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Intro to Embedded Linux Programming
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Linux Users Los Angeles
21 October 2003
*Draft*

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Dan Kegel


www.kegel.com
www.lalugs.org

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Programming Embedded Linux


	Embedded Systems Developers Love Linux
	Accessing Embedded Linux
	Installing a Cross-Toolchain on your PC
	Compiling C/C++ Programs For Embedded Linux
	Building Embedded Linux from Scratch
	Summary / Questions

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Embedded Systems Developers Love Linux

Linux is the OS of choice for new embedded systems

	Highly reliable, customizable, royalty-free

	Huge base of existing software

	New protocols often developed for Linux first

	Open Source -> you can fix problems yourself

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Getting At Embedded Linux

Many devices officially support running Linux programs
	Handheld barcode scanners
	Upcoming cellphones from Motorola and Samsung
	Ixia network testers

Others only support it unofficially or unwillingly :-)
	The TiVo personal video recorder
	Linksys routers

Once you have a login prompt on the device, you're in business

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Yes, Virginia, you have to cross-compile

Embedded Linux mindshare of top six CPU types 
(2002 LinuxDevices.com developer poll):
	x86	- 32%
	Arm	- 27% (e.g. Linksys)
	PowerPC	- 16% (e.g. TiVo 1)
	MIPS	-  9% (e.g. Linksys, TiVo 2)
	SH	-  5% (e.g. Dreamcast)
	Coldfire-  4% (e.g. Snapgear)

To reach most of the market, you need to cross-compile!
Most open-source software supports being cross-compiled
(though you may have to nudge it a bit)

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Installing a Cross-Toolchain on your PC

First, identify which CPU and C library the device uses

Log in to the device and ask it what CPU it has, e.g.
    $ uname -m
or
    $ cat /proc/cpuinfo
That should display the CPU type (e.g. i386, ppc, arm, mips, sh, m68k...)

Then guess the C library type with the command
    $ ls /lib/*libc-*
If you see libuClibc-0.9.8.so, the device uses uClibc-0.9.8.
If you see libc-2.2.5.so, the device uses glibc-2.2.5.

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Installing a Cross-Toolchain -- glibc

One easy way:

   wget www.kegel.com/crosstool/crosstool-0.24.tar.gz
   tar -xzvf crosstool-0.24.tar.gz
   cd crosstool-0.24
   export PREFIX=/mygcc 
   eval `cat ppc405.dat` `cat gcc3.3.1-glibc2.3.2.dat` all.sh

CPU and glibc version must match those of the device!

Toolchain problems may require expertise to solve 

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Compiling C/C++ Programs For Embedded Linux -- Hello, World!

Put the toolchain's bin directory on your PATH, e.g.
    $ PATH=${PATH}:/mygcc/bin

Then instead of cc, use the cross-compiler to compile, e.g.
    $ ppc-405-linux-gnu-gcc hello.c

Projects using Makefiles can usually be compiled like this:
    $ make CC=ppc-405-linux-gnu-gcc
though you should read and understand the Makefile first.

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Compiling C/C++ Programs For Embedded Linux -- autoconf

Many open source projects use configure scripts.  Some need overrides when cross-compiling, e.g.

    $ export ac_cv_func_setpgrp_void=yes 
    $ ./configure --target=ppc-405-linux-gnu --build=i686-linux

This generates a Makefile with CC=ppc-405-linux-gnu-gcc

Autoconf is complex; read its tutorials and macro library!

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Building Embedded Linux from Scratch

Cross-compiling not standardized; each package different

Best practices dictate that you script the cross-compile

Laziness dictates that you use someone else's scripts :-)

ptxdist is a collection of Makefiles, one per package,
so you don't have to reinvent the wheel
"make menuconfig" picks which programs to install
Supports about 80 packages so far (e.g. strace, nmap, oprofile, inetutils...)

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Summary 

Embedded Linux is becoming ubiquitous

Embedded Linux tools are getting easier to set up and use

Distributions like ptxdist make building custom
embedded Linux systems from scratch easier

Some Embedded Linux devices let end users run their own 
programs built with Embedded Linux tools

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Links

Slides for this talk
     www.kegel.com/linux/embed

Crosstool
    http://kegel.com/crosstool/

ptxdist
    http://www.pengutronix.de/software/ptxdist_en.html


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Questions 

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Questions?

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Legal stuff

Copyright (C) 2003, Dan Kegel

All rights reserved