compiler will not warn you anymore 
  for obvious mistakes, you'r on your own now ;-(

 disable_warning <nnnn> - the compiler will not warn 
  you anymore about warning number <nnnn>.

 nogcse - will stop global common subexpression elimination.

 noinduction - will stop loop induction optimizations.

 noinvariant - will not do loop invariant 
  optimizations. For more details see Loop Invariants 
  in section[sub:Loop-Optimizations].

 noiv - Do not generate interrupt vector table entries 
  for all ISR functions defined after the pragma. This 
  is useful in cases where the interrupt vector table 
  must be defined manually, or when there is a 
  secondary, manually defined interrupt vector table 
  (e.g. for the autovector feature of the Cypress 
  EZ-USB FX2). More elegantly this can be achieved by 
  obmitting the optional interrupt number after the 
  interrupt keyword, see section [sub:Interrupt-Service-Routines] about interrupts.

 nojtbound - will not generate code for boundary value 
  checking, when switch statements are turned into 
  jump-tables (dangerous). For more details see section [sub:'switch'-Statements].

 noloopreverse - Will not do loop reversal optimization

 nooverlay - the compiler will not overlay the 
  parameters and local variables of a function.

 stackauto- See option --stack-auto and section [sec:Parameters-and-Local-Variables] 
  Parameters and Local Variables.

 opt_code_speed - The compiler will optimize code 
  generation towards fast code, possibly at the expense 
  of code size.

 opt_code_size - The compiler will optimize code 
  generation towards compact code, possibly at the 
  expense of code speed.

 opt_code_balanced - The compiler will attempt to 
  generate code that is both compact and fast, as long 
  as meeting one goal is not a detriment to the other 
  (this is the default). 

 std_sdcc89 - Generally follow the C89 standard, but 
  allow SDCC features that conflict with the standard (default).

 std_c89 - Follow the C89 standard and disable SDCC 
  features that conflict with the standard.

 std_sdcc99 - Generally follow the C99 standard, but 
  allow SDCC features that conflict with the standard 
  (incomplete support).

 std_c99 - Follow the C99 standard and disable SDCC 
  features that conflict with the standard (incomplete support).

 codeseg <name>- Use this name (max. 8 characters) for 
  the code segment.

 constseg <name>- Use this name (max. 8 characters) for 
  the const segment.

SDCPP supports the following #pragma directives:

 preproc_asm (+ | -) - switch _asm _endasm block 
  preprocessing on / off. Default is on.

The pragma's are intended to be used to turn-on or off 
certain optimizations which might cause the compiler to 
generate extra stack / data space to store compiler 
generated temporary variables. This usually happens in 
large functions. Pragma directives should be used as 
shown in the following example, they are used to 
control options & optimizations for a given function; 
pragmas should be placed before and/or after a 
function, placing pragma's inside a function body could 
have unpredictable results.

#pragma save        /* save the current settings */ 
#pragma nogcse      /* turnoff global subexpression 
elimination */ 
#pragma noinduction /* turn off induction optimizations 
*/ 
int foo () 
{ 
    ... 
    /* large code */ 
    ... 
} 
#pragma restore /* turn the optimizations back on */

The compiler will generate a warning message when extra 
space is allocated. It is strongly recommended that the 
save and restore pragma's be used when changing options 
for a function.

 Defines Created by the Compiler

The compiler creates the following #defines:


+--------------------------------------------+-------------------------------------------------------------------------------------------------+
|                  #define                   |                                           Description                                           |
+--------------------------------------------+-------------------------------------------------------------------------------------------------+
+--------------------------------------------+-------------------------------------------------------------------------------------------------+
|                   SDCC                     | this Symbol is always defined. Since version 2.5.6 it's this version number as an int (ex. 256) |
+--------------------------------------------+-------------------------------------------------------------------------------------------------+
| SDCC_mcs51 or SDCC_ds390 or SDCC_z80, etc  |                           depending on the model used (e.g.: -mds390                            |
+--------------------------------------------+-------------------------------------------------------------------------------------------------+
|   __mcs51, __ds390, __hc08, __z80, etc     |                            depending on the model used (e.g. -mz80)                             |
+--------------------------------------------+-------------------------------------------------------------------------------------------------+
|              SDCC_STACK_AUTO               |                                when --stack-auto option is used                                 |
+--------------------------------------------+-------------------------------------------------------------------------------------------------+
|             SDCC_MODEL_SMALL               |                                   when --model-small is used                                    |
+--------------------------------------------+-------------------------------------------------------------------------------------------------+
|             SDCC_MODEL_MEDIUM              |                                   when --model-medium is used                                   |
+--------------------------------------------+-------------------------------------------------------------------------------------------------+
|             SDCC_MODEL_LARGE               |                                   when --model-large is used                                    |
+--------------------------------------------+-------------------------------------------------------------------------------------------------+
|              SDCC_USE_XSTACK               |                                  when --xstack option is used                                   |
+--------------------------------------------+-------------------------------------------------------------------------------------------------+
|            SDCC_STACK_TENBIT               |                                      when -mds390 is used                                       |
+--------------------------------------------+-------------------------------------------------------------------------------------------------+
|             SDCC_MODEL_FLAT24              |                                      when -mds390 is used                                       |
+--------------------------------------------+-------------------------------------------------------------------------------------------------+


Notes on supported Processors

 MCS51 variants<sub:MCS51-variants>

MCS51 processors are available from many vendors and 
come in many different flavours. While they might 
differ considerably in respect to Special Function 
Registers the core MCS51 is usually not modified or is 
kept compatible. 

 pdata access by SFR 

With the upcome of devices with internal xdata and 
flash memory devices using port P2 as dedicated I/O 
port is becoming more popular. Switching the high byte 
for pdata access which was formerly done by port P2 is 
then achieved by a Special Function Register. In 
well-established MCS51 tradition the address of this 
sfr is where the chip designers decided to put it. 
Needless to say that they didn't agree on a common name 
either. So that the startup code can correctly 
initialize xdata variables, you should define an sfr 
with the name _XPAGE at the appropriate location if the 
default, port P2, is not used for this. Some examples are:

sfr at 0x92 _XPAGE; /* Cypress EZ-USB family */

sfr at 0xaf _XPAGE; /* some Silicon Labs (Cygnal) chips */

sfr at 0xaa _XPAGE; /* some Silicon Labs (Cygnal) chips */

For more exotic implementations further customizations 
may be needed. See section [sub:Startup-Code] for other possibilities.

 Other Features available by SFR

Some MCS51 variants offer features like Double DPTR, 
multiple DPTR, decrementing DPTR, 16x16 Multiply. These 
are currently not used for the MCS51 port. If you 
absolutely need them you can fall back to inline 
assembly or submit a patch to SDCC.

 DS400 port

The DS80C400 microcontroller has a rich set of 
peripherals. In its built-in ROM library it includes 
functions to access some of the features, among them is 
a TCP stack with IP4 and IP6 support. Library headers 
(currently in beta status) and other files are provided 
at [ftp://ftp.dalsemi.com/pub/tini/ds80c400/c_libraries/sdcc/index.html]. 

 The Z80 and gbz80 port

SDCC can target both the Zilog  and the Nintendo 
Gameboy's Z80-like gbz80. The Z80 port is passed 
through the same regressions tests as the MCS51 and 
DS390 ports, so floating point support, support for 
long variables and bitfield support is fine. See 
mailing lists and forums about interrupt routines.

As always, the code is the authoritative reference - 
see z80/ralloc.c and z80/gen.c. The stack frame is 
similar to that generated by the IAR Z80 compiler. IX 
is used as the base pointer, HL and IY are used as a 
temporary registers, and BC and DE are available for 
holding variables. Return values for the Z80 port are 
stored in L (one byte), HL (two bytes), or DEHL (four 
bytes). The gbz80 port use the same set of registers 
for the return values, but in a different order of 
significance: E (one byte), DE (two bytes), or HLDE 
(four bytes).

 The HC08 port

The port to the Motorola HC08 family has been added in 
October 2003, and is still undergoing some basic 
development. The code generator is complete, but the 
register allocation is still quite unoptimized. Some of 
the SDCC's standard C library functions have embedded 
non-HC08 inline assembly and so are not yet usable.



 The PIC14 port

The 14bit PIC port still requires a major effort from 
the development community. However it can work for very 
simple code.

 C code and 14bit PIC code page and RAM banks

The linker organizes allocation for the code page and 
RAM banks. It does not have intimate knowledge of the 
code flow. It will put all the code section of a single 
asm file into a single code page. In order to make use 
of multiple code pages, separate asm files must be 
used. The compiler treats all functions of a single C 
file as being in the same code page unless it is non 
static. The compiler treats all local variables of a 
single C file as being in the same RAM bank unless it 
is an extern.

To get the best follow these guide lines:

 make local functions static, as non static functions 
  require code page selection overhead.

 Make local variables static as extern variables 
  require RAM bank selection overhead.

 For devices that have multiple code pages it is more 
  efficient to use the same number of files as pages, 
  i.e. for the 16F877 use 4 separate files and i.e. for 
  the 16F874 use 2 separate files. This way the linker 
  can put the code for each file into different code 
  pages and the compiler can allocate reusable 
  variables more efficiently and there's less page 
  selection overhead. And as for any 8 bit micro 
  (especially for PIC 14 as they have a very simple 
  instruction set) use 'unsigned char' whereever 
  possible instead of 'int'.

 Creating a device include file 

For generating a device include file use the support 
perl script inc2h.pl kept in directory support/script.

 Interrupt code

For the interrupt function, use the keyword 'interrupt' 
with level number of 0 (PIC14 only has 1 interrupt so 
this number is only there to avoid a syntax error - it 
ought to be fixed). E.g.:

void Intr(void) interrupt 0
{
  T0IF = 0; /* Clear timer interrupt */
}

 Linking and assembling

For assembling you can use either GPUTILS' gpasm.exe or 
MPLAB's mpasmwin.exe. GPUTILS is available from [http://sourceforge.net/projects/gputils]. For 
linking you can use either GPUTIL's gplink or MPLAB's 
mplink.exe. If you use MPLAB and an interrupt function 
then the linker script file vectors section will need 
to be enlarged to link with mplink.

Here is a Makefile using GPUTILS:

.c.o:
        sdcc -S -V -mpic14 -p16F877 $< 
        gpasm -c $*.asm

$(PRJ).hex: $(OBJS) 
        gplink -m -s $(PRJ).lkr -o $(PRJ).hex $(OBJS) libsdcc.lib

Here is a Makefile using MPLAB:

.c.o: 
        sdcc -S -V -mpic14 -p16F877 $< 
        mpasmwin /q /o $*.asm

$(PRJ).hex: $(OBJS) 
        mplink /v $(PRJ).lkr /m $(PRJ).map /o $(PRJ).hex 
$(OBJS) libsdcc.lib

Please note that indentations within a Makefile have to 
be done with a tabulator character.

 Command-line options

Besides the switches common to all SDCC backends, the 
PIC14 port accepts the following options (for an 
updated list see sdcc --help):

--debug-extra emit debug info in assembly output

--no-pcode-opt disable (slightly faulty) optimization 
on pCode

 The library

 error: missing definition for symbol "__gptrget1"

The PIC14 port uses library routines to provide more 
complex operations like multiplication, 
division/modulus and (generic) pointer dereferencing. 
In order to add these routines to your project, you 
must link with PIC14's libsdcc.lib. For single source 
file projects this is done automatically, more complex 
projects must add libsdcc.lib to the linker's 
arguments. Make sure you also add an include path for 
the library (using the -I switch to the linker)!

 Processor mismatch in file "XXX".

This warning can usually be ignored due to the very 
good compatibility amongst 14 bit PIC devices.

You might also consider recompiling the library for 
your specific device by changing the ARCH=p16f877 
(default target) entry in device/lib/pic/Makefile.in 
and device/lib/pic/Makefile to reflect your device. 
This might even improve performance for smaller devices 
as unneccesary BANKSELs migth be removed.

 Known bugs

 initialized data

Currently, data can only be initialized if it resides 
in the source file together with main(). Data in other 
source files will silently not be initialized.

 The PIC16 port

The PIC16 port is the portion of SDCC that is 
responsible to produce code for the Microchip(TM) 
microcontrollers with 16 bit core. Currently this 
family of microcontrollers contains the PIC18Fxxx and 
PIC18Fxxxx. Currently supported devices are:

+----------+----------+----------+----------+----------+---------+
| 18F242   | 18F248   | 18F252   | 18F258   | 18F442   | 18F448  |
+----------+----------+----------+----------+----------+---------+
| 18F452   | 18F458   | 18F1220  | 18F2220  | 18F2550  | 18F4331 |
+----------+----------+----------+----------+----------+---------+
| 18F4455  | 18F6520  | 18F6620  | 18F6680  | 18F6720  | 18F8520 |
+----------+----------+----------+----------+----------+---------+
| 18F8620  | 18F8680  | 18F8720  |          |          |         |
+----------+----------+----------+----------+----------+---------+


 Global Options

PIC16 port supports the standard command line arguments 
as supposed, with the exception of certain cases that 
will be mentioned in the following list:

--callee-saves See --all-callee-saves

--all-callee-saves All function arguments are passed on 
stack by default. There is no need to specify this in 
the command line.

