Copyright (c) 1993, 1994, 1995 Cygnus Support
Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies.
Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the entire resulting derived work is distributed under the terms of a permission notice identical to this one.
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Rough Draft
The goal of this document is to gather all the information needed to port the GNU tools to a new embedded target in one place. This will duplicate some info found in the other manual for the GNU tools, but this should be all you’ll need.
Next: Porting GCC, Previous: Embed with GNU, Up: Embed with GNU [Contents]
Libgloss is a library for all the details that usually get glossed over.
This library refers to things like startup code, and usually I/O support
for gcc
and C library
. The C library used through out
this manual is newlib
. Newlib is a ANSI conforming C library
developed by Cygnus Support. Libgloss could easily be made to
support other C libraries, and it can be used standalone as well. The
standalone configuration is typically used when bringing up new
hardware, or on small systems.
For a long time, these details were part of newlib. This approach worked well when a complete tool chain only had to support one system. A tool chain refers to the series of compiler passes required to produce a binary file that will run on an embedded system. For C, the passes are cpp, gcc, gas, ld. Cpp is the preprocessor, which process all the header files and macros. Gcc is the compiler, which produces assembler from the processed C files. Gas assembles the code into object files, and then ld combines the object files and binds the code to addresses and produces the final executable image.
Most of the time a tool chain does only have to support one target
execution environment. An example of this would be a tool chain for the
AMD 29k processor family. All of the execution environments for this
processor have the same interface, the same memory map, and the same
I/O code. In this case all of the support code is under newlib/libc/sys.
Libgloss’s creation was forced initially because of the cpu32
processor family. There are many different execution environments for
this line, and they vary wildly. newlib itself has only a few
dependencies that it needs for each target. These are explained later in
this doc. The hardware dependent part of newlib was reorganized into a
separate directory structure within newlib called the stub dirs. It was
initially called this because most of the routines newlib needs for a
target were simple stubs that do nothing, but return a value to the
application. They only exist so the linker can produce a final
executable image. This work was done during the early part of 1993.
After a while it became apparent that this approach of isolating the hardware and systems files together made sense. Around this same time the stub dirs were made to run standalone, mostly so it could also be used to support GDB’s remote debugging needs. At this time it was decided to move the stub dirs out of newlib and into it’s own separate library so it could be used standalone, and be included in various other GNU tools without having to bring in all of newlib, which is large. The new library is called Libgloss, for Gnu Low-level OS support.
Next: Configuring and building libgloss., Previous: Libgloss, Up: Libgloss [Contents]
Currently libgloss is being used for the following targets:
Next: Motorola CPU32 Targets supported, Up: Supported Targets [Contents]
This is for the Fujitsu Sparclite family of processors. Currently this covers the ex930, ex931, ex932, ex933, and the ex934. In addition to the I/O code a startup file, this has a GDB debug-stub that gets linked into your application. This is an exception handler style debug stub. For more info, see the section on Porting GDB. Porting GDB.
The Fujitsu eval boards use a host based terminal program to load and
execute programs on the target. This program, pciuh
is relatively
new (in 1994) and it replaced the previous ROM monitor which had the
shell in the ROM. GDB uses the the GDB remote protocol, the relevant
source files from the gdb sources are remote-sparcl.c. The debug stub is
part of libgloss and is called sparcl-stub.c.
Next: Mips core Targets Supported, Previous: Sparclite Targets Supported, Up: Supported Targets [Contents]
This refers to Motorola’s m68k based CPU32 processor family. The crt0.S
startup file should be usable with any target environment, and it’s
mostly just the I/O code and linker scripts that vary. Currently there
is support for the Motorola MVME line of 6U VME boards and IDP
line of eval boards. All of the
Motorola VME boards run Bug
, a ROM based debug monitor.
This monitor has the feature of using user level traps to do I/O, so
this code should be portable to other MVME boards with little if any
change. The startup file also can remain unchanged. About the only thing
that varies is the address for where the text section begins. This can
be accomplished either in the linker script, or on the command line
using the ‘-Ttext [address]’.
There is also support for the rom68k
monitor as shipped on
Motorola’s IDP eval board line. This code should be portable across the
range of CPU’s the board supports. There is also GDB support for this
target environment in the GDB source tree. The relevant files are
gdb/monitor.c, monitor.h, and rom58k-rom.c. The usage of these files is
discussed in the GDB section.
Next: PA-RISC Targets Supported, Previous: Motorola CPU32 Targets supported, Up: Supported Targets [Contents]
The Crt0 startup file should run on any mips target that doesn’t require
additional hardware initialization. The I/O code so far only supports a
custom LSI33k based RAID disk controller board. It should easy to
change to support the IDT line of eval boards. Currently the two
debugging protocols supported by GDB for mips targets is IDT’s mips
debug protocol, and a customized hybrid of the standard GDB remote
protocol and GDB’s standard ROM monitor support. Included here is the
debug stub for the hybrid monitor. This supports the LSI33k processor,
and only has support for the GDB protocol commands g
, G
,
m
, M
, which basically only supports the register and
memory reading and writing commands. This is part of libgloss and is
called lsi33k-stub.c.
The crt0.S should also work on the IDT line of eval boards, but has only
been run on the LSI33k for now. There is no I/O support for the IDT eval
board at this time. The current I/O code is for a customized version of
LSI’s pmon
ROM monitor. This uses entry points into the monitor,
and should easily port to other versions of the pmon monitor. Pmon is
distributed in source by LSI.
Previous: Mips core Targets Supported, Up: Supported Targets [Contents]
This supports the various boards manufactured by the HP-PRO consortium. This is a group of companies all making variations on the PA-RISC processor. Currently supported are ports to the WinBond ‘Cougar’ board based around their w89k version of the PA. Also supported is the Oki op50n processor.
There is also included, but never built an unfinished port to the HP 743 board. This board is the main CPU board for the HP700 line of industrial computers. This target isn’t exactly an embedded system, in fact it’s really only designed to load and run HP-UX. Still, the crt0.S and I/O code are fully working. It is included mostly because their is a barely functioning exception handler GDB debug stub, and I hope somebody could use it. The other PRO targets all use GDB’s ability to talk to ROM monitors directly, so it doesn’t need a debug stub. There is also a utility that will produce a bootable file by HP’s ROM monitor. This is all included in the hopes somebody else will finish it. :-)
Both the WinBond board and the Oki board download srecords. The WinBond board also has support for loading the SOM files as produced by the native compiler on HP-UX. WinBond supplies a set of DOS programs that will allow the loading of files via a bidirectional parallel port. This has never been tested with the output of GNU SOM, as this manual is mostly for Unix based systems.