--fommit-frame-pointer Frame pointer will be omitted 
when the function uses no local variables.

 Port Specific Options

The port specific options appear after the global 
options in the sdcc --help output.

 General Options

General options enable certain port features and optimizations.

--stack-model=[model] Used in conjuction with the 
command above. Defines the stack model to be used, 
valid stack models are : 

  small Selects small stack model. 8 bit stack and 
  frame pointers. Supports 256 bytes stack size.

  large Selects large stack model. 16 bit stack and 
  frame pointers. Supports 65536 bytes stack size.

--preplace-udata-with=[kword] Replaces the default 
udata keyword for allocating unitialized data variables 
with [kword]. Valid keywords are: "udata_acs", 
"udata_shr", "udata_ovr".

--ivt-loc <nnnn> positions the Interrupt Vector Table 
at location <nnnn>. Useful for bootloaders.

--asm= sets the full path and name of an external 
assembler to call.

--link= sets the full path and name of an external 
linker to call.

--mplab-comp MPLAB compatibility option. Currently only 
suppresses special gpasm directives.

 Optimization Options

--optimize-goto Try to use (conditional) BRA instead of GOTO

--optimize-cmp Try to optimize some compares.

--optimize-df Analyze the dataflow of the generated 
code and improve it.

--obanksel=nn Set optimization level for inserting BANKSELs.


  0 no optimization

  1 checks previous used register and if it is the same 
  then does not emit BANKSEL, accounts only for labels.

  2 tries to check the location of (even different) 
  symbols and removes BANKSELs if they are in the same 
  bank. 
  Important: There might be problems if the linker 
  script has data sections across bank borders!

 Linking Options

--nodefaultlibs do not link default libraries when linking

--no-crt Don't link the default run-time modules

--use-crt= Use a custom run-time module instead of the defaults.

 Debugging Options

Debugging options enable extra debugging information in 
the output files.

--debug-xtra Similar to --debug, but dumps more information.

--debug-ralloc Force register allocator to dump 
<source>.d file with debugging information. <source> is 
the name of the file compiled.

--pcode-verbose Enable pcode debugging information in 
translation.

--denable-peeps Force the usage of peepholes. Use with care.

--gstack Trace push/pops for stack pointer overflow

--call-tree dump call tree in .calltree file

 Enviromental Variables

There is a number of enviromental variables that can be 
used when running SDCC to enable certain optimizations 
or force a specific program behaviour. these variables 
are primarily for debugging purposes so they can be 
enabled/disabled at will.

Currently there is only two such variables available:

OPTIMIZE_BITFIELD_POINTER_GET when this variable exists 
reading of structure bitfields is optimized by directly 
loading FSR0 with the address of the bitfield 
structure. Normally SDCC will cast the bitfield 
structure to a bitfield pointer and then load FSR0. 
This step saves data ram and code space for functions 
that perform heavy use of bitfields. (ie. 80 bytes of 
code space are saved when compiling malloc.c with this 
option). 

NO_REG_OPT do not perform pCode registers optimization. 
This should be used for debugging purposes. In some 
where bugs in the pcode optimizer are found, users can 
benefit from temporarily disabling the optimizer until 
the bug is fixed.

 Preprocessor Macros

PIC16 port defines the following preprocessor macros 
while translating a source.

+------------------+-----------------------------------------------------------------------------------------+
|      Macro       |                                       Description                                       |
+------------------+-----------------------------------------------------------------------------------------+
+------------------+-----------------------------------------------------------------------------------------+
|   SDCC_pic16     |                                   Port identification                                   |
+------------------+-----------------------------------------------------------------------------------------+
|     __pic16      |                           Port identification (same as above)                           |
+------------------+-----------------------------------------------------------------------------------------+
|   pic18fxxxx     | MCU Identification. xxxx is the microcontrol identification number, i.e. 452, 6620, etc |
+------------------+-----------------------------------------------------------------------------------------+
|    __18Fxxxx     |                           MCU Identification (same as above)                            |
+------------------+-----------------------------------------------------------------------------------------+
| STACK_MODEL_nnn  |           nnn = SMALL or LARGE respectively according to the stack model used           |
+------------------+-----------------------------------------------------------------------------------------+


In addition the following macros are defined when 
calling assembler:

+------------------+-----------------------------------------------------------------------------------------+
|      Macro       |                                       Description                                       |
+------------------+-----------------------------------------------------------------------------------------+
+------------------+-----------------------------------------------------------------------------------------+
|    __18Fxxxx     | MCU Identification. xxxx is the microcontrol identification number, i.e. 452, 6620, etc |
+------------------+-----------------------------------------------------------------------------------------+
| SDCC_MODEL_nnn   |      nnn = SMALL or LARGE respectively according to the memory model used for SDCC      |
+------------------+-----------------------------------------------------------------------------------------+
| STACK_MODEL_nnn  |           nnn = SMALL or LARGE respectively according to the stack model used           |
+------------------+-----------------------------------------------------------------------------------------+


 Directories

PIC16 port uses the following directories for searching 
header files and libraries.

+----------------------------+--------------------------+------------+----------------+
|         Directory          |       Description        |   Target   | Command prefix |
+----------------------------+--------------------------+------------+----------------+
+----------------------------+--------------------------+------------+----------------+
| PREFIX/sdcc/include/pic16  |  PIC16 specific headers  |  Compiler  |       -I       |
+----------------------------+--------------------------+------------+----------------+
|   PREFIX/sdcc/lib/pic16    | PIC16 specific libraries |   Linker   |       -L       |
+----------------------------+--------------------------+------------+----------------+


 Pragmas<sub:PIC16_Pragmas>

PIC16 port currently supports the following pragmas:

stack pragma stack forces the code generator to 
initialize the stack & frame pointers at a specific 
address. This is an adhoc solution for cases where no 
STACK directive is available in the linker script or 
gplink is not instructed to create a stack section.
The stack pragma should be used only once in a project. 
Multiple pragmas may result in indeterminate behaviour 
of the program.The old format (ie. #pragma stack 0x5ff) is deprecated 
and will cause the stack pointer to cross page 
boundaries (or even exceed the available data RAM) and 
crash the program. Make sure that stack does not cross 
page boundaries when using the SMALL stack model.
The format is as follows:

#pragma stack bottom_address [stack_size]

bottom_address is the lower bound of the stack section. 
The stack pointer initially will point at address 
(bottom_address+stack_size-1).

Example:



/* initializes stack of 100 bytes at RAM address 0x200 */

#pragma stack 0x200 100

If the stack_size field is omitted then a stack is 
created with the default size of 64. This size might be 
enough for most programs, but its not enough for 
operations with deep function nesting or excessive 
stack usage.

wparam This pragma is deprecated. Its use will cause a 
warning message to be issued.


code place a function symbol at static FLASH address

Example:



/* place function test_func at 0x4000 */

#pragma code test_func 0x4000



library instructs the linker to use a library module.
Usage:

#pragma library module_name

module_name can be any library or object file 
(including its path). Note that there are four reserved 
keywords which have special meaning. These are:

+----------+-----------------------------+----------------+
| Keyword  | Description                 | Module to link |
+----------+-----------------------------+----------------+
+----------+-----------------------------+----------------+
| ignore   | ignore all library pragmas  | (none)         |
+----------+-----------------------------+----------------+
|    c     | link the C library          | libc18f.lib    |
+----------+-----------------------------+----------------+
|  math    | link the Math libarary      | libm18f.lib    |
+----------+-----------------------------+----------------+
|   io     | link the I/O library        | libio18f*.lib  |
+----------+-----------------------------+----------------+
|  debug   | link the debug library      | libdebug.lib   |
+----------+-----------------------------+----------------+

* is the device number, i.e. 452 for PIC18F452 MCU.

This feature allows for linking with specific libraries 
withoug having to explicit name them in the command 
line. Note that the ignore keyword will reject all 
modules specified by the library pragma.

udata pragma udata instructs the compiler to emit code 
so that linker will place a variable at a specific 
memory bank

Example:



/* places variable foo at bank2 */

#pragma udata bank2 foo

char foo;

In order for this pragma to work extra SECTION 
directives should be added in the .lkr script. In the 
following example a sample .lkr file is shown:



// Sample linker script for the PIC18F452 processor

LIBPATH .

CODEPAGE   NAME=vectors    START=0x0            
END=0x29           PROTECTED

CODEPAGE   NAME=page       START=0x2A           END=0x7FFF

CODEPAGE   NAME=idlocs     START=0x200000       
END=0x200007       PROTECTED

CODEPAGE   NAME=config     START=0x300000       
END=0x30000D       PROTECTED

CODEPAGE   NAME=devid      START=0x3FFFFE       
END=0x3FFFFF       PROTECTED

CODEPAGE   NAME=eedata     START=0xF00000       
END=0xF000FF       PROTECTED

ACCESSBANK NAME=accessram  START=0x0            END=0x7F



DATABANK   NAME=gpr0       START=0x80           END=0xFF

DATABANK   NAME=gpr1       START=0x100          END=0x1FF

DATABANK   NAME=gpr2       START=0x200          END=0x2FF

DATABANK   NAME=gpr3       START=0x300          END=0x3FF

DATABANK   NAME=gpr4       START=0x400          END=0x4FF

DATABANK   NAME=gpr5       START=0x500          END=0x5FF

ACCESSBANK NAME=accesssfr  START=0xF80          
END=0xFFF          PROTECTED



SECTION    NAME=CONFIG     ROM=config



SECTION    NAME=bank0      RAM=gpr0       # these 
SECTION directives

SECTION    NAME=bank1      RAM=gpr1       # should be 
added to link

SECTION    NAME=bank2      RAM=gpr2       # section 
name 'bank?' with

SECTION    NAME=bank3      RAM=gpr3       # a specific 
DATABANK name

SECTION    NAME=bank4      RAM=gpr4

SECTION    NAME=bank5      RAM=gpr5

The linker will recognise the section name set in the 
pragma statement and will position the variable at the 
memory bank set with the RAM field at the SECTION line 
in the linker script file.

 Header Files<sub:PIC16_Header-Files>

There is one main header file that can be included to 
the source files using the pic16 port. That file is the 
pic18fregs.h. This header file contains the definitions 
for the processor special registers, so it is necessary 
if the source accesses them. It can be included by 
adding the following line in the beginning of the file:

#include <pic18fregs.h>

The specific microcontroller is selected within the 
pic18fregs.h automatically, so the same source can be 
used with a variety of devices.

 Libraries

The libraries that PIC16 port depends on are the 
microcontroller device libraries which contain the 
symbol definitions for the microcontroller special 
function registers. These libraries have the format 
pic18fxxxx.lib, where xxxx is the microcontroller 
identification number. The specific library is selected 
automatically by the compiler at link stage according 
to the selected device.

Libraries are created with gplib which is part of the 
gputils package [http://sourceforge.net/projects/gputils].

 Building the libraries

Before using SDCC/pic16 there are some libraries that 
need to be compiled. This process is not done 
automatically by SDCC since not all users use SDCC for 
pic16 projects. So each user should compile the 
libraries separately.

The steps to compile the pic16 libraries under Linux are:

cd device/lib/pic16

./configure

make

cd ..

make model-pic16

su -c 'make install'     # install the libraries, you 
need the root password

If you need to install the headers too, do:

cd device/include

su -c 'make install'     # install the headers, you 
need the root password

There exist a special target to build the I/O 
libraries. This target is not automatically build 
because it will build the I/O library for every 
supported device. This way building will take quite a 
lot of time. Users are advised to edit the 
device/lib/pic16/pics.build file and then execute:

make lib-io

 Memory Models

The following memory models are supported by the PIC16 port:

 small model

 large model

Memory model affects the default size of pointers 
within the source. The sizes are shown in the next table:

+-----------------------------------------++--------------+-------------+
| Pointer sizes according to memory model || small model  | large model |
+-----------------------------------------++--------------+-------------+
+-----------------------------------------++--------------+-------------+
|              code pointers              ||   16-bits    |   24-bits   |
+-----------------------------------------+               +-------------+
+-----------------------------------------++--------------+-------------+
|              data pointers              ||   16-bits    |   16-bits   |
+-----------------------------------------++--------------+-------------+


It is advisable that all sources within a project are 
compiled with the same memory model. If one wants to 
override the default memory model, this can be done by 
declaring a pointer as far or near. Far selects large 
memory model's pointers, while near selects small 
memory model's pointers.

The standard device libraries (see [sub:PIC16_Header-Files]) contain no 
reference to pointers, so they can be used with both 
memory models.

 Stack

The stack implementation for the PIC16 port uses two 
indirect registers, FSR1 and FSR2.

FSR1 is assigned as stack pointer

FSR2 is assigned as frame pointer

The following stack models are supported by the PIC16 port

 small model

 large model

Small model means that only the FSRxL byte is used to 
access stack and frame, while large uses both FSRxL and 
FSRxH registers. The following table shows the 
stack/frame pointers sizes according to stack model and 
the maximum space they can address:

+------------------------------------------------------++---------+---------+
| Stack & Frame pointer sizes according to stack model || small   |  large  |
+------------------------------------------------------++---------+---------+
+------------------------------------------------------++---------+---------+
|                  Stack pointer FSR1                  || 8-bits  | 16-bits |
+------------------------------------------------------++---------+---------+
|                  Frame pointer FSR2                  || 8-bits  | 16-bits |
+------------------------------------------------------++---------+---------+


Large stack model is currently not working properly 
throughout the code generator. So its use is not 
advised. Also there are some other points that need 
special care:


 Do not create stack sections with size more than one 
  physical bank (that is 256 bytes)

 Stack sections should no cross physical bank limits 
  (i.e. #pragma stack 0x50 0x100)

These limitations are caused by the fact that only 
FSRxL is modified when using SMALL stack model, so no 
more than 256 bytes of stack can be used. This problem 
will disappear after LARGE model is fully implemented.

 Functions

In addition to the standard SDCC function keywords, 
PIC16 port makes available two more:

wparam Use the WREG to pass one byte of the first 
function argument. This improves speed but you may not 
use this for functions with arguments that are called 
via function pointers, otherwise the first byte of the 
first parameter will get lost. Usage:

void func_wparam(int a) wparam

{

    /* WREG hold the lower part of a */

    /* the high part of a is stored in FSR2+2 (or +3 
for large stack model) */

...

}

This keyword replaces the deprecated wparam pragma.

shadowregs When entering/exiting an ISR, it is possible 
to take advantage of the PIC18F hardware shadow 
registers which hold the values of WREG, STATUS and BSR 
registers. This can be done by adding the keyword 
shadowregs before the interrupt keyword in the 
function's header.

void isr_shadow(void) shadowregs interrupt 1

{

...

}

shadowregs instructs the code generator not to 
store/restore WREG, STATUS, BSR when entering/exiting 
the ISR.

 Function return values

Return values from functions are placed to the 
appropriate registers following a modified Microchip 
policy optimized for SDCC. The following table shows 
these registers:

+-----------+----------------------------------------+
|   size    |          destination register          |
+-----------+----------------------------------------+
+-----------+----------------------------------------+
|  8 bits   |                  WREG                  |
+-----------+----------------------------------------+
| 16 bits   |               PRODL:WREG               |
+-----------+----------------------------------------+
| 24 bits   |            PRODH:PRODL:WREG            |
+-----------+----------------------------------------+
| 32 bits   |         FSR0L:PRODH:PRODL:WREG         |
+-----------+----------------------------------------+
| >32 bits  | on stack, FSR0 points to the beginning |
+-----------+----------------------------------------+


 Interrupts

An interrupt servive routine (ISR) is declared using 
the interrupt keyword.

void isr(void) interrupt n

{

...

}

n is the interrupt number, which for PIC18F devices can be:

+----+---------------------------+--------------------------+
| n  |     Interrupt Vector      | Interrupt Vector Address |
+----+---------------------------+--------------------------+
+----+---------------------------+--------------------------+
| 0  |       RESET vector        |         0x000000         |
+----+---------------------------+--------------------------+
| 1  | HIGH priority interrupts  |         0x000008         |
+----+---------------------------+--------------------------+
| 2  | LOW priority interrupts   |         0x000018         |
+----+---------------------------+--------------------------+


When generating assembly code for ISR the code 
generator places a goto instruction at the Interrupt 
Vector Address which points at the genetated ISR. This 
single GOTO instruction is part of an automatically 
generated interrupt entry point function. The actuall 
ISR code is placed as normally would in the code space. 
Upon interrupt request, the GOTO instruction is 
executed which jumps to the ISR code. When declaring 
interrupt functions as _naked this GOTO instruction is 
not generated. The whole interrupt functions is 
therefore placed at the Interrupt Vector Address of the 
specific interrupt. This is not a problem for the LOW 
priority interrupts, but it is a problem for the RESET 
and the HIGH priority interrupts because code may be 
written at the next interrupts vector address and 
cause undeterminate program behaviour if that interrupt 
is raised.This is not a problem when

 this is a HIGH interrupt ISR and LOW interrupts are 
  disabled or not used.

 when the ISR is small enough not to reach the next 
  interrupts vector address.

n is possible to be omitted. This way a function is 
generated similar to an ISR, but it is not assigned to 
any interrupt.

When entering an interrupt, currently the PIC16 port 
automatically saves the following registers:

 WREG

 STATUS

 BSR

 PROD (PRODL and PRODH)

 FSR0 (FSR0L and FSR0H)

These registers are restored upon return from the 
interrupt routine.NOTE that when the _naked attribute is specified for an 
interrupt routine, then NO registers are stored or restored.

 Generic Pointers

Generic pointers are implemented in PIC16 port as 
3-byte (24-bit) types. There are 3 types of generic 
pointers currently implemented data, code and eeprom 
pointers. They are differentiated by the value of the 
7th and 6th bits of the upper byte:

+-----------------+-----------+---------+-----------------------------------------------------------------------+
|  pointer type   |  7th bit  | 6th bit |    rest of the pointer       descrption                               |
+-----------------+-----------+---------+-----------------------------------------------------------------------+
+-----------------+-----------+---------+-----------------------------------------------------------------------+
|      data       |     1     |    0    |  uuuuuu uuuuxxxx xxxxxxxx    a 12-bit data pointer in data RAM memory |
+-----------------+-----------+---------+-----------------------------------------------------------------------+
|      code       |     0     |    0    |  uxxxxx xxxxxxxx xxxxxxxx    a 21-bit code pointer in FLASH memory    |
+-----------------+-----------+---------+-----------------------------------------------------------------------+
|     eeprom      |     0     |    1    |  uuuuuu uuuuuuxx xxxxxxxx    a 10-bit eeprom pointer in EEPROM memory |
+-----------------+-----------+---------+-----------------------------------------------------------------------+
| (unimplemented) |     1     |    1    |  xxxxxx xxxxxxxx xxxxxxxx    unimplemented pointer type               |
+-----------------+-----------+---------+-----------------------------------------------------------------------+


Generic pointer are read and written with a set of 
library functions which read/write 1, 2, 3, 4 bytes.

 PIC16 C Libraries

 Standard I/O Streams

In the stdio.h the type FILE is defined as:

typedef char * FILE;

This type is the stream type implemented I/O in the 
PIC18F devices. Also the standard input and output 
streams are declared in stdio.h:

extern FILE * stdin;

extern FILE * stdout;

The FILE type is actually a generic pointer which 
defines one more type of generic pointers, the stream 
pointer. This new type has the format:

+--------------+---------+------+------+-------+-----------------------------------------------------------------------------+
| pointer type |  <7:6>  | <5>  | <4>  | <3:0> |  rest of the pointer    descrption                                          |
+--------------+---------+------+------+-------+-----------------------------------------------------------------------------+
+--------------+---------+------+------+-------+-----------------------------------------------------------------------------+
|    stream    |   00    |  1   |  0   | nnnn  |   uuuuuuuu uuuuuuuu     upper byte high nubble is 0x2n, the rest are zeroes |
+--------------+---------+------+------+-------+-----------------------------------------------------------------------------+


Currently implemented there are 3 types of streams defined:

+---------------+-------------+---------+----------------------------------------------------+
| stream type   |   value     | module  |                    description                     |
+---------------+-------------+---------+----------------------------------------------------+
+---------------+-------------+---------+----------------------------------------------------+
| STREAM_USART  | 0x200000UL  | USART   |  Writes/Reads characters via the USART peripheral  |
+---------------+-------------+---------+----------------------------------------------------+
| STREAM_MSSP   | 0x210000UL  |  MSSP   |  Writes/Reads characters via the MSSP peripheral   |
+---------------+-------------+---------+----------------------------------------------------+
| STREAM_USER   | 0x2f0000UL  | (none)  | Writes/Reads characters via used defined functions |
+---------------+-------------+---------+----------------------------------------------------+


The stream identifiers are declared as macros in the 
stdio.h header.

In the libc library there exist the functions that are 
used to write to each of the above streams. These are

__stream_usart_putchar writes a character at the USART stream

__stream_mssp_putchar writes a character at the MSSP stream

putchar dummy function. This writes a character to a 
user specified manner.

In order to increase performance putchar is declared in 
stdio.h as having its parameter in WREG (it has the 
wparam keyword). In stdio.h exists the macro 
PUTCHAR(arg) that defines the putchar function in a 
user-friendly way. arg is the name of the variable that 
holds the character to print. An example follows:

#include <pic18fregs.h>
#include <stdio.h>

PUTCHAR( c )

{

    PORTA = c;    /* dump character c to PORTA */

} 

void main(void)

{

    stdout = STREAM_USER;    /* this is not necessery, 
since stdout points

                              * by default to 
STREAM_USER */

    printf (This is a printf test\n);

}



 Printing functions

PIC16 contains an implementation of the printf-family 
of functions. There exist the following functions:

extern unsigned int sprintf(char *buf, char *fmt, ...);

extern unsigned int vsprintf(char *buf, char *fmt, 
va_list ap);



extern unsigned int printf(char *fmt, ...);

extern unsigned int vprintf(char *fmt, va_lista ap);



extern unsigned int fprintf(FILE *fp, char *fmt, ...);

extern unsigned int vfprintf(FILE *fp, char *fmt, 
va_list ap);

For sprintf and vsprintf buf should normally be a data 
pointer where the resulting string will be placed. No 
range checking is done so the user should allocate the 
necessery buffer. For fprintf and vfprintf fp should be 
a stream pointer (i.e. stdout, STREAM_MSSP, etc...).

 Signals

The PIC18F family of microcontrollers supports a number 
of interrupt sources. A list of these interrupts is 
shown in the following table:

+--------------+----------------------------++--------------+---------------------------------------+
| signal name  |        description         || signal name  |              descritpion              |
+--------------+----------------------------++--------------+---------------------------------------+
+--------------+----------------------------++--------------+---------------------------------------+
| SIG_RB       |   PORTB change interrupt   || SIG_EE       | EEPROM/FLASH write complete interrupt |
+--------------+----------------------------++--------------+---------------------------------------+
| SIG_INT0     |  INT0 external interrupt   || SIG_BCOL     |        Bus collision interrupt        |
+--------------+----------------------------++--------------+---------------------------------------+
| SIG_INT1     |  INT1 external interrupt   || SIG_LVD      |     Low voltage detect interrupt      |
+--------------+----------------------------++--------------+---------------------------------------+
| SIG_INT2     |  INT2 external interrupt   || SIG_PSP      |     Parallel slave port interrupt     |
+--------------+----------------------------++--------------+---------------------------------------+
| SIG_CCP1     |   CCP1 module interrupt    || SIG_AD       |   AD convertion complete interrupt    |
+--------------+----------------------------++--------------+---------------------------------------+
| SIG_CCP2     |   CCP2 module interrupt    || SIG_RC       |        USART receive interrupt        |
+--------------+----------------------------++--------------+---------------------------------------+
| SIG_TMR0     |  TMR0 overflow interrupt   || SIG_TX       |       USART transmit interrupt        |
+--------------+----------------------------++--------------+---------------------------------------+
| SIG_TMR1     |  TMR1 overflow interrupt   || SIG_MSSP     |    SSP receive/transmit interrupt     |
+--------------+----------------------------++--------------+---------------------------------------+
| SIG_TMR2     | TMR2 matches PR2 interrupt ||              |                                       |
+--------------+----------------------------++--------------+---------------------------------------+
| SIG_TMR3     |  TMR3 overflow interrupt   ||              |                                       |
+--------------+----------------------------++--------------+---------------------------------------+


The prototypes for these names are defined in the 
header file signal.h .

In order to simplify signal handling, a number of 
macros is provided:

DEF_INTHIGH(name) begin the definition of the interrupt 
dispatch table for high priority interrupts. name is 
the function name to use.

DEF_INTLOW(name) begin the definition of the interrupt 
dispatch table fo low priority interrupt. name is the 
function name to use.

DEF_HANDLER(sig,handler) define a handler for signal sig.

END_DEF end the declaration of the dispatch table.

Additionally there are two more macros to simplify the 
declaration of the signal handler:

SIGHANDLER(handler) this declares the function 
prototype for the handler function.

SIGHANDLERNAKED(handler) same as SIGHANDLER() but 
declares a naked function.

An example of using the macros above is shown below:

#include <pic18fregs.h>

#include <signal.h>

DEF_INTHIGH(high_int)

DEF_HANDLER(SIG_TMR0, _tmr0_handler)

DEF_HANDLER(SIG_BCOL, _bcol_handler)

END_DEF

SIGHANDLER(_tmr0_handler)

{

  /* action to be taken when timer 0 overflows */

}

SIGHANDLERNAKED(_bcol_handler)

{

  _asm

    /* action to be taken when bus collision occurs */

    retfie

 _endasm;

}

NOTES: Special care should be taken when using the 
above scheme:

 do not place a colon (;) at the end of the DEF_* and 
  END_DEF macros.

 when declaring SIGHANDLERNAKED handler never forget to 
  use retfie for proper returning.