Next: Adding Support for a New Board, Previous: Supported Targets, Up: Libgloss [Contents]
Libgloss uses an autoconf based script to configure. Autoconf scripts are portable shell scripts that are generated from a configure.in file. Configure input scripts are based themselves on m4. Most configure scripts run a series of tests to determine features the various supported features of the target. For features that can’t be determined by a feature test, a makefile fragment is merged in. The configure process leaves creates a Makefile in the build directory. For libgloss, there are only a few configure options of importance. These are –target and –srcdir.
Typically libgloss is built in a separate tree just for objects. In this manner, it’s possible to have a single source tree, and multiple object trees. If you only need to configure for a single target environment, then you can configure in the source tree. The argument for –target is a config string. It’s usually safest to use the full canonical opposed to the target alias. So, to configure for a CPU32 (m68k) with a separate source tree, use:
../src/libgloss/configure --verbose --target m68k-coff
The configure script is in the source tree. When configure is invoked it will determine it’s own source tree, so the –srcdir is would be redundant here.
Once libgloss is configured, make
is sufficient to build it. The
default values for Makefiles
are typically correct for all
supported systems. The test cases in the testsuite will also built
automatically as opposed to a make check
, where test binaries
aren’t built till test time. This is mostly cause the libgloss
testsuites are the last thing built when building the entire GNU source
tree, so it’s a good test of all the other compilation passes.
The default values for the Makefiles are set in the Makefile fragment merged in during configuration. This fragment typically has rules like
CC_FOR_TARGET = `if [ -f $${OBJROOT}/gcc/xgcc ] ; \ then echo ${OBJROOT}/gcc/xgcc -B${OBJROOT}/gcc/ ; \ else t='${program_transform_name}'; echo gcc | sed -e '' $$t ; fi`
Basically this is a runtime test to determine whether there are freshly
built executables for the other main passes of the GNU tools. If there
isn’t an executable built in the same object tree, then
transformedthe generic tool name (like gcc) is transformed to the
name typically used in GNU cross compilers. The names are
typically based on the target’s canonical name, so if you’ve configured
for m68k-coff
the transformed name is m68k-coff-gcc
in
this case. If you install with aliases or rename the tools, this won’t
work, and it will always look for tools in the path. You can force the a
different name to work by reconfiguring with the
--program-transform-name
option to configure. This option takes a
sed script like this -e s,^,m68k-coff-,
which produces tools
using the standard names (at least here at Cygnus).
The search for the other GNU development tools is exactly the same idea.
This technique gets messier when build options like -msoft-float
support are used. The Makefile fragments set the MUTILIB
variable, and if it is set, the search path is modified. If the linking
is done with an installed cross compiler, then none of this needs to be
used. This is done so libgloss will build automatically with a fresh,
and uninstalled object tree. It also makes it easier to debug the other
tools using libgloss’s test suites.
Previous: Configuring and building libgloss., Up: Libgloss [Contents]
This section explains how to add support for a new board to libgloss. In order to add support for a board, you must already have developed a toolchain for the target architecture.
All of the changes you will make will be in the subdirectory named after the architecture used by your board. For example, if you are developing support for a new ColdFire board, you will modify files in the m68k subdirectory, as that subdirectory contains support for all 68K devices, including architecture variants like ColdFire.
In general, you will be adding three components: a crt0.S file (see Crt0, the main startup file), a linker script (see Linker scripts for memory management), and a hardware support library. Each should be prefixed with the name of your board. For example, if you ard adding support for a new Surf board, then you will be adding the assembly surf-crt0.S (which will be assembled into surf-crt0.o), the linker script surf.ld, and other C and assembly files which will be combined into the hardware support library libsurf.a.
You should modify Makefile.in to define new variables corresponding to your board. Although there is some variation between architectures, the general convention is to use the following format:
# The name of the crt0.o file. SURF_CRT0 = surf-crt0.o # The name of the linker script. SURF_SCRIPTS = surf.ld # The name of the hardware support library. SURF_BSP = libsurf.a # The object files that make up the hardware support library. SURF_OBJS = surf-file1.o surf-file2.o # The name of the Makefile target to use for installation. SURF_INSTALL = install-surf
Then, you should create the ${SURF_BSP}
and
${SURF_INSTALL}
make targets. Add ${SURF_CRT0}
to
the dependencies for the all
target and add
${SURF_INSTALL}
to the dependencies for the install
target. Now, when libgloss is built and installed, support for your
BSP will be installed as well.
Next: Porting newlib, Previous: Libgloss, Up: Embed with GNU [Contents]
Porting GCC requires two things, neither of which has anything to do with GCC. If GCC already supports a processor type, then all the work in porting GCC is really a linker issue. All GCC has to do is produce assembler output in the proper syntax. Most of the work is done by the linker, which is described elsewhere.
Mostly all GCC does is format the command line for the linker pass. The
command line for GCC is set in the various config subdirectories of gcc.
The options of interest to us are CPP_SPEC
and
STARTFILE_SPEC
. CPP_SPEC sets the builtin defines for your
environment. If you support multiple environments with the same
processor, then OS specific defines will need to be elsewhere.
STARTFILE_SPEC
Once you have linker support, GCC will be able to produce a fully linked executable image. The only part of GCC that the linker wants is a crt0.o, and a memory map. If you plan on running any programs that do I/O of any kind, you’ll need to write support for the C library, which is described elsewhere.
Next: Options, Up: Porting GCC [Contents]
GCC by itself only compiles the C or C++ code into assembler. Typically
GCC invokes all the passes required for you. These passes are cpp, cc1,
gas, ld. cpp
is the C preprocessor. This will merge in the
include files, expand all macros definitions, and process all the
#ifdef
sections. To see the output of ccp, invoke gcc with the
-E
option, and the preprocessed file will be printed on the
stdout. cc1 is the actual compiler pass that produces the assembler for
the processed file. GCC is actually only a driver program for all the
compiler passes. It will format command line options for the other passes.
The usual command line GCC uses for the final link phase will have LD
link in the startup code and additional libraries by default.
GNU AS started it’s life to only function as a compiler pass, but
these days it can also be used as a source level assembler. When used as
a source level assembler, it has a companion assembler preprocessor
called gasp
. This has a syntax similar to most other assembler
macros packages. GAS emits a relocatable object file from the assembler
source. The object file contains the executable part of the application,
and debug symbols.