 PIC16 Port -- Tips

Here you can find some general tips for compiling 
programs with SDCC/pic16.

 Stack size

The default stack size (that is 64 bytes) probably is 
enough for many programs. One must take care that when 
there are many levels of function nesting, or there is 
excessive usage of stack, its size should be extended. 
An example of such a case is the printf/sprintf family 
of functions. If you encounter problems like not being 
able to print integers, then you need to set the stack 
size around the maximum (256 for small stack model). 
The following diagram shows what happens when calling 
printf to print an integer:

printf () --> ltoa () --> ultoa () --> divschar ()

It is should be understood that stack is easily 
consumed when calling complicated functions. Using 
command line arguments like --fommit-frame-pointer 
might reduce stack usage by not creating unnecessery 
stack frames. Other ways to reduce stack usage may exist.

Debugging with SDCDB<cha:Debugging-with-SDCDB> 

SDCC is distributed with a source level debugger. The 
debugger uses a command line interface, the command 
repertoire of the debugger has been kept as close to gdb
 (the GNU debugger) as possible. The configuration and 
build process is part of the standard compiler 
installation, which also builds and installs the 
debugger in the target directory specified during 
configuration. The debugger allows you debug BOTH at 
the C source and at the ASM source level. Sdcdb is 
currently not available on Win32 platforms.

 Compiling for Debugging

The --debug option must be specified for all files for 
which debug information is to be generated. The 
complier generates a .adb file for each of these files. 
The linker creates the .cdb file from the .adb files 
and the address information. This .cdb is used by the debugger.

 How the Debugger Works

When the --debug option is specified the compiler 
generates extra symbol information some of which are 
put into the assembler source and some are put into the 
.adb file.  Then the linker creates the .cdb file from 
the individual .adb files with the address information 
for the symbols. The debugger reads the symbolic 
information generated by the compiler & the address 
information generated by the linker. It uses the 
SIMULATOR (Daniel's S51) to execute the program, the 
program execution is controlled by the debugger. When a 
command is issued for the debugger, it translates it 
into appropriate commands for the simulator.

 Starting the Debugger

The debugger can be started using the following command 
line. (Assume the file you are debugging has the file 
name foo).

sdcdb foo

The debugger will look for the following files.

 foo.c - the source file.

 foo.cdb - the debugger symbol information file.

 foo.ihx - the Intel hex format object file.

 Command Line Options

 --directory=<source file directory> this option can 
  used to specify the directory search list. The 
  debugger will look into the directory list specified 
  for source, cdb & ihx files. The items in the 
  directory list must be separated by ':', e.g. if the 
  source files can be in the directories /home/src1 and 
  /home/src2, the --directory option should be -
  -directory=/home/src1:/home/src2. Note there can be 
  no spaces in the option. 

 -cd <directory> - change to the <directory>.

 -fullname - used by GUI front ends.

 -cpu <cpu-type> - this argument is passed to the 
  simulator please see the simulator docs for details.

 -X <Clock frequency > this options is passed to the 
  simulator please see the simulator docs for details.

 -s <serial port file> passed to simulator see the 
  simulator docs for details.

 -S <serial in,out> passed to simulator see the 
  simulator docs for details.

 -k <port number> passed to simulator see the simulator 
  docs for details.

 Debugger Commands

As mentioned earlier the command interface for the 
debugger has been deliberately kept as close the GNU 
debugger gdb, as possible. This will help the 
integration with existing graphical user interfaces 
(like ddd, xxgdb or xemacs) existing for the GNU 
debugger. If you use a graphical user interface for the 
debugger you can skip this section.

 break [line | file:line | function | file:function]

Set breakpoint at specified line or function:

sdcdb>break 100 
sdcdb>break foo.c:100
sdcdb>break funcfoo
sdcdb>break foo.c:funcfoo

 clear [line | file:line | function | file:function ]

Clear breakpoint at specified line or function:

sdcdb>clear 100
sdcdb>clear foo.c:100
sdcdb>clear funcfoo
sdcdb>clear foo.c:funcfoo

 continue

Continue program being debugged, after breakpoint.

 finish

Execute till the end of the current function.

 delete [n]

Delete breakpoint number 'n'. If used without any 
option clear ALL user defined break points.

 info [break | stack | frame | registers ]

 info break - list all breakpoints

 info stack - show the function call stack.

 info frame - show information about the current 
  execution frame.

 info registers - show content of all registers.

 step

Step program until it reaches a different source line. 
Note: pressing <return> repeats the last command.

 next

Step program, proceeding through subroutine calls.

 run

Start debugged program.

 ptype variable 

Print type information of the variable.

 print variable

print value of variable.

 file filename

load the given file name. Note this is an alternate 
method of loading file for debugging.

 frame

print information about current frame.

 set srcmode

Toggle between C source & assembly source.

 ! simulator command

Send the string following '!' to the simulator, the 
simulator response is displayed. Note the debugger does 
not interpret the command being sent to the simulator, 
so if a command like 'go' is sent the debugger can 
loose its execution context and may display incorrect values.

 quit

"Watch me now. Iam going Down. My name is Bobby Brown"

 Interfacing with DDD

The screenshot was converted from png to eps with: "
bmeps -c -e8f -p3 ddd_example.png >ddd_example.eps" 
which produces a pretty compact eps file which is free 
from compression artifacts.

The screenshot was included in sdccman.lyx cvs version 
1.120 but later removed as this broke the build system 
on Sourceforge (pdf-file was broken).

The .eps File [http://svn.sourceforge.net/viewcvs.cgi/*checkout*/sdcc/trunk/sdcc/doc/figures/ddd_example.eps] shows a screenshot of a debugging 
session with DDD (Unix only) on a simulated 8032. The 
debugging session might not run as smoothly as the 
screenshot suggests. The debugger allows setting of 
breakpoints, displaying and changing variables, single 
stepping through C and assembler code. 
The source was compiled with 

sdcc --debug ddd_example.c 

and DDD was invoked with 

ddd -debugger 'sdcdb -cpu 8032 ddd_example'

 Interfacing with XEmacs

Two files (in emacs lisp) are provided for the 
interfacing with XEmacs, sdcdb.el and sdcdbsrc.el. 
These two files can be found in the $(prefix)/bin 
directory after the installation is complete. These 
files need to be loaded into XEmacs for the interface 
to work. This can be done at XEmacs startup time by 
inserting the following into your '.xemacs' file (which 
can be found in your HOME directory): 

(load-file sdcdbsrc.el) 

.xemacs is a lisp file so the () around the command is 
REQUIRED. The files can also be loaded dynamically 
while XEmacs is running, set the environment variable 
'EMACSLOADPATH' to the installation bin directory 
(<installdir>/bin), then enter the following command 
ESC-x load-file sdcdbsrc. To start the interface enter 
the following command: 

ESC-x sdcdbsrc

You will prompted to enter the file name to be 
debugged. 

The command line options that are passed to the 
simulator directly are bound to default values in the 
file sdcdbsrc.el. The variables are listed below, these 
values maybe changed as required.

 sdcdbsrc-cpu-type '51

 sdcdbsrc-frequency '11059200

 sdcdbsrc-serial nil

The following is a list of key mapping for the debugger 
interface.

 
;; Current Listing :: 
;;key              binding                      Comment 
;;---              -------                      -------
;; 
;; n               sdcdb-next-from-src          SDCDB next command 
;; b               sdcdb-back-from-src          SDCDB back command 
;; c               sdcdb-cont-from-src          SDCDB continue command
;; s               sdcdb-step-from-src          SDCDB step command 
;; ?               sdcdb-whatis-c-sexp          SDCDB ptypecommand for data at 
;;                                               buffer point 
;; x               sdcdbsrc-delete              SDCDB Delete all breakpoints if no 
arg 
;;                                               given or delete arg (C-u arg x) 
;; m               sdcdbsrc-frame               SDCDB Display current frame if no arg, 
;;                                               given or display frame arg 
;;                                               buffer point 
;; !               sdcdbsrc-goto-sdcdb          Goto the SDCDB output buffer 
;; p               sdcdb-print-c-sexp           SDCDB print command for data at 
;;                                               buffer point 
;; g               sdcdbsrc-goto-sdcdb          Goto the SDCDB output buffer 
;; t               sdcdbsrc-mode                Toggles Sdcdbsrc mode (turns it off) 
;; 
;; C-c C-f         sdcdb-finish-from-src        SDCDB finish command 
;; 
;; C-x SPC         sdcdb-break                  Set break for line with point 
;; ESC t           sdcdbsrc-mode                Toggle Sdcdbsrc mode 
;; ESC m           sdcdbsrc-srcmode             Toggle list mode 
;; 


TIPS

Here are a few guidelines that will help the compiler 
generate more efficient code, some of the tips are 
specific to this compiler others are generally good 
programming practice.

 Use the smallest data type to represent your 
  data-value. If it is known in advance that the value 
  is going to be less than 256 then use an 'unsigned 
  char' instead of a 'short' or 'int'. Please note, 
  that ANSI C requires both signed and unsigned chars 
  to be promoted to 'signed int' before doing any 
  operation. This promotion can be omitted, if the 
  result is the same. The effect of the promotion rules 
  together with the sign-extension is often surprising:

  unsigned char uc = 0xfe;
  if (uc * uc < 0) /* this is true! */
  {
      ....
  }

  uc * uc is evaluated as (int) uc * (int) uc = (int) 
  0xfe * (int) 0xfe = (int) 0xfc04 = -1024. 
  Another one:

  (unsigned char) -12 / (signed char) -3 = ...

  No, the result is not 4:

  (int) (unsigned char) -12 / (int) (signed char) -3 =
  (int) (unsigned char) 0xf4 / (int) (signed char) 0xfd =
  (int) 0x00f4 / (int) 0xfffd =
  (int) 0x00f4 / (int) 0xfffd =
  (int) 244 / (int) -3 =
  (int) -81 = (int) 0xffaf;

  Don't complain, that gcc gives you a different 
  result. gcc uses 32 bit ints, while SDCC uses 16 bit 
  ints. Therefore the results are different.
  From "comp.lang.c FAQ":

  If well-defined overflow characteristics are 
  important and negative values are not, or if you want 
  to steer clear of sign-extension problems when 
  manipulating bits or bytes, use one of the 
  corresponding unsigned types. (Beware when mixing 
  signed and unsigned values in expressions, though.)
  Although character types (especially unsigned char) 
  can be used as "tiny" integers, doing so is sometimes 
  more trouble than it's worth, due to unpredictable 
  sign extension and increased code size.

 Use unsigned when it is known in advance that the 
  value is not going to be negative. This helps 
  especially if you are doing division or 
  multiplication, bit-shifting or are using an array index.

 NEVER jump into a LOOP.

 Declare the variables to be local whenever possible, 
  especially loop control variables (induction).

 Since the compiler does not always do implicit 
  integral promotion, the programmer should do an 
  explicit cast when integral promotion is required.

 Reducing the size of division, multiplication & 
  modulus operations can reduce code size 
  substantially. Take the following code for example.

  foobar(unsigned int p1, unsigned char ch)
  {
      unsigned char ch1 = p1 % ch ;
      ....
  }

  For the modulus operation the variable ch will be 
  promoted to unsigned int first then the modulus 
  operation will be performed (this will lead to a call 
  to support routine _moduint()), and the result will 
  be casted to a char. If the code is changed to 

  foobar(unsigned int p1, unsigned char ch)
  {
      unsigned char ch1 = (unsigned char)p1 % ch ;
      ....
  }

  It would substantially reduce the code generated 
  (future versions of the compiler will be smart enough 
  to detect such optimization opportunities).

 Have a look at the assembly listing to get a "feeling" 
  for the code generation.

 Tools included in the distribution

+---------------+--------------------------------------+----------------------+
|     Name      |               Purpose                | Directory            |
+---------------+--------------------------------------+----------------------+
+---------------+--------------------------------------+----------------------+
|    uCsim      | Simulator for various architectures  | sdcc/sim/ucsim       |
+---------------+--------------------------------------+----------------------+
| keil2sdcc.pl  |       header file conversion         | sdcc/support/scripts |
+---------------+--------------------------------------+----------------------+
|    mh2h.c     |       header file conversion         | sdcc/support/scripts |
+---------------+--------------------------------------+----------------------+
|   as-gbz80    |              Assembler               | sdcc/bin             |
+---------------+--------------------------------------+----------------------+
|    as-z80     |              Assembler               | sdcc/bin             |
+---------------+--------------------------------------+----------------------+
|   asx8051     |              Assembler               | sdcc/bin             |
+---------------+--------------------------------------+----------------------+
|    sdcdb      |              Simulator               | sdcc/bin             |
+---------------+--------------------------------------+----------------------+
|    aslink     |               Linker                 | sdcc/bin             |
+---------------+--------------------------------------+----------------------+
|   link-z80    |               Linker                 | sdcc/bin             |
+---------------+--------------------------------------+----------------------+
|  link-gbz80   |               Linker                 | sdcc/bin             |
+---------------+--------------------------------------+----------------------+
|   packihx     |             ihx packer               | sdcc/bin             |
+---------------+--------------------------------------+----------------------+



 Documentation included in the distribution

+------------------------------------------------------+-------------------------------+
| Subject / Title                                      | Where to get / filename       |
+------------------------------------------------------+-------------------------------+
+------------------------------------------------------+-------------------------------+
| SDCC Compiler User Guide                             | You're reading it right now   |
+------------------------------------------------------+-------------------------------+
| Changelog of SDCC                                    | sdcc/Changelog                |
+------------------------------------------------------+-------------------------------+
| ASXXXX Assemblers and ASLINK Relocating Linker       | sdcc/as/doc/asxhtm.html       |
+------------------------------------------------------+-------------------------------+
| SDCC regression test                                 | sdcc/doc/test_suite_spec.pdf  |
+------------------------------------------------------+-------------------------------+
| Various notes                                        | sdcc/doc/*                    |
+------------------------------------------------------+-------------------------------+
| Notes on debugging with sdcdb                        | sdcc/debugger/README          |
+------------------------------------------------------+-------------------------------+
| Software simulator for microcontrollers              | sdcc/sim/ucsim/doc/index.html |
+------------------------------------------------------+-------------------------------+
| Temporary notes on the pic16 port                    | sdcc/src/pic16/NOTES          |
+------------------------------------------------------+-------------------------------+
| SDCC internal documentation (debugging file format)  | sdcc/doc/cdbfileformat.pdf    |
+------------------------------------------------------+-------------------------------+



 Related open source tools

+-----------+---------------------------------------------------------------+--------------------------------------------+
|   Name    | Purpose                                                       | Where to get                               |
+-----------+---------------------------------------------------------------+--------------------------------------------+
+-----------+---------------------------------------------------------------+--------------------------------------------+
|  gpsim    | PIC simulator                                                 | [http://www.dattalo.com/gnupic/gpsim.html] |
+-----------+---------------------------------------------------------------+--------------------------------------------+
| gputils   | GNU PIC utilities                                             | [http://sourceforge.net/projects/gputils]  |
+-----------+---------------------------------------------------------------+--------------------------------------------+
|   flP5    | PIC programmer                                                | [http://freshmeat.net/projects/flp5/]      |
+-----------+---------------------------------------------------------------+--------------------------------------------+
|  indent   | Formats C source - Master of the white spaces                 | [http://directory.fsf.org/GNU/indent.html] |
+-----------+---------------------------------------------------------------+--------------------------------------------+
| srecord   | Object file conversion, checksumming, ...                     | [http://sourceforge.net/projects/srecord]  |
+-----------+---------------------------------------------------------------+--------------------------------------------+
| objdump   | Object file conversion, ...                                   | Part of binutils (should be there anyway)  |
+-----------+---------------------------------------------------------------+--------------------------------------------+
| doxygen   | Source code documentation system                              | [http://www.doxygen.org]                   |
+-----------+---------------------------------------------------------------+--------------------------------------------+
| kdevelop  | IDE (has anyone tried integrating SDCC & sdcdb? Unix only)    | [http://www.kdevelop.org]                  |
+-----------+---------------------------------------------------------------+--------------------------------------------+
|  splint   | Statically checks c sources (see [lyx:more-pedantic-SPLINT])  | [http://www.splint.org]                    |
+-----------+---------------------------------------------------------------+--------------------------------------------+
|   ddd     | Debugger, serves nicely as GUI to sdcdb (Unix only)           | [http://www.gnu.org/software/ddd/]         |
+-----------+---------------------------------------------------------------+--------------------------------------------+



 Related documentation / recommended reading

+-----------------+----------------------------------------------+-------------------------------------------------------------+
|      Name       | Subject / Title                              |                        Where to get                         |
+-----------------+----------------------------------------------+-------------------------------------------------------------+
+-----------------+----------------------------------------------+-------------------------------------------------------------+
| c-refcard.pdf   | C Reference Card, 2 pages                    |         [http://refcards.com/refcards/c/index.html]         |
+-----------------+----------------------------------------------+-------------------------------------------------------------+
|     c-faq       | C-FAQ-list                                   |         [http://www.eskimo.com/~scs/C-faq/top.html]         |
+-----------------+----------------------------------------------+-------------------------------------------------------------+
|                 | Latest datasheet of the target CPU           |                           vendor                            |
+-----------------+----------------------------------------------+-------------------------------------------------------------+
|                 | Revision history of datasheet                |                           vendor                            |
+-----------------+----------------------------------------------+-------------------------------------------------------------+
| S. S. Muchnick  | Advanced Compiler Design and Implementation  | bookstore (very dedicated, probably read other books first) |
+-----------------+----------------------------------------------+-------------------------------------------------------------+



 Some Questions

Some questions answered, some pointers given - it might 
be time to in turn ask you some questions: 

 can you solve your project with the selected 
  microcontroller? Would you find out early or rather 
  late that your target is too small/slow/whatever? Can 
  you switch to a slightly better device if it doesn't fit?

 should you solve the problem with an 8 bit CPU? Or 
  would a 16/32 bit CPU and/or another programming 
  language be more adequate? Would an operating system 
  on the target device help?

 if you solved the problem, will the marketing 
  department be happy?

 if the marketing department is happy, will customers 
  be happy?

 if you're the project manager, marketing department 
  and maybe even the customer in one person, have you 
  tried to see the project from the outside?

 is the project done if you think it is done? Or is 
  just that other 
  interface/protocol/feature/configuration/option 
  missing? How about website, manual(s), 
  internationali(z|s)ation, packaging, labels, 2nd 
  source for components, electromagnetic 
  compatability/interference, documentation for 
  production, production test software, update 
  mechanism, patent issues?

 is your project adequately positioned in that magic 
  triangle: fame, fortune, fun?

Maybe not all answers to these questions are known and 
some answers may even be no, nevertheless knowing these 
questions may help you to avoid burnoutburnout is bad for electronic devices, programmers and 
motorcycle tyres
. Chances are you didn't want to hear some of them...

Support

SDCC has grown to be a large project. The compiler 
alone (without the preprocessor, assembler and linker) 
is well over 100,000 lines of code (blank stripped). 
The open source nature of this project is a key to its 
continued growth and support. You gain the benefit and 
support of many active software developers and end 
users. Is SDCC perfect? No, that's why we need your 
help. The developers take pride in fixing reported 
bugs. You can help by reporting the bugs and helping 
other SDCC users. There are lots of ways to contribute, 
and we encourage you to take part in making SDCC a 
great software package. 

The SDCC project is hosted on the SDCC sourceforge site 
at [http://sourceforge.net/projects/sdcc]. You'll find the complete set of mailing lists, 
forums, bug reporting system, patch submission system, download
 area and Subversion code repository there.

 Reporting Bugs

The recommended way of reporting bugs is using the 
infrastructure of the sourceforge site. You can follow 
the status of bug reports there and have an overview 
about the known bugs.

Bug reports are automatically forwarded to the 
developer mailing list and will be fixed ASAP. When 
reporting a bug, it is very useful to include a small 
test program (the smaller the better) which reproduces 
the problem. If you can isolate the problem by looking 
at the generated assembly code, this can be very 
helpful. Compiling your program with the --dumpall 
option can sometimes be useful in locating optimization 
problems. When reporting a bug please maker sure you:

 Attach the code you are compiling with SDCC. 

 Specify the exact command you use to run SDCC, or 
  attach your Makefile. 

 Specify the SDCC version (type "sdcc -v"), your 
  platform, and operating system. 

 Provide an exact copy of any error message or 
  incorrect output. 

 Put something meaningful in the subject of your message.

Please attempt to include these 5 important parts, as 
applicable, in all requests for support or when 
reporting any problems or bugs with SDCC. Though this 
will make your message lengthy, it will greatly improve 
your chance that SDCC users and developers will be able 
to help you. Some SDCC developers are frustrated by bug 
reports without code provided that they can use to 
reproduce and ultimately fix the problem, so please be 
sure to provide sample code if you are reporting a bug! 

Please have a short check that you are using a recent 
version of SDCC and the bug is not yet known. This is 
the link for reporting bugs: [http://sourceforge.net/tracker/?group_id=599&atid=100599].

 Requesting Features<sub:Requesting-Features>

Like bug reports feature requests are forwarded to the 
developer mailing list. This is the link for requesting 
features: [http://sourceforge.net/tracker/?group_id=599&atid=350599].

 Submitting patches

Like bug reports contributed patches are forwarded to 
the developer mailing list. This is the link for 
submitting patches: [http://sourceforge.net/tracker/?group_id=599&atid=300599].

You need to specify some parameters to the diff command 
for the patches to be useful. If you modified more than 
one file a patch created f.e. with "diff -Naur 
unmodified_directory modified_directory >my_changes.patch"
 will be fine, otherwise "diff -u sourcefile.c.orig 
sourcefile.c >my_changes.patch" will do.

 Getting Help

These links should take you directly to the [http://sourceforge.net/mail/?group_id=599||Mailing lists]Traffic on sdcc-devel and sdcc-user is about 100 
mails/month each not counting automated messages (mid 2003)
 and the [http://sourceforge.net/forum/?group_id=599||Forums], lists and forums are archived and searchable 
so if you are lucky someone already had a similar 
problem. While mails to the lists themselves are 
delivered promptly their web front end on sourceforge 
sometimes shows a severe time lag (up to several 
weeks), if you're seriously using SDCC please consider 
subscribing to the lists.

 ChangeLog

You can follow the status of the Subversion version of 
SDCC by watching the Changelog in the Subversion repository
[http://svn.sourceforge.net/viewcvs.cgi/*checkout*/sdcc/trunk/sdcc/ChangeLog].

 Release policy

Historically there often were long delays between 
official releases and the sourceforge download area 
tends to get not updated at all. Excuses in the past 
might have referred to problems with live range 
analysis, but as this was fixed a while ago, the 
current problem is that another excuse has to be found. 
Kidding aside, we have to get better there! On the 
other hand there are daily snapshots available at [http://sdcc.sourceforge.net/snap.php||snap], and 
you can always build the very last version (hopefully 
with many bugs fixed, and features added) from the 
source code available at [http://sdcc.sourceforge.net/snap.php#Source||Source].

 Examples

You'll find some small examples in the directory 
sdcc/device/examples/. More examples and libraries are 
available at The SDCC Open Knowledge Resource [http://sdccokr.dl9sec.de/] web site 
or at [http://www.pjrc.com/tech/8051/].

I did insert a reference to Paul's web site here 
although it seems rather dedicated to a specific 8032 
board (I think it's okay because it f.e. shows 
LCD/Harddisc interface and has a free 8051 monitor. 
Independent 8032 board vendors face hard competition of 
heavily subsidized development boards anyway).

Maybe we should include some links to real world 
applications. Preferably pointer to pointers (one for 
each architecture) so this stays manageable here?

 Quality control

The compiler is passed through nightly compile and 
build checks. The so called regression tests check that 
SDCC itself compiles flawlessly on several platforms 
and checks the quality of the code generated by SDCC by 
running the code through simulators. There is a 
separate document test_suite.pdf about this.

You'll find the test code in the directory 
sdcc/support/regression. You can run these tests 
manually by running make in this directory (or f.e. "
make test-mcs51" if you don't want to run the complete 
tests). The test code might also be interesting if you 
want to look for examples checking corner cases of SDCC 
or if you plan to submit patches.

The pic port uses a different set of regression tests, 
you'll find them in the directory sdcc/src/regression.

 Use of SDCC in Education

In short: highly encouragedthe phrase "use in education" might evoke the 
association "only fit for use in education". This 
connotation is not intended but nevertheless risked as 
the licensing of SDCC makes it difficult to offer 
educational discounts
. If your rationales are to:

 give students a chance to understand the complete 
  steps of code generation

 have a curriculum that can be extended for years. Then 
  you could use an fpga board as target and your 
  curriculum will seamlessly extend from logic 
  synthesis ([opencores.org||http://www.opencores.org], [http://www.oregano.at/ip/ip01.htm||Oregano]), over assembly programming, to C to 
  FPGA compilers ([http://sf.net/projects/fpgac||FPGAC]) and to C.

 be able to insert excursions about skills like using a 
  revision control system, submitting/applying patches, 
  using a type-setting (as opposed to word-processing) 
  engine LyX/LaTeX, using [http://www.sf.net||SourceForge], following some [http://en.wikipedia.org/wiki/Netiquette||netiquette], 
  understanding BSD/LGPL/GPL/Proprietary licensing, 
  growth models of Open Source Software, CPU 
  simulation, compiler regression tests. 
  And if there should be a shortage of ideas then you 
  can always point students to the ever-growing feature 
  request list [http://sourceforge.net/tracker/?group_id=599&atid=350599].

 not tie students to a specific host platform and 
  instead allow them to use a host platform of their 
  choice (among them Alpha, i386, i386_64, MacOs, Mips, 
  Sparc, Windows and eventually [http://wiki.laptop.org/wiki/One_Laptop_per_Child||OLPC])

 not encourage students to use illegal copies of 
  educational software

 be immune to licensing/availability/price changes of 
  the chosen tool chain

 be able to change to a new target platform without 
  having to adopt a new tool chain

 have complete control over and insight into the tool chain

 make your students aware about the pros and cons of 
  open source software development

 give back to the public as you are probably at least 
  partially publically funded

 give students a chance to publically prove their 
  skills and to possibly see a world wide impact

then SDCC is probably among the first choices. Well, 
probably SDCC might be the only choice.