LD is responsible for resolving the addresses and symbols to something
that will be fully self-contained. Some RTOS’s use relocatable object
file formats like a.out
, but more commonly the final image will
only use absolute addresses for symbols. This enables code to be burned
into PROMS as well. Although LD can produce an executable image, there
is usually a hidden object file called crt0.o
that is required as
startup code. With this startup code and a memory map, the executable
image will actually run on the target environment. Startup
Files.
The startup code usually defines a special symbol like _start
that is the default base address for the application, and the first
symbol in the executable image. If you plan to use any routines from the
standard C library, you’ll also need to implement the functions that
this library is dependent on. Porting Newlib.
Previous: Compilation passes, Up: Porting GCC [Contents]
Options for the various development tools are covered in more detail elsewhere. Still, the amount of options can be an overwhelming amount of stuff, so the options most suited to embedded systems are summarized here. If you use GCC as the main driver for all the passes, most of the linker options can be passed directly to the compiler. There are also GCC options that control how the GCC driver formats the command line arguments for the linker.
Next: GAS Options, Up: Options [Contents]
Most of the GCC options that we’re interested control how the GCC driver formats the options for the linker pass.
-nostartfiles
-nostdlib
-Xlinker
Pass the next option directly to the linker.
-v
-fpic
Next: LD Options, Previous: GCC Options, Up: Options [Contents]
Previous: GAS Options, Up: Options [Contents]
Next: Writing a new GDB backend, Previous: Porting GCC, Up: Embed with GNU [Contents]
Next: Linker scripts for memory management, Up: Porting newlib [Contents]
To make a program that has been compiled with GCC to run, you need to write some startup code. The initial piece of startup code is called a crt0. (C RunTime 0) This is usually written in assembler, and it’s object gets linked in first, and bootstraps the rest of the application when executed. This file needs to do the following things.
If you plan to burn your code in a ROM, then the crt0 typically has to do all the hardware initialization that is required to run an application. This can include things like initializing serial ports or run a memory check. It all depends on the hardware.
When there is a ROM monitor present, usually a user trap can be called and then the ROM takes over. Pick a safe vector with no side effects. Some ROMs have a builtin trap handler just for this case.
portable between all the m68k based boards we have here. Example Crt0.S.
/* ANSI concatenation macros. */ #define CONCAT1(a, b) CONCAT2(a, b) #define CONCAT2(a, b) a ## b
These we’ll use later.
/* These are predefined by new versions of GNU cpp. */ #ifndef __USER_LABEL_PREFIX__ #define __USER_LABEL_PREFIX__ _ #endif /* Use the right prefix for global labels. */ #define SYM(x) CONCAT1 (__USER_LABEL_PREFIX__, x)
These macros are to make this code portable between both COFF and a.out. COFF always has an _ (underline) prepended on the front of all global symbol names. a.out has none.
#ifndef __REGISTER_PREFIX__ #define __REGISTER_PREFIX__ #endif /* Use the right prefix for registers. */ #define REG(x) CONCAT1 (__REGISTER_PREFIX__, x) #define d0 REG (d0) #define d1 REG (d1) #define d2 REG (d2) #define d3 REG (d3) #define d4 REG (d4) #define d5 REG (d5) #define d6 REG (d6) #define d7 REG (d7) #define a0 REG (a0) #define a1 REG (a1) #define a2 REG (a2) #define a3 REG (a3) #define a4 REG (a4) #define a5 REG (a5) #define a6 REG (a6) #define fp REG (fp) #define sp REG (sp)
This is for portability between assemblers. Some register names have a % or $ prepended to the register name.
/* * Set up some room for a stack. We just grab a chunk of memory. */ .set stack_size, 0x2000 .comm SYM (stack), stack_size
Set up space for the stack. This can also be done in the linker script, but it typically gets done here.
/* * Define an empty environment. */ .data .align 2 SYM (environ): .long 0
Set up an empty space for the environment. This is bogus on any most ROM monitor, but we setup a valid address for it, and pass it to main. At least that way if an application checks for it, it won’t crash.
.align 2 .text .global SYM (stack) .global SYM (main) .global SYM (exit) /* * This really should be __bss_start, not SYM (__bss_start). */ .global __bss_start
Setup a few global symbols that get used elsewhere. __bss_start needs to be unchanged, as it’s setup by the linker script.
/* * start -- set things up so the application will run. */ SYM (start): link a6, #-8 moveal #SYM (stack) + stack_size, sp /* * zerobss -- zero out the bss section */ moveal #__bss_start, a0 moveal #SYM (end), a1 1: movel #0, (a0) leal 4(a0), a0 cmpal a0, a1 bne 1b
The global symbol start
is used by the linker as the default
address to use for the .text
section. then it zeros the
.bss
section so the uninitialized data will all be cleared. Some
programs have wild side effects from having the .bss section let
uncleared. Particularly it causes problems with some implementations of
malloc
.
/* * Call the main routine from the application to get it going. * main (argc, argv, environ) * We pass argv as a pointer to NULL. */ pea 0 pea SYM (environ) pea sp@(4) pea 0 jsr SYM (main) movel d0, sp@-
Setup the environment pointer and jump to main()
. When
main()
returns, it drops down to the exit
routine below.
/* * _exit -- Exit from the application. Normally we cause a user trap * to return to the ROM monitor for another run. */ SYM (exit): trap #0
Implementing exit
here is easy. Both the rom68k
and bug
can handle a user caused exception of zero
with no side effects.
Although the bug
monitor has a user caused trap that will return
control to the ROM monitor, this solution has been more portable.
Next: What to do when you have a binary image, Previous: Crt0, the main startup file, Up: Porting newlib [Contents]
The linker script sets up the memory map of an application. It also
sets up default values for variables used elsewhere by sbrk() and the
crt0. These default variables are typically called _bss_start
and
_end
.
For G++, the constructor and destructor tables must also be setup here.
The actual section names vary depending on the object file format. For
a.out
and coff
, the three main sections are .text
,
.data
, and .bss
.
Now that you have an image, you can test to make sure it got the
memory map right. You can do this by having the linker create a memory
map (by using the -Map
option), or afterwards by using nm
to
check a few critical addresses like start
, bss_end
, and
_etext
.
Here’s a breakdown of a linker script for a m68k based target board.
See the file libgloss/m68k/idp.ld
, or go to the appendixes in
the end of the manual. Example Linker Script.
STARTUP(crt0.o) OUTPUT_ARCH(m68k) INPUT(idp.o) SEARCH_DIR(.) __DYNAMIC = 0;
The STARTUP
command loads the file specified so that it’s
first. In this case it also doubles to load the file as well, because
the m68k-coff configuration defaults to not linking in the crt0.o by
default. It assumes that the developer probably has their own crt0.o.