SDCC Technical Data

 Optimizations

SDCC performs a host of standard optimizations in 
addition to some MCU specific optimizations. 

 Sub-expression Elimination

The compiler does local and global common subexpression 
elimination, e.g.: 

i = x + y + 1; 
j = x + y;

will be translated to

iTemp = x + y; 
i = iTemp + 1; 
j = iTemp;

Some subexpressions are not as obvious as the above 
example, e.g.:

a->b[i].c = 10; 
a->b[i].d = 11;

In this case the address arithmetic a->b[i] will be 
computed only once; the equivalent code in C would be.

iTemp = a->b[i]; 
iTemp.c = 10; 
iTemp.d = 11;

The compiler will try to keep these temporary variables 
in registers.

 Dead-Code Elimination

int global;

void f () { 
  int i; 
  i = 1;      /* dead store */ 
  global = 1; /* dead store */ 
  global = 2; 
  return; 
  global = 3; /* unreachable */ 
}

will be changed to

int global;

void f () {
  global = 2; 
}

 Copy-Propagation

int f() { 
  int i, j; 
  i = 10; 
  j = i; 
  return j; 
}

will be changed to 

int f() { 
  int i, j; 
  i = 10; 
  j = 10; 
  return 10; 
}

Note: the dead stores created by this copy propagation 
will be eliminated by dead-code elimination.

 Loop Optimizations<sub:Loop-Optimizations>

Two types of loop optimizations are done by SDCC loop 
invariant lifting and strength reduction of loop 
induction variables. In addition to the strength 
reduction the optimizer marks the induction variables 
and the register allocator tries to keep the induction 
variables in registers for the duration of the loop. 
Because of this preference of the register allocator, 
loop induction optimization causes an increase in 
register pressure, which may cause unwanted spilling of 
other temporary variables into the stack / data space. 
The compiler will generate a warning message when it is 
forced to allocate extra space either on the stack or 
data space. If this extra space allocation is 
undesirable then induction optimization can be 
eliminated either for the entire source file (with -
-noinduction option) or for a given function only using #pragma 
noinduction.

Loop Invariant:

for (i = 0 ; i < 100 ; i ++) 
    f += k + l;

changed to

itemp = k + l; 
for (i = 0; i < 100; i++) 
    f += itemp;

As mentioned previously some loop invariants are not as 
apparent, all static address computations are also 
moved out of the loop.

Strength Reduction, this optimization substitutes an 
expression by a cheaper expression:

for (i=0;i < 100; i++)
    ar[i*5] = i*3;

changed to

itemp1 = 0; 
itemp2 = 0; 
for (i=0;i< 100;i++) { 
    ar[itemp1] = itemp2; 
    itemp1 += 5; 
    itemp2 += 3; 
}

The more expensive multiplication is changed to a less 
expensive addition.

 Loop Reversing

This optimization is done to reduce the overhead of 
checking loop boundaries for every iteration. Some 
simple loops can be reversed and implemented using a "
decrement and jump if not zero" instruction. SDCC checks 
for the following criterion to determine if a loop is 
reversible (note: more sophisticated compilers use 
data-dependency analysis to make this determination, 
SDCC uses a more simple minded analysis).

 The 'for' loop is of the form 
  
  for(<symbol> = <expression>; <sym> [< | <=] 
  <expression>; [<sym>++ | <sym> += 1])
      <for body>

 The <for body> does not contain "continue" or 'break".

 All goto's are contained within the loop.

 No function calls within the loop.

 The loop control variable <sym> is not assigned any 
  value within the loop

 The loop control variable does NOT participate in any 
  arithmetic operation within the loop.

 There are NO switch statements in the loop.

 Algebraic Simplifications

SDCC does numerous algebraic simplifications, the 
following is a small sub-set of these optimizations.

i = j + 0;     /* changed to: */     i = j; 
i /= 2;        /* changed to: */     i >>= 1; 
i = j - j;     /* changed to: */     i = 0; 
i = j / 1;     /* changed to: */     i = j;

Note the subexpressions given above are generally 
introduced by macro expansions or as a result of 
copy/constant propagation.

 'switch' Statements<sub:'switch'-Statements>

SDCC can optimize switch statements to jump tables. It 
makes the decision based on an estimate of the 
generated code size. SDCC is quite liberal in the 
requirements for jump table generation: 

 The labels need not be in order, and the starting 
  number need not be one or zero, the case labels are 
  in numerical sequence or not too many case labels are missing.

  switch(i) {                          switch (i) { 
     case 4: ...                          case 0: ... 
     case 5: ...                          case 1: ... 
     case 3: ...                          
     case 6: ...                          case 3: ... 
     case 7: ...                          case 4: ... 
     case 8: ...                          case 5: ... 
     case 9: ...                          case 6: ... 
     case 10: ...                         case 7: ... 
     case 11: ...                         case 8: ... 
  }                                    }

  Both the above switch statements will be implemented 
  using a jump-table. The example to the right side is 
  slightly more efficient as the check for the lower 
  boundary of the jump-table is not needed.

 The number of case labels is not larger than supported 
  by the target architecture.

 If the case labels are not in numerical sequence 
  ('gaps' between cases) SDCC checks whether a jump 
  table with additionally inserted dummy cases is still 
  attractive. 

 If the starting number is not zero and a check for the 
  lower boundary of the jump-table can thus be 
  eliminated SDCC might insert dummy cases 0, ... .

Switch statements which have large gaps in the numeric 
sequence or those that have too many case labels can be 
split into more than one switch statement for efficient 
code generation, e.g.:

switch (i) { 
  case 1: ... 
  case 2: ... 
  case 3: ... 
  case 4: ... 
  case 5: ... 
  case 6: ... 
  case 7: ... 
  case 101: ... 
  case 102: ... 
  case 103: ... 
  case 104: ... 
  case 105: ... 
  case 106: ... 
  case 107: ... 
}

If the above switch statement is broken down into two 
switch statements

switch (i) { 
  case 1: ... 
  case 2: ... 
  case 3: ... 
  case 4: ... 
  case 5: ... 
  case 6: ... 
  case 7: ... 
}

and

switch (i) { 
  case 101: ... 
  case 102: ... 
  case 103: ... 
  case 104: ... 
  case 105: ... 
  case 106: ... 
  case 107: ... 
}

then both the switch statements will be implemented 
using jump-tables whereas the unmodified switch 
statement will not be.

There might be reasons which SDCC cannot know about to 
either favour or not favour jump tables. If the target 
system has to be as quick for the last switch case as 
for the first (pro jump table), or if the switch 
argument is known to be zero in the majority of the 
cases (contra jump table).

The pragma nojtbound can be used to turn off checking 
the jump table boundaries. It has no effect if a 
default label is supplied. Use of this pragma is 
dangerous: if the switch argument is not matched by a 
case statement the processor will happily jump into Nirvana.

 Bit-shifting Operations.

Bit shifting is one of the most frequently used 
operation in embedded programming. SDCC tries to 
implement bit-shift operations in the most efficient 
way possible, e.g.:

unsigned char i;
... 
i >>= 4; 
...

generates the following code:

mov  a,_i 
swap a 
anl  a,#0x0f 
mov  _i,a

In general SDCC will never setup a loop if the shift 
count is known. Another example:

unsigned int i; 
... 
i >>= 9; 
...

will generate:

mov  a,(_i + 1) 
mov  (_i + 1),#0x00 
clr  c 
rrc  a 
mov  _i,a

 Bit-rotation

A special case of the bit-shift operation is bit rotation
, SDCC recognizes the following expression to be a left 
bit-rotation:

unsigned  char i;           /* unsigned is needed for rotation */ 
... 
i = ((i << 1) | (i >> 7)); 
...

will generate the following code:

mov  a,_i 
rl   a 
mov  _i,a

SDCC uses pattern matching on the parse tree to 
determine this operation.Variations of this case will 
also be recognized as bit-rotation, i.e.: 

i = ((i >> 7) | (i << 1)); /* left-bit rotation */

 Nibble and Byte Swapping

Other special cases of the bit-shift operations are 
nibble or byte swapping, SDCC recognizes the following 
expressions:

unsigned  char i; 
unsigned  int j; 
... 
i = ((i << 4) | (i >> 4)); 
j = ((j << 8) | (j >> 8)); 

and generates a swap instruction for the nibble swapping
 or move instructions for the byte swapping. The "j" 
example can be used to convert from little to 
big-endian or vice versa. If you want to change the 
endianness of a signed integer you have to cast to 
(unsigned int) first.

Note that SDCC stores numbers in little-endianUsually 8-bit processors don't care much about 
endianness. This is not the case for the standard 8051 
which only has an instruction to increment its dptr
-datapointer so little-endian is the more efficient 
byte order.
 format (i.e. lowest order first).

 Highest Order Bit / Any Order Bit

It is frequently required to obtain the highest order 
bit of an integral type (long, int, short or char 
types). Also obtaining any other order bit is not 
uncommon. SDCC recognizes the following expressions to 
yield the highest order bit and generates optimized 
code for it, e.g.:

unsigned int gint; 

foo () { 
  unsigned char hob1, aob1; 
  bit hob2, hob3, aob2, aob3; 
  ... 
  hob1 = (gint >> 15) & 1; 
  hob2 = (gint >> 15) & 1; 
  hob3 = gint & 0x8000; 
  aob1 = (gint >> 9) & 1; 
  aob2 = (gint >> 8) & 1; 
  aob3 = gint & 0x0800; 
  .. 
}

will generate the following code:

                          61 ;  hob.c 7 
000A E5*01                62         mov   a,(_gint + 1) 
000C 23                   63         rl    a 
000D 54 01                64         anl   a,#0x01 
000F F5*02                65         mov   _foo_hob1_1_1,a 
                          66 ;  hob.c 8 
0011 E5*01                67         mov   a,(_gint + 1) 
0013 33                   68         rlc   a 
0014 92*00                69         mov   _foo_hob2_1_1,c 
                          66 ;  hob.c 9 
0016 E5*01                67         mov   a,(_gint + 1) 
0018 33                   68         rlc   a 
0019 92*01                69         mov   _foo_hob3_1_1,c 
                          70 ;  hob.c 10 
001B E5*01                71         mov   a,(_gint + 1) 
001D 03                   72         rr    a 
001E 54 01                73         anl   a,#0x01 
0020 F5*03                74         mov   _foo_aob1_1_1,a 
                          75 ;  hob.c 11 
0022 E5*01                76         mov   a,(_gint + 1) 
0024 13                   77         rrc   a 
0025 92*02                78         mov   _foo_aob2_1_1,c 
                          79 ;  hob.c 12 
0027 E5*01                80         mov   a,(_gint + 1) 
0029 A2 E3                81         mov   c,acc[3] 
002B 92*03                82         mov   _foo_aob3_1_1,c 

Other variations of these cases however will not be 
recognized. They are standard C expressions, so I 
heartily recommend these be the only way to get the 
highest order bit, (it is portable). Of course it will 
be recognized even if it is embedded in other 
expressions, e.g.:

xyz = gint + ((gint >> 15) & 1);

will still be recognized.

 Higher Order Byte / Higher Order Word

It is also frequently required to obtain a higher order 
byte or word of a larger integral type (long, int or 
short types). SDCC recognizes the following expressions 
to yield the higher order byte or word and generates 
optimized code for it, e.g.:

unsigned int gint; 
unsigned long int glong; 

foo () { 
  unsigned char hob1, hob2; 
  unsigned int how1, how2; 
  ... 
  hob1 = (gint >> 8) & 0xFF; 
  hob2 = glong >> 24; 
  how1 = (glong >> 16) & 0xFFFF; 
  how2 = glong >> 8; 
  .. 
}

will generate the following code:

                          91 ;  hob.c 15 
0037 85*01*06             92         mov   _foo_hob1_1_1,(_gint + 1) 
                          93 ;  hob.c 16 
003A 85*05*07             94         mov   _foo_hob2_1_1,(_glong + 3) 
                          95 ;  hob.c 17 
003D 85*04*08             96         mov   _foo_how1_1_1,(_glong + 2) 
0040 85*05*09             97         mov   (_foo_how1_1_1 + 1),(_glong + 3) 
0043 85*03*0A             98         mov   _foo_how2_1_1,(_glong + 1) 
0046 85*04*0B             99         mov   (_foo_how2_1_1 + 1),(_glong + 2) 

Again, variations of these cases may not be recognized. 
They are standard C expressions, so I heartily 
recommend these be the only way to get the higher order 
byte/word, (it is portable). Of course it will be 
recognized even if it is embedded in other expressions, e.g.:

xyz = gint + ((gint >> 8) & 0xFF);

will still be recognized.