This behavior is controlled in the config file for each architecture.
It’s a macro called STARTFILE_SPEC
, and if it’s set to
null
, then when gcc
formats it’s command line, it doesn’t
add crto.o
. Any file name can be specified here, but the default
is always crt0.o
.
Course if you only use ld
to link, then the control of whether or
not to link in crt0.o
is done on the command line. If you have
multiple crto files, then you can leave this out all together, and link
in the crt0.o
in the makefile, or by having different linker
scripts. Sometimes this is done for initializing floating point
optionally, or to add device support.
The OUTPUT_ARCH
sets architecture the output file is for.
INPUT
loads in the file specified. In this case, it’s a relocated
library that contains the definitions for the low-level functions need
by libc.a. This could have also been specified on the command line, but
as it’s always needed, it might as well be here as a default.
SEARCH_DIR
specifies the path to look for files, and
_DYNAMIC
means in this case there are no shared libraries.
/* * Setup the memory map of the MC68ec0x0 Board (IDP) * stack grows up towards high memory. This works for * both the rom68k and the mon68k monitors. */ MEMORY { ram : ORIGIN = 0x10000, LENGTH = 2M }
This specifies a name for a section that can be referred to later in the script. In this case, it’s only a pointer to the beginning of free RAM space, with an upper limit at 2M. If the output file exceeds the upper limit, it will produce an error message.
/* * stick everything in ram (of course) */ SECTIONS { .text : { CREATE_OBJECT_SYMBOLS *(.text) etext = .; __CTOR_LIST__ = .; LONG((__CTOR_END__ - __CTOR_LIST__) / 4 - 2) *(.ctors) LONG(0) __CTOR_END__ = .; __DTOR_LIST__ = .; LONG((__DTOR_END__ - __DTOR_LIST__) / 4 - 2) *(.dtors) LONG(0) __DTOR_END__ = .; *(.lit) *(.shdata) } > ram .shbss SIZEOF(.text) + ADDR(.text) : { *(.shbss) }
Set up the .text
section. In a COFF
file, .text is where
all the actual instructions are. This also sets up the CONTRUCTOR
and the DESTRUCTOR tables for G++
. Notice that the section
description redirects itself to the ram variable setup earlier.
.talias : { } > ram .data : { *(.data) CONSTRUCTORS _edata = .; } > ram
Setup the .data
section. In a coff
file, this is where all
he initialized data goes. CONSTRUCTORS
is a special command used
by ld
.
.bss SIZEOF(.data) + ADDR(.data) : { __bss_start = ALIGN(0x8); *(.bss) *(COMMON) end = ALIGN(0x8); _end = ALIGN(0x8); __end = ALIGN(0x8); } .mstack : { } > ram .rstack : { } > ram .stab . (NOLOAD) : { [ .stab ] } .stabstr . (NOLOAD) : { [ .stabstr ] } }
Setup the .bss
section. In a COFF
file, this is where
unitialized data goes. The symbols _bss_start
and _end
are setup here for use by the crt0.o
when it zero’s the
.bss
section.
Next: Libraries, Previous: Linker scripts for memory management, Up: Porting newlib [Contents]
A few ROM monitors load binary images, typically a.out
, but most all
will load an srecord
. An srecord is an ASCII representation of a binary
image. At it’s simplest, an srecord is an address, followed by a byte
count, followed by the bytes, and a 2’s compliment checksum. A whole
srecord file has an optional start record, and a required end
record. To make an srecord from a binary image, the GNU objcopy
program
is used. This will read the image and make an srecord from it. To do
this, invoke objcopy like this: objcopy -O srec infile outfile
. Most
PROM burners also read srecords or a similar format. Use objdump -i
to
get a list of support object files types for your architecture.
Previous: What to do when you have a binary image, Up: Porting newlib [Contents]
This describes newlib
, a freely available libc replacement. Most
applications use calls in the standard C library. When initially linking
in libc.a, several I/O functions are undefined. If you don’t plan on
doing any I/O, then you’re OK, otherwise they need to be created. These
routines are read, write, open, close. sbrk, and kill. Open & close
don’t need to be fully supported unless you have a filesystems, so
typically they are stubbed out. Kill is also a stub, since you can’t do
process control on an embedded system.
Sbrk() is only needed by applications that do dynamic memory
allocation. It’s uses the symbol _end
that is setup in the linker
script. It also requires a compile time option to set the upper size
limit on the heap space. This leaves us with read and write, which are
required for serial I/O. Usually these two routines are written in C,
and call a lower level function for the actual I/O operation. These two
lowest level I/O primitives are inbyte() and outbyte(), and are also
used by GDB back ends if you’ve written an exception handler. Some
systems also implement a havebyte() for input as well.
Other commonly included functions are routines for manipulating LED’s on the target (if they exist) or low level debug help. Typically a putnum() for printing words and bytes as a hex number is helpful, as well as a low-level print() to output simple strings.
As libg++ uses the I/O routines in libc.a, if read and write work, then libg++ will also work with no additional changes.
Next: Misc support routines, Previous: Making I/O work, Up: Libraries [Contents]
To support using any of the memory functions, you need to implement
sbrk(). malloc()
, calloc()
, and realloc()
all call
sbrk()
at there lowest level. caddr_t
is defined elsewhere
as char *
. RAMSIZE
is presently a compile time option. All
this does is move a pointer to heap memory and check for the upper
limit. Example libc support code. sbrk()
returns a
pointer to the previous value before more memory was allocated.
/* _end is set in the linker command file * extern caddr_t _end;/ /* just in case, most boards have at least some memory */ #ifndef RAMSIZE # define RAMSIZE (caddr_t)0x100000 #endif /* * sbrk -- changes heap size size. Get nbytes more * RAM. We just increment a pointer in what's * left of memory on the board. */ caddr_t sbrk(nbytes) int nbytes; { static caddr_t heap_ptr = NULL; caddr_t base; if (heap_ptr == NULL) { heap_ptr = (caddr_t)&_end; } if ((RAMSIZE - heap_ptr) >= 0) { base = heap_ptr; heap_ptr += nbytes; return (base); } else { errno = ENOMEM; return ((caddr_t)-1); } }
Next: Useful debugging functions, Previous: Routines for dynamic memory allocation, Up: Libraries [Contents]
These are called by newlib
but don’t apply to the embedded
environment. isatty()
is self explanatory. kill()
doesn’t
apply either in an environment withno process control, so it justs
exits, which is a similar enough behavior. getpid()
can safely
return any value greater than 1. The value doesn’t effect anything in
newlib
because once again there is no process control.
/* * isatty -- returns 1 if connected to a terminal device, * returns 0 if not. Since we're hooked up to a * serial port, we'll say yes and return a 1. */ int isatty(fd) int fd; { return (1); } /* * getpid -- only one process, so just return 1. */ #define __MYPID 1 int getpid() { return __MYPID; } /* * kill -- go out via exit... */ int kill(pid, sig) int pid; int sig; { if(pid == __MYPID) _exit(sig); return 0; }
Previous: Misc support routines, Up: Libraries [Contents]
There are always a few useful functions for debugging your project in
progress. I typically implement a simple print()
routine that
runs standalone in liblgoss, with no newlib
support. The I/O
function outbyte()
can also be used for low level debugging. Many
times print will work when there are problems that cause printf()
to
cause an exception. putnum()
is just to print out values in hex
so they are easier to read.
/* * print -- do a raw print of a string */ int print(ptr) char *ptr; { while (*ptr) { outbyte (*ptr++); } } /* * putnum -- print a 32 bit number in hex */ int putnum (num) unsigned int num; { char buffer[9]; int count; char *bufptr = buffer; int digit; for (count = 7 ; count >= 0 ; count--) { digit = (num >> (count * 4)) & 0xf; if (digit <= 9) *bufptr++ = (char) ('0' + digit); else *bufptr++ = (char) ('a' - 10 + digit); } *bufptr = (char) 0; print (buffer); return; }
If there are LEDs on the board, they can also be put to use for
debugging when the serial I/O code is being written. I usually implement
a zylons()
function, which strobes the LEDS (if there is more
than one) in sequence, creating a rotating effect. This is convenient
between I/O to see if the target is still alive. Another useful LED
function is led_putnum()
, which takes a digit and displays it as
a bit pattern or number. These usually have to be written in assembler
for each target board. Here are a number of C based routines that may be
useful.
led_putnum()
puts a number on a single digit segmented
LED display. This LED is set by setting a bit mask to an address, where
1 turns the segment off, and 0 turns it on. There is also a little
decimal point on the LED display, so it gets the leftmost bit. The other
bits specify the segment location. The bits look like:
[d.p | g | f | e | d | c | b | a ] is the byte.
The locations are set up as:
a ----- f | | b | g | ----- | | e | | c ----- d
This takes a number that’s already been converted to a string, and prints it.
#define LED_ADDR 0xd00003 void led_putnum ( num ) char num; { static unsigned char *leds = (unsigned char *)LED_ADDR; static unsigned char num_bits [18] = { 0xff, /* clear all */ 0xc0, 0xf9, 0xa4, 0xb0, 0x99, 0x92, 0x82, 0xf8, 0x80, 0x98, /* numbers 0-9 */ 0x98, 0x20, 0x3, 0x27, 0x21, 0x4, 0xe /* letters a-f */ }; if (num >= '0' && num <= '9') num = (num - '0') + 1; if (num >= 'a' && num <= 'f') num = (num - 'a') + 12; if (num == ' ') num = 0; *leds = num_bits[num]; } /* * zylons -- draw a rotating pattern. NOTE: this function never returns. */ void zylons() { unsigned char *leds = (unsigned char *)LED_ADDR; unsigned char curled = 0xfe; while (1) { *leds = curled; curled = (curled >> 1) | (curled << 7); delay ( 200 ); } }
Next: Binutils, Previous: Porting newlib, Up: Embed with GNU [Contents]
Typically, either the low-level I/O routines are used for debugging, or LEDs, if present. It is much easier to use GDb for debugging an application. There are several different techniques used to have GDB work remotely. Commonly more than one kind of GDB interface is used to cober a wide variety of development needs.
The most common style of GDB backend is an exception handler for
breakpoints. This is also called a gdb stub, and is requires the
two additional lines of init code in your main()
routine. The GDB
stubs all use the GDB remote protocol. When the application gets a
breakpoint exception, it communicates to GDB on the host.
Another common style of interfacing GDB to a target is by using an existing ROM monitor. These break down into two main kinds, a similar protocol to the GDB remote protocol, and an interface that uses the ROM monitor directly. This kind has GDB simulating a human operator, and all GDB does is work as a command formatter and parser.
The standard remote protocol is a simple, packet based scheme. A debug packet whose contents are <data> is encapsulated for transmission in the form:
$ <data> # CSUM1 CSUM2
<data> must be ASCII alphanumeric and cannot include characters
$
or #
. If <data> starts with two characters
followed by :
, then the existing stubs interpret this as a
sequence number. For example, the command g
is used to read the
values of the registers. So, a packet to do this would look like
$g#67
CSUM1 and CSUM2 are an ascii representation in hex of an 8-bit checksum of <data>, the most significant nibble is sent first. the hex digits 0-9,a-f are used.
A simple protocol is used when communicating with the target. This is
mainly to give a degree of error handling over the serial cable. For
each packet transmitted successfully, the target responds with a
+
(ACK
). If there was a transmission error, then the target
responds with a -
(NAK
). An error is determined when the
checksum doesn’t match the calculated checksum for that data record.
Upon reciept of the ACK
, GDB
can then transmit the next
packet.
Here is a list of the main functions that need to be supported. Each data
packet is a command with a set number of bytes in the command packet.
Most commands either return data, or respond with a NAK
. Commands
that don’t return data respond with an ACK
. All data values are
ascii hex digits. Every byte needs two hex digits to represent t. This
means that a byte with the value ‘7’ becomes ‘07’. On a 32 bit
machine this works out to 8 characters per word. All of the bytes in a
word are stored in the target byte order. When writing the host side of
the GDB protocol, be careful of byte order, and make sure that the code
will run on both big and little endian hosts and produce the same answers.
These functions are the minimum required to make a GDB backend work. All other commands are optional, and not supported by all GDB backends.
g
’returns XXXXXXXX...
Registers are in the internal order for GDB, and the bytes in a register
are in the same order the machine uses. All values are in sequence
starting with register 0. All registers are listed in the same packet. A
sample packet would look like $g#
.
GXXXXXXXX...
’XXXXXXXX
is the value to set the register to. Registers are in
the internal order for GDB, and the bytes in a register are in the same
order the machine uses. All values are in sequence starting with
register 0. All registers values are listed in the same packet. A sample
packet would look like $G000000001111111122222222...#
returns ACK
or NAK
mAAAAAAAA,LLLL
’AAAAAAAA
is address, LLLL
is length. A sample packet would
look like $m00005556,0024#
. This would request 24 bytes starting
at address 00005556
returns XXXXXXXX...