 Peephole Optimizer<sub:Peephole-Optimizer>

The compiler uses a rule based, pattern matching and 
re-writing mechanism for peep-hole optimization. It is 
inspired by copt a peep-hole optimizer by Christopher 
W. Fraser (cwfraser @ microsoft.com). A default set of 
rules are compiled into the compiler, additional rules 
may be added with the --peep-file <filename> option. 
The rule language is best illustrated with examples.

replace { 
  mov %1,a 
  mov a,%1
} by {
  mov %1,a
}

The above rule will change the following assembly sequence:

mov r1,a 
mov a,r1

to

mov r1,a

Note: All occurrences of a %n (pattern variable) must 
denote the same string. With the above rule, the 
assembly sequence:

mov r1,a 
mov a,r2

will remain unmodified.

Other special case optimizations may be added by the 
user (via --peep-file option). E.g. some variants of 
the 8051 MCU allow only ajmp and acall. The following 
two rules will change all ljmp and lcall to ajmp and acall

replace { lcall %1 } by { acall %1 } 
replace { ljmp %1 } by { ajmp %1 }

The inline-assembler code is also passed through the 
peep hole optimizer, thus the peephole optimizer can 
also be used as an assembly level macro expander. The 
rules themselves are MCU dependent whereas the rule 
language infra-structure is MCU independent. Peephole 
optimization rules for other MCU can be easily 
programmed using the rule language.

The syntax for a rule is as follows:

rule := replace [ restart ] '{' <assembly sequence> 
'\n' 
                            '}' by '{' '\n' 
                                <assembly sequence> '\n' 
                            '}' [if <functionName> ] '\n' 

<assembly sequence> := assembly instruction (each 
instruction including labels must be on a separate line).

The optimizer will apply to the rules one by one from 
the top in the sequence of their appearance, it will 
terminate when all rules are exhausted. If the 
'restart' option is specified, then the optimizer will 
start matching the rules again from the top, this 
option for a rule is expensive (performance), it is 
intended to be used in situations where a 
transformation will trigger the same rule again. An 
example of this (not a good one, it has side effects) 
is the following rule:

replace restart { 
  pop %1 
  push %1 } by { 
  ; nop 
}

Note that the replace pattern cannot be a blank, but 
can be a comment line. Without the 'restart' option 
only the innermost 'pop' 'push' pair would be 
eliminated, i.e.:

pop ar1 
pop ar2 
push ar2 
push ar1

would result in:

pop ar1 
; nop 
push ar1

with the restart option the rule will be applied again 
to the resulting code and then all the pop-push pairs 
will be eliminated to yield:

; nop 
; nop

A conditional function can be attached to a rule. 
Attaching rules are somewhat more involved, let me 
illustrate this with an example.

replace { 
     ljmp %5 
%2:
} by { 
     sjmp %5 
%2:
} if labelInRange

The optimizer does a look-up of a function name table 
defined in function callFuncByName in the source file 
SDCCpeeph.c, with the name labelInRange. If it finds a 
corresponding entry the function is called. Note there 
can be no parameters specified for these functions, in 
this case the use of %5 is crucial, since the function 
labelInRange expects to find the label in that 
particular variable (the hash table containing the 
variable bindings is passed as a parameter). If you 
want to code more such functions, take a close look at 
the function labelInRange and the calling mechanism in 
source file SDCCpeeph.c. Currently implemented are 
labelInRange, labelRefCount, labelIsReturnOnly, 
operandsNotSame, xramMovcOption, 24bitMode, 
portIsDS390, 24bitModeAndPortDS390 and notVolatile.

I know this whole thing is a little kludgey, but maybe 
some day we will have some better means. If you are 
looking at this file, you will see the default rules 
that are compiled into the compiler, you can add your 
own rules in the default set there if you get tired of 
specifying the --peep-file option.

 ANSI-Compliance<sub:ANSI-Compliance>

Deviations from the compliance:

 functions are not reentrant unless explicitly declared 
  as such or the --stack-auto command line option is specified.

 structures and unions cannot be assigned values 
  directly, cannot be passed as function parameters or 
  assigned to each other and cannot be a return value 
  from a function, e.g.:

  struct s { ... }; 
  struct s s1, s2; 
  foo() 
  { 
      ... 
      s1 = s2 ; /* is invalid in SDCC although allowed in 
  ANSI */ 
      ... 
  }
  struct s foo1 (struct s parms) /* invalid in SDCC 
  although allowed in ANSI */
  { 
      struct s rets; 
      ... 
      return rets;/* is invalid in SDCC although allowed in 
  ANSI */ 
  }

 initialization of structure arrays must be fully braced.

  struct s { char x } a[] = {1, 2}; /* invalid in SDCC */
  struct s { char x } a[] = {{1}, {2}}; /* OK */

 'long long' (64 bit integers) not supported.

 'double' precision floating point not supported.

 Old K&R style function declarations are NOT allowed.

  foo(i,j) /* this old style of function declarations 
  */ 
  int i,j; /* are valid in ANSI but not valid in SDCC 
  */ 
  { 
      ... 
  }

 Most enhancements in C99 are not supported, f.e.:

  inline int increment (int a) { return a+1; } /* is 
  invalid in SDCC although allowed in C99 */
  for (int i=0; i<10; i++) /* is invalid in SDCC 
  although allowed in C99 */

 Certain words that are valid identifiers in the 
  standard may be reserved words in SDCC unless the --std-c89
   or --std-c99 command line options are used. These 
  may include (depending on the selected processor): 
  'at', 'banked', 'bit', 'code', 'critical', 'data', 
  'eeprom', 'far', 'flash', 'idata', 'interrupt', 
  'near', 'nonbanked', 'pdata', 'reentrant', 'sbit', 
  'sfr', 'shadowregs', 'sram', 'using', 'wparam', 
  'xdata', '_overlay', '_asm', '_endasm', and '_naked'. 
  Compliant equivalents of these keywords are always 
  available in a form that begin with two underscores, 
  f.e. '__data' instead of 'data'.

 Cyclomatic Complexity

Cyclomatic complexity of a function is defined as the 
number of independent paths the program can take during 
execution of the function. This is an important number 
since it defines the number test cases you have to 
generate to validate the function. The accepted 
industry standard for complexity number is 10, if the 
cyclomatic complexity reported by SDCC exceeds 10 you 
should think about simplification of the function 
logic. Note that the complexity level is not related to 
the number of lines of code in a function. Large 
functions can have low complexity, and small functions 
can have large complexity levels. 

SDCC uses the following formula to compute the complexity:


complexity = (number of edges in control flow graph) - 
(number of nodes in control flow graph) + 2;

Having said that the industry standard is 10, you 
should be aware that in some cases it be may 
unavoidable to have a complexity level of less than 10. 
For example if you have switch statement with more than 
10 case labels, each case label adds one to the 
complexity level. The complexity level is by no means 
an absolute measure of the algorithmic complexity of 
the function, it does however provide a good starting 
point for which functions you might look at for further 
optimization.

 Retargetting for other Processors

The issues for retargetting the compiler are far too 
numerous to be covered by this document. What follows 
is a brief description of each of the seven phases of 
the compiler and its MCU dependency.

 Parsing the source and building the annotated parse 
  tree. This phase is largely MCU independent (except 
  for the language extensions). Syntax & semantic 
  checks are also done in this phase, along with some 
  initial optimizations like back patching labels and 
  the pattern matching optimizations like bit-rotation etc.

 The second phase involves generating an intermediate 
  code which can be easy manipulated during the later 
  phases. This phase is entirely MCU independent. The 
  intermediate code generation assumes the target 
  machine has unlimited number of registers, and 
  designates them with the name iTemp. The compiler can 
  be made to dump a human readable form of the code 
  generated by using the --dumpraw option.

 This phase does the bulk of the standard optimizations 
  and is also MCU independent. This phase can be broken 
  down into several sub-phases:
  
  Break down intermediate code (iCode) into basic blocks.
  Do control flow & data flow analysis on the basic blocks.
  Do local common subexpression elimination, then 
  global subexpression elimination
  Dead code elimination
  Loop optimizations
  If loop optimizations caused any changes then do 
  'global subexpression elimination' and 'dead code 
  elimination' again.

 This phase determines the live-ranges; by live range I 
  mean those iTemp variables defined by the compiler 
  that still survive after all the optimizations. Live 
  range analysis is essential for register allocation, 
  since these computation determines which of these 
  iTemps will be assigned to registers, and for how long.

 Phase five is register allocation. There are two parts 
  to this process.
  
  The first part I call 'register packing' (for lack of 
  a better term). In this case several MCU specific 
  expression folding is done to reduce register pressure.
  
  The second part is more MCU independent and deals 
  with allocating registers to the remaining live 
  ranges. A lot of MCU specific code does creep into 
  this phase because of the limited number of index 
  registers available in the 8051.

 The Code generation phase is (unhappily), entirely MCU 
  dependent and very little (if any at all) of this 
  code can be reused for other MCU. However the scheme 
  for allocating a homogenized assembler operand for 
  each iCode operand may be reused.

 As mentioned in the optimization section the peep-hole 
  optimizer is rule based system, which can 
  reprogrammed for other MCUs.

Compiler internals

 The anatomy of the compiler<sub:The-anatomy-of>

This is an excerpt from an article published in Circuit 
Cellar Magazine in August 2000. It's a little outdated 
(the compiler is much more efficient now and 
user/developer friendly), but pretty well exposes the 
guts of it all.

The current version of SDCC can generate code for Intel 
8051 and Z80 MCU. It is fairly easy to retarget for 
other 8-bit MCU. Here we take a look at some of the 
internals of the compiler. 

  Parsing 

Parsing the input source file and creating an AST 
(Annotated Syntax Tree). This phase also involves 
propagating types (annotating each node of the parse 
tree with type information) and semantic analysis. 
There are some MCU specific parsing rules. For example 
the storage classes, the extended storage classes are 
MCU specific while there may be a xdata storage class 
for 8051 there is no such storage class for z80 or 
Atmel AVR. SDCC allows MCU specific storage class 
extensions, i.e. xdata will be treated as a storage 
class specifier when parsing 8051 C code but will be 
treated as a C identifier when parsing z80 or ATMEL AVR 
C code.

  Generating iCode

Intermediate code generation. In this phase the AST is 
broken down into three-operand form (iCode). These 
three operand forms are represented as doubly linked 
lists. ICode is the term given to the intermediate form 
generated by the compiler. ICode example section shows 
some examples of iCode generated for some simple C 
source functions.

  Optimizations.

Bulk of the target independent optimizations is 
performed in this phase. The optimizations include 
constant propagation, common sub-expression 
elimination, loop invariant code movement, strength 
reduction of loop induction variables and dead-code elimination.

  Live range analysis

During intermediate code generation phase, the compiler 
assumes the target machine has infinite number of 
registers and generates a lot of temporary variables. 
The live range computation determines the lifetime of 
each of these compiler-generated temporaries. A picture 
speaks a thousand words. ICode example sections show 
the live range annotations for each of the operand. It 
is important to note here, each iCode is assigned a 
number in the order of its execution in the function. 
The live ranges are computed in terms of these numbers. 
The from number is the number of the iCode which first 
defines the operand and the to number signifies the 
iCode which uses this operand last.

  Register Allocation

The register allocation determines the type and number 
of registers needed by each operand. In most MCUs only 
a few registers can be used for indirect addressing. In 
case of 8051 for example the registers R0 & R1 can be 
used to indirectly address the internal ram and DPTR to 
indirectly address the external ram. The compiler will 
try to allocate the appropriate register to pointer 
variables if it can. ICode example section shows the 
operands annotated with the registers assigned to them. 
The compiler will try to keep operands in registers as 
much as possible; there are several schemes the 
compiler uses to do achieve this. When the compiler 
runs out of registers the compiler will check to see if 
there are any live operands which is not used or 
defined in the current basic block being processed, if 
there are any found then it will push that operand and 
use the registers in this block, the operand will then 
be popped at the end of the basic block. 

There are other MCU specific considerations in this 
phase. Some MCUs have an accumulator; very short-lived 
operands could be assigned to the accumulator instead 
of a general-purpose register.

  Code generation

Figure II gives a table of iCode operations supported 
by the compiler. The code generation involves 
translating these operations into corresponding 
assembly code for the processor. This sounds overly 
simple but that is the essence of code generation. Some 
of the iCode operations are generated on a MCU specific 
manner for example, the z80 port does not use registers 
to pass parameters so the SEND and RECV iCode 
operations will not be generated, and it also does not 
support JUMPTABLES. 
<Where is Figure II?>

In the original article Figure II was announced to be 
downloadable on Circuit Cellar's web site. 
Unfortunately it never seemed to have shown up there, 
so: where is Figure II?

  ICode Example

This section shows some details of iCode. The example C 
code does not do anything useful; it is used as an 
example to illustrate the intermediate code generated 
by the compiler.