XXXXXXXX
is the memory contents. Fewer bytes than requested will
be returned if only part of the data can be read. This can be determined
by counting the values till the end of packet #
is seen and
comparing that with the total count of bytes that was requested.
MAAAAAAAA,LLLL:XXXXXXXX
’AAAAAAAA
is the starting address, LLLL
is the number of
bytes to be written, and XXXXXXXX
is value to be written. A
sample packet would look like
$M00005556,0024:101010101111111100000000...#
returns ACK
or NAK
for an error. NAK
is also
returned when only part of the data is written.
cAAAAAAAAA
’AAAAAAAA
is address to resume execution at. If AAAAAAAA
is
omitted, resume at the curent address of the pc
register.
returns the same replay as last signal
. There is no immediate
replay to cont
until the next breakpoint is reached, and the
program stops executing.
AA..AA
is address to resume
If AA..AA
is omitted, resume at same address.
returns the same replay as last signal
. There is no immediate
replay to step
until the next breakpoint is reached, and the
program stops executing.
?
’This returns one of the following:
SAA
Where AA
is the number of the last signal.
Exceptions on the target are converted to the most similar Unix style
signal number, like SIGSEGV
. A sample response of this type would
look like $S05#
.
AA
is the signal number.
nn
is the register number.
XXXXXXXX
is the register value.
AA
is the exit status. This is only
applicable for certains sorts of targets.
These are used in some GDB backends, but not all.
Pnn=XXXXXXXX
’Write register nn
with value XXXXXXXX
.
returns ACK
or NAK
toggle debug flag (see 386 & 68k stubs)
reset – see sparc stub.
other
’On other requests, the stub should ignore the request and send an empty
response $#<checksum>
. This way we can extend the protocol and GDB
can tell whether the stub it is talking to uses the old or the new.
tAA:PP,MM
’Search backwards starting at address AA
for a match with pattern
PP and mask MM
. PP
and MM
are 4 bytes.
qXXXX
’Request info about XXXX.
QXXXX=yyyy
’Set value of XXXX
to yyyy
.
qOffsets
’Get section offsets. Reply is Text=xxx;Data=yyy;Bss=zzz
Send text to stdout. The text gets display from the target side of the serial connection.
Responses can be run-length encoded to save space. A *
means that
the next character is an ASCII encoding giving a repeat count which
stands for that many repetitions of the character preceding the *
.
The encoding is n+29, yielding a printable character where n >=3
(which is where run length encoding starts to win). You can’t use a
value of where n >126 because it’s only a two byte value. An example
would be a 0*03
means the same thing as 0000
.
Next: Using a ROM monitor as a backend, Previous: The standard remote protocol, Up: Writing a new GDB backend [Contents]
A GDB stub consists of two parts, support for the exception handler, and the exception handler itself. The exception handler needs to communicate to GDB on the host whenever there is a breakpoint exception. When GDB starts a program running on the target, it’s polling the serial port during execution looking for any debug packets. So when a breakpoint occurs, the exception handler needs to save state, and send a GDB remote protocol packet to GDB on the host. GDB takes any output that isn’t a debug command packet and displays it in the command window.
Support for the exception handler varies between processors, but the minimum supported functions are those needed by GDB. These are functions to support the reading and writing of registers, the reading and writing of memory, start execution at an address, single step, and last signal. Sometimes other functions for adjusting the baud rate, or resetting the hardware are implemented.
Once GDB gets the command packet from the breakpoint, it will read a few
registers and memory locations an then wait for the user. When the user
types run
or continue
a continue
command is issued
to the backend, and control returns from the breakpoint routine to the
application.
Next: Adding support for new protocols, Previous: A linked in exception handler, Up: Writing a new GDB backend [Contents]
GDB also can mimic a human user and use a ROM monitors normal debug
commands as a backend. This consists mostly of sending and parsing
ASCII
strings. All the ROM monitor interfaces share a common set
of routines in gdb/monitor.c
. This supports adding new ROM
monitor interfaces by filling in a structure with the common commands
GDB needs. GDb already supports several command ROM monitors, including
Motorola’s Bug
monitor for their VME boards, and the Rom68k
monitor by Integrated Systems, Inc. for various m68k based boards. GDB
also supports the custom ROM monitors on the WinBond and Oki PA based
targets. There is builtin support for loading files to ROM monitors
specifically. GDB can convert a binary into an srecord and then load it
as an ascii file, or using xmodem
.
Previous: Using a ROM monitor as a backend, Up: Writing a new GDB backend [Contents]
Next: Code Listings, Previous: Writing a new GDB backend, Up: Embed with GNU [Contents]
Next: Linker script for the IDP board, Previous: Binutils, Up: Embed with GNU [Contents]
Next: crt0.S - The startup file, Previous: Code Listings, Up: Code Listings [Contents]
This is the linker script script that is used on the Motorola IDP board.
STARTUP(crt0.o) OUTPUT_ARCH(m68k) INPUT(idp.o) SEARCH_DIR(.) __DYNAMIC = 0; /* * Setup the memory map of the MC68ec0x0 Board (IDP) * stack grows up towards high memory. This works for * both the rom68k and the mon68k monitors. */ MEMORY { ram : ORIGIN = 0x10000, LENGTH = 2M } /* * stick everything in ram (of course) */ SECTIONS { .text : { CREATE_OBJECT_SYMBOLS *(.text) etext = .; __CTOR_LIST__ = .; LONG((__CTOR_END__ - __CTOR_LIST__) / 4 - 2) *(.ctors) LONG(0) __CTOR_END__ = .; __DTOR_LIST__ = .; LONG((__DTOR_END__ - __DTOR_LIST__) / 4 - 2) *(.dtors) LONG(0) __DTOR_END__ = .; *(.lit) *(.shdata) } > ram .shbss SIZEOF(.text) + ADDR(.text) : { *(.shbss) } .talias : { } > ram .data : { *(.data) CONSTRUCTORS _edata = .; } > ram .bss SIZEOF(.data) + ADDR(.data) : { __bss_start = ALIGN(0x8); *(.bss) *(COMMON) end = ALIGN(0x8); _end = ALIGN(0x8); __end = ALIGN(0x8); } .mstack : { } > ram .rstack : { } > ram .stab . (NOLOAD) : { [ .stab ] } .stabstr . (NOLOAD) : { [ .stabstr ] } }
Next: C based "glue" code., Previous: Linker script for the IDP board, Up: Code Listings [Contents]
/* * crt0.S -- startup file for m68k-coff * */ .title "crt0.S for m68k-coff" /* These are predefined by new versions of GNU cpp. */ #ifndef __USER_LABEL_PREFIX__ #define __USER_LABEL_PREFIX__ _ #endif #ifndef __REGISTER_PREFIX__ #define __REGISTER_PREFIX__ #endif /* ANSI concatenation macros. */ #define CONCAT1(a, b) CONCAT2(a, b) #define CONCAT2(a, b) a ## b /* Use the right prefix for global labels. */ #define SYM(x) CONCAT1 (__USER_LABEL_PREFIX__, x) /* Use the right prefix for registers. */ #define REG(x) CONCAT1 (__REGISTER_PREFIX__, x) #define d0 REG (d0) #define d1 REG (d1) #define d2 REG (d2) #define d3 REG (d3) #define d4 REG (d4) #define d5 REG (d5) #define d6 REG (d6) #define d7 REG (d7) #define a0 REG (a0) #define a1 REG (a1) #define a2 REG (a2) #define a3 REG (a3) #define a4 REG (a4) #define a5 REG (a5) #define a6 REG (a6) #define fp REG (fp) #define sp REG (sp) /* * Set up some room for a stack. We just grab a chunk of memory. */ .set stack_size, 0x2000 .comm SYM (stack), stack_size /* * Define an empty environment. */ .data .align 2 SYM (environ): .long 0 .align 2 .text .global SYM (stack) .global SYM (main) .global SYM (exit) /* * This really should be __bss_start, not SYM (__bss_start). */ .global __bss_start /* * start -- set things up so the application will run. */ SYM (start): link a6, #-8 moveal #SYM (stack) + stack_size, sp /* * zerobss -- zero out the bss section */ moveal #__bss_start, a0 moveal #SYM (end), a1 1: movel #0, (a0) leal 4(a0), a0 cmpal a0, a1 bne 1b /* * Call the main routine from the application to get it going. * main (argc, argv, environ) * We pass argv as a pointer to NULL. */ pea 0 pea SYM (environ) pea sp@(4) pea 0 jsr SYM (main) movel d0, sp@- /* * _exit -- Exit from the application. Normally we cause a user trap * to return to the ROM monitor for another run. */ SYM (exit): trap #0
Next: I/O assembler code sample, Previous: crt0.S - The startup file, Up: Code Listings [Contents]
/* * glue.c -- all the code to make GCC and the libraries run on * a bare target board. These should work with any * target if inbyte() and outbyte() exist. */ #include <sys/types.h> #include <sys/stat.h> #include <errno.h> #ifndef NULL #define NULL 0 #endif /* FIXME: this is a hack till libc builds */ __main() { return; } #undef errno int errno; extern caddr_t _end; /* _end is set in the linker command file */ extern int outbyte(); extern unsigned char inbyte(); extern int havebyte(); /* just in case, most boards have at least some memory */ #ifndef RAMSIZE # define RAMSIZE (caddr_t)0x100000 #endif /* * read -- read bytes from the serial port. Ignore fd, since * we only have stdin. */ int read(fd, buf, nbytes) int fd; char *buf; int nbytes; { int i = 0; for (i = 0; i < nbytes; i++) { *(buf + i) = inbyte(); if ((*(buf + i) == '\n') || (*(buf + i) == '\r')) { (*(buf + i)) = 0; break; } } return (i); } /* * write -- write bytes to the serial port. Ignore fd, since * stdout and stderr are the same. Since we have no filesystem, * open will only return an error. */ int write(fd, buf, nbytes) int fd; char *buf; int nbytes; { int i; for (i = 0; i < nbytes; i++) { if (*(buf + i) == '\n') { outbyte ('\r'); } outbyte (*(buf + i)); } return (nbytes); } /* * open -- open a file descriptor. We don't have a filesystem, so * we return an error. */ int open(buf, flags, mode) char *buf; int flags; int mode; { errno = EIO; return (-1); } /* * close -- close a file descriptor. We don't need * to do anything, but pretend we did. */ int close(fd) int fd; { return (0); } /* * sbrk -- changes heap size size. Get nbytes more * RAM. We just increment a pointer in what's * left of memory on the board. */ caddr_t sbrk(nbytes) int nbytes; { static caddr_t heap_ptr = NULL; caddr_t base; if (heap_ptr == NULL) { heap_ptr = (caddr_t)&_end; } if ((RAMSIZE - heap_ptr) >= 0) { base = heap_ptr; heap_ptr += nbytes; return (base); } else { errno = ENOMEM; return ((caddr_t)-1); } } /* * isatty -- returns 1 if connected to a terminal device, * returns 0 if not. Since we're hooked up to a * serial port, we'll say yes and return a 1. */ int isatty(fd) int fd; { return (1); } /* * lseek -- move read/write pointer. Since a serial port * is non-seekable, we return an error. */ off_t lseek(fd, offset, whence) int fd; off_t offset; int whence; { errno = ESPIPE; return ((off_t)-1); } /* * fstat -- get status of a file. Since we have no file * system, we just return an error. */ int fstat(fd, buf) int fd; struct stat *buf; { errno = EIO; return (-1); } /* * getpid -- only one process, so just return 1. */ #define __MYPID 1 int getpid() { return __MYPID; } /* * kill -- go out via exit... */ int kill(pid, sig) int pid; int sig; { if(pid == __MYPID) _exit(sig); return 0; } /* * print -- do a raw print of a string */ int print(ptr) char *ptr; { while (*ptr) { outbyte (*ptr++); } } /* * putnum -- print a 32 bit number in hex */ int putnum (num) unsigned int num; { char buffer[9]; int count; char *bufptr = buffer; int digit; for (count = 7 ; count >= 0 ; count--) { digit = (num >> (count * 4)) & 0xf; if (digit <= 9) *bufptr++ = (char) ('0' + digit); else *bufptr++ = (char) ('a' - 10 + digit); } *bufptr = (char) 0; print (buffer); return; }