1. xdata int * p;
2. int gint;
3. /* This function does nothing useful. It is used
4.    for the purpose of explaining iCode */
5. short function (data int *x)
6. {
7.   short i=10;   /* dead initialization eliminated */
8.   short sum=10; /* dead initialization eliminated */
9.   short mul;
10.  int j ;
11.  while (*x) *x++ = *p++; 
12.    sum = 0 ; 
13.  mul = 0;
14.  /* compiler detects i,j to be induction variables */
15.  for (i = 0, j = 10 ; i < 10 ; i++, j--) {
16.    sum += i;
17.    mul += i * 3;   /* this multiplication remains */
18.    gint += j * 3;  /* this multiplication changed to 
addition */
19.  }
20.  return sum+mul;
21. }

In addition to the operands each iCode contains 
information about the filename and line it corresponds 
to in the source file. The first field in the listing 
should be interpreted as follows:
Filename(linenumber: iCode Execution sequence number : 
ICode hash table key : loop depth of the iCode).
Then follows the human readable form of the ICode 
operation. Each operand of this triplet form can be of 
three basic types a) compiler generated temporary b) 
user defined variable c) a constant value. Note that 
local variables and parameters are replaced by compiler 
generated temporaries. Live ranges are computed only 
for temporaries (i.e. live ranges are not computed for 
global variables). Registers are allocated for 
temporaries only. Operands are formatted in the 
following manner:
Operand Name [lr live-from : live-to ] { type 
information } [ registers allocated ].
As mentioned earlier the live ranges are computed in 
terms of the execution sequence number of the iCodes, 
for example 
the iTemp0 is live from (i.e. first defined in iCode 
with execution sequence number 3, and is last used in 
the iCode with sequence number 5). For induction 
variables such as iTemp21 the live range computation 
extends the lifetime from the start to the end of the loop.
The register allocator used the live range information 
to allocate registers, the same registers may be used 
for different temporaries if their live ranges do not 
overlap, for example r0 is allocated to both iTemp6 and 
to iTemp17 since their live ranges do not overlap. In 
addition the allocator also takes into consideration 
the type and usage of a temporary, for example itemp6 
is a pointer to near space and is used as to fetch data 
from (i.e. used in GET_VALUE_AT_ADDRESS) so it is 
allocated a pointer register (r0). Some short lived 
temporaries are allocated to special registers which 
have meaning to the code generator e.g. iTemp13 is 
allocated to a pseudo register CC which tells the back 
end that the temporary is used only for a conditional 
jump the code generation makes use of this information 
to optimize a compare and jump ICode.
There are several loop optimizations performed by the 
compiler. It can detect induction variables iTemp21(i) 
and iTemp23(j). Also note the compiler does selective 
strength reduction, i.e. the multiplication of an 
induction variable in line 18 (gint = j * 3) is changed 
to addition, a new temporary iTemp17 is allocated and 
assigned a initial value, a constant 3 is then added 
for each iteration of the loop. The compiler does not 
change the multiplication in line 17 however since the 
processor does support an 8 * 8 bit multiplication.
Note the dead code elimination optimization eliminated 
the dead assignments in line 7 & 8 to I and sum respectively.


Sample.c (5:1:0:0) _entry($9) :

Sample.c(5:2:1:0) proc _function [lr0:0]{function short}

Sample.c(11:3:2:0) iTemp0 [lr3:5]{_near * int}[r2] = 
recv 

Sample.c(11:4:53:0) preHeaderLbl0($11) :

Sample.c(11:5:55:0) iTemp6 [lr5:16]{_near * int}[r0] := 
iTemp0 [lr3:5]{_near * int}[r2]

Sample.c(11:6:5:1) _whilecontinue_0($1) :

Sample.c(11:7:7:1) iTemp4 [lr7:8]{int}[r2 r3] = 
@[iTemp6 [lr5:16]{_near * int}[r0]]

Sample.c(11:8:8:1) if iTemp4 [lr7:8]{int}[r2 r3] == 0 
goto _whilebreak_0($3)

Sample.c(11:9:14:1) iTemp7 [lr9:13]{_far * int}[DPTR] 
:= _p [lr0:0]{_far * int}

Sample.c(11:10:15:1) _p [lr0:0]{_far * int} = _p 
[lr0:0]{_far * int} + 0x2 {short}

Sample.c(11:13:18:1) iTemp10 [lr13:14]{int}[r2 r3] = 
@[iTemp7 [lr9:13]{_far * int}[DPTR]]

Sample.c(11:14:19:1) *(iTemp6 [lr5:16]{_near * 
int}[r0]) := iTemp10 [lr13:14]{int}[r2 r3]

Sample.c(11:15:12:1) iTemp6 [lr5:16]{_near * int}[r0] = 
iTemp6 [lr5:16]{_near * int}[r0] + 0x2 {short}

Sample.c(11:16:20:1) goto _whilecontinue_0($1)

Sample.c(11:17:21:0)_whilebreak_0($3) :

Sample.c(12:18:22:0) iTemp2 [lr18:40]{short}[r2] := 0x0 {short}

Sample.c(13:19:23:0) iTemp11 [lr19:40]{short}[r3] := 
0x0 {short}

Sample.c(15:20:54:0)preHeaderLbl1($13) :

Sample.c(15:21:56:0) iTemp21 [lr21:38]{short}[r4] := 
0x0 {short}

Sample.c(15:22:57:0) iTemp23 [lr22:38]{int}[r5 r6] := 
0xa {int}

Sample.c(15:23:58:0) iTemp17 [lr23:38]{int}[r7 r0] := 
0x1e {int}

Sample.c(15:24:26:1)_forcond_0($4) :

Sample.c(15:25:27:1) iTemp13 [lr25:26]{char}[CC] = 
iTemp21 [lr21:38]{short}[r4] < 0xa {short}

Sample.c(15:26:28:1) if iTemp13 [lr25:26]{char}[CC] == 
0 goto _forbreak_0($7)

Sample.c(16:27:31:1) iTemp2 [lr18:40]{short}[r2] = 
iTemp2 [lr18:40]{short}[r2] + ITemp21 [lr21:38]{short}[r4]

Sample.c(17:29:33:1) iTemp15 [lr29:30]{short}[r1] = 
iTemp21 [lr21:38]{short}[r4] * 0x3 {short}

Sample.c(17:30:34:1) iTemp11 [lr19:40]{short}[r3] = 
iTemp11 [lr19:40]{short}[r3] + iTemp15 [lr29:30]{short}[r1]

Sample.c(18:32:36:1:1) iTemp17 [lr23:38]{int}[r7 r0]= 
iTemp17 [lr23:38]{int}[r7 r0]- 0x3 {short}

Sample.c(18:33:37:1) _gint [lr0:0]{int} = _gint 
[lr0:0]{int} + iTemp17 [lr23:38]{int}[r7 r0]

Sample.c(15:36:42:1) iTemp21 [lr21:38]{short}[r4] = 
iTemp21 [lr21:38]{short}[r4] + 0x1 {short}

Sample.c(15:37:45:1) iTemp23 [lr22:38]{int}[r5 r6]= 
iTemp23 [lr22:38]{int}[r5 r6]- 0x1 {short}

Sample.c(19:38:47:1) goto _forcond_0($4)

Sample.c(19:39:48:0)_forbreak_0($7) :

Sample.c(20:40:49:0) iTemp24 [lr40:41]{short}[DPTR] = 
iTemp2 [lr18:40]{short}[r2] + ITemp11 [lr19:40]{short}[r3]

Sample.c(20:41:50:0) ret iTemp24 [lr40:41]{short}

Sample.c(20:42:51:0)_return($8) :

Sample.c(20:43:52:0) eproc _function [lr0:0]{ ia0 re0 
rm0}{function short}

Finally the code generated for this function:


.area DSEG (DATA)

_p::

  .ds 2

_gint::

  .ds 2

; sample.c 5

; ----------------------------------------------

; function function

; ----------------------------------------------

_function:

; iTemp0 [lr3:5]{_near * int}[r2] = recv 

  mov r2,dpl

; iTemp6 [lr5:16]{_near * int}[r0] := iTemp0 
[lr3:5]{_near * int}[r2]

  mov ar0,r2

;_whilecontinue_0($1) :

00101$:

; iTemp4 [lr7:8]{int}[r2 r3] = @[iTemp6 [lr5:16]{_near 
* int}[r0]]

; if iTemp4 [lr7:8]{int}[r2 r3] == 0 goto _whilebreak_0($3)

  mov ar2,@r0

  inc r0

  mov ar3,@r0

  dec r0

  mov a,r2

  orl a,r3

  jz 00103$

00114$:

; iTemp7 [lr9:13]{_far * int}[DPTR] := _p [lr0:0]{_far 
* int}

  mov dpl,_p

  mov dph,(_p + 1)

; _p [lr0:0]{_far * int} = _p [lr0:0]{_far * int} + 0x2 {short}

  mov a,#0x02

  add a,_p

  mov _p,a

  clr a

  addc a,(_p + 1)

  mov (_p + 1),a

; iTemp10 [lr13:14]{int}[r2 r3] = @[iTemp7 
[lr9:13]{_far * int}[DPTR]]

  movx a,@dptr

  mov r2,a

  inc dptr

  movx a,@dptr

  mov r3,a

; *(iTemp6 [lr5:16]{_near * int}[r0]) := iTemp10 
[lr13:14]{int}[r2 r3]

  mov @r0,ar2

  inc r0

  mov @r0,ar3

; iTemp6 [lr5:16]{_near * int}[r0] = 

; iTemp6 [lr5:16]{_near * int}[r0] + 

; 0x2 {short}

  inc r0

; goto _whilecontinue_0($1)

  sjmp 00101$

; _whilebreak_0($3) :

00103$:

; iTemp2 [lr18:40]{short}[r2] := 0x0 {short}

  mov r2,#0x00

; iTemp11 [lr19:40]{short}[r3] := 0x0 {short}

  mov r3,#0x00

; iTemp21 [lr21:38]{short}[r4] := 0x0 {short}

  mov r4,#0x00

; iTemp23 [lr22:38]{int}[r5 r6] := 0xa {int}

  mov r5,#0x0A

  mov r6,#0x00

; iTemp17 [lr23:38]{int}[r7 r0] := 0x1e {int}

  mov r7,#0x1E

  mov r0,#0x00

; _forcond_0($4) :

00104$:

; iTemp13 [lr25:26]{char}[CC] = iTemp21 
[lr21:38]{short}[r4] < 0xa {short}

; if iTemp13 [lr25:26]{char}[CC] == 0 goto _forbreak_0($7)

  clr c

  mov a,r4

  xrl a,#0x80

  subb a,#0x8a

  jnc 00107$

00115$:

; iTemp2 [lr18:40]{short}[r2] = iTemp2 
[lr18:40]{short}[r2] + 

; iTemp21 [lr21:38]{short}[r4]

  mov a,r4

  add a,r2

  mov r2,a

; iTemp15 [lr29:30]{short}[r1] = iTemp21 
[lr21:38]{short}[r4] * 0x3 {short}

  mov b,#0x03

  mov a,r4

  mul ab

  mov r1,a

; iTemp11 [lr19:40]{short}[r3] = iTemp11 
[lr19:40]{short}[r3] + 

; iTemp15 [lr29:30]{short}[r1]

  add a,r3

  mov r3,a

; iTemp17 [lr23:38]{int}[r7 r0]= iTemp17 
[lr23:38]{int}[r7 r0]- 0x3 {short}

  mov a,r7

  add a,#0xfd

  mov r7,a

  mov a,r0

  addc a,#0xff

  mov r0,a

; _gint [lr0:0]{int} = _gint [lr0:0]{int} + iTemp17 
[lr23:38]{int}[r7 r0]

  mov a,r7

  add a,_gint

  mov _gint,a

  mov a,r0

  addc a,(_gint + 1)

  mov (_gint + 1),a

; iTemp21 [lr21:38]{short}[r4] = iTemp21 
[lr21:38]{short}[r4] + 0x1 {short}

  inc r4

; iTemp23 [lr22:38]{int}[r5 r6]= iTemp23 
[lr22:38]{int}[r5 r6]- 0x1 {short}

  dec r5

  cjne r5,#0xff,00104$

  dec r6

; goto _forcond_0($4)

  sjmp 00104$

; _forbreak_0($7) :

00107$:

; ret iTemp24 [lr40:41]{short}

  mov a,r3

  add a,r2

  mov dpl,a

; _return($8) :

00108$:

  ret


 A few words about basic block successors, predecessors 
  and dominators

Successors are basic blocks that might execute after 
this basic block.
Predecessors are basic blocks that might execute before 
reaching this basic block.
Dominators are basic blocks that WILL execute before 
reaching this basic block.


[basic block 1]

if (something)

    [basic block 2]

else

    [basic block 3]

[basic block 4]


a) succList of [BB2] = [BB4], of [BB3] = [BB4], of 
[BB1] = [BB2,BB3]

b) predList of [BB2] = [BB1], of [BB3] = [BB1], of 
[BB4] = [BB2,BB3]

c) domVect of [BB4] = BB1 ... here we are not sure if 
BB2 or BB3 was executed but we are SURE that BB1 was executed.

Acknowledgments

[http://sdcc.sourceforge.net#Who]

Thanks to all the other volunteer developers who have 
helped with coding, testing, web-page creation, 
distribution sets, etc. You know who you are :-)


This document was initially written by Sandeep Dutta

All product names mentioned herein may be trademarks of 
their respective companies. 

 Alphabetical index

To avoid confusion, the installation and building 
options for SDCC itself (chapter 2) are not part of the index.