Next: I/O code sample, Previous: C based "glue" code., Up: Code Listings [Contents]
/* * mvme.S -- board support for m68k */ .title "mvme.S for m68k-coff" /* These are predefined by new versions of GNU cpp. */ #ifndef __USER_LABEL_PREFIX__ #define __USER_LABEL_PREFIX__ _ #endif #ifndef __REGISTER_PREFIX__ #define __REGISTER_PREFIX__ #endif /* ANSI concatenation macros. */ #define CONCAT1(a, b) CONCAT2(a, b) #define CONCAT2(a, b) a ## b /* Use the right prefix for global labels. */ #define SYM(x) CONCAT1 (__USER_LABEL_PREFIX__, x) /* Use the right prefix for registers. */ #define REG(x) CONCAT1 (__REGISTER_PREFIX__, x) #define d0 REG (d0) #define d1 REG (d1) #define d2 REG (d2) #define d3 REG (d3) #define d4 REG (d4) #define d5 REG (d5) #define d6 REG (d6) #define d7 REG (d7) #define a0 REG (a0) #define a1 REG (a1) #define a2 REG (a2) #define a3 REG (a3) #define a4 REG (a4) #define a5 REG (a5) #define a6 REG (a6) #define fp REG (fp) #define sp REG (sp) #define vbr REG (vbr) .align 2 .text .global SYM (_exit) .global SYM (outln) .global SYM (outbyte) .global SYM (putDebugChar) .global SYM (inbyte) .global SYM (getDebugChar) .global SYM (havebyte) .global SYM (exceptionHandler) .set vbr_size, 0x400 .comm SYM (vbr_table), vbr_size /* * inbyte -- get a byte from the serial port * d0 - contains the byte read in */ .align 2 SYM (getDebugChar): /* symbol name used by m68k-stub */ SYM (inbyte): link a6, #-8 trap #15 .word inchr moveb sp@, d0 extbl d0 unlk a6 rts /* * outbyte -- sends a byte out the serial port * d0 - contains the byte to be sent */ .align 2 SYM (putDebugChar): /* symbol name used by m68k-stub */ SYM (outbyte): link fp, #-4 moveb fp@(11), sp@ trap #15 .word outchr unlk fp rts /* * outln -- sends a string of bytes out the serial port with a CR/LF * a0 - contains the address of the string's first byte * a1 - contains the address of the string's last byte */ .align 2 SYM (outln): link a6, #-8 moveml a0/a1, sp@ trap #15 .word outln unlk a6 rts /* * outstr -- sends a string of bytes out the serial port without a CR/LF * a0 - contains the address of the string's first byte * a1 - contains the address of the string's last byte */ .align 2 SYM (outstr): link a6, #-8 moveml a0/a1, sp@ trap #15 .word outstr unlk a6 rts /* * havebyte -- checks to see if there is a byte in the serial port, * returns 1 if there is a byte, 0 otherwise. */ SYM (havebyte): trap #15 .word instat beqs empty movel #1, d0 rts empty: movel #0, d0 rts /* * These constants are for the MVME-135 board's boot monitor. They * are used with a TRAP #15 call to access the monitor's I/O routines. * they must be in the word following the trap call. */ .set inchr, 0x0 .set instat, 0x1 .set inln, 0x2 .set readstr, 0x3 .set readln, 0x4 .set chkbrk, 0x5 .set outchr, 0x20 .set outstr, 0x21 .set outln, 0x22 .set write, 0x23 .set writeln, 0x24 .set writdln, 0x25 .set pcrlf, 0x26 .set eraseln, 0x27 .set writd, 0x28 .set sndbrk, 0x29 .set tm_ini, 0x40 .set dt_ini, 0x42 .set tm_disp, 0x43 .set tm_rd, 0x44 .set redir, 0x60 .set redir_i, 0x61 .set redir_o, 0x62 .set return, 0x63 .set bindec, 0x64 .set changev, 0x67 .set strcmp, 0x68 .set mulu32, 0x69 .set divu32, 0x6A .set chk_sum, 0x6B
Next: Led control sample, Previous: I/O assembler code sample, Up: Code Listings [Contents]
#include "w89k.h" /* * outbyte -- shove a byte out the serial port. We wait till the byte */ int outbyte(byte) unsigned char byte; { while ((inp(RS232REG) & TRANSMIT) == 0x0) { } ; return (outp(RS232PORT, byte)); } /* * inbyte -- get a byte from the serial port */ unsigned char inbyte() { while ((inp(RS232REG) & RECEIVE) == 0x0) { }; return (inp(RS232PORT)); }
Previous: I/O code sample, Up: Code Listings [Contents]
/* * leds.h -- control the led's on a Motorola mc68ec0x0 board. */ #ifndef __LEDS_H__ #define __LEDS_H__ #define LED_ADDR 0xd00003 #define LED_0 ~0x1 #define LED_1 ~0x2 #define LED_2 ~0x4 #define LED_3 ~0x8 #define LED_4 ~0x10 #define LED_5 ~0x20 #define LED_6 ~0x40 #define LED_7 ~0x80 #define LEDS_OFF 0xff #define LEDS_ON 0x0 #define FUDGE(x) ((x >= 0xa && x <= 0xf) ? (x + 'a') & 0x7f : (x + '0') & 0x7f) extern void led_putnum( char ); #endif /* __LEDS_H__ */ /* * leds.c -- control the led's on a Motorola mc68ec0x0 (IDP)board. */ #include "leds.h" void zylons(); void led_putnum(); /* * led_putnum -- print a hex number on the LED. the value of num must be a char with * the ascii value. ie... number 0 is '0', a is 'a', ' ' (null) clears * the led display. * Setting the bit to 0 turns it on, 1 turns it off. * the LED's are controlled by setting the right bit mask in the base * address. * The bits are: * [d.p | g | f | e | d | c | b | a ] is the byte. * * The locations are: * * a * ----- * f | | b * | g | * ----- * | | * e | | c * ----- * d . d.p (decimal point) */ void led_putnum ( num ) char num; { static unsigned char *leds = (unsigned char *)LED_ADDR; static unsigned char num_bits [18] = { 0xff, /* clear all */ 0xc0, 0xf9, 0xa4, 0xb0, 0x99, 0x92, 0x82, 0xf8, 0x80, 0x98, /* numbers 0-9 */ 0x98, 0x20, 0x3, 0x27, 0x21, 0x4, 0xe /* letters a-f */ }; if (num >= '0' && num <= '9') num = (num - '0') + 1; if (num >= 'a' && num <= 'f') num = (num - 'a') + 12; if (num == ' ') num = 0; *leds = num_bits[num]; } /* * zylons -- draw a rotating pattern. NOTE: this function never returns. */ void zylons() { unsigned char *leds = (unsigned char *)LED_ADDR; unsigned char curled = 0xfe; while (1) { *leds = curled; curled = (curled >> 1) | (curled << 7); delay ( 200 ); } }