Embedded Linux intro

The slides from the lecture today in elbit added to Embedded linux page

most of the slides taken from the great site: http://www.free-electrons.com

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OSK board tutorial

The embedded linux tutorial using the ARM starter kit is completed.
the Embedded linux section is updated

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Embedded Linux - Loading The Kernel

Now we are ready to operate the board
we want to load the kernel inside the board flash memory and mount the file system in out host computer. this is very useful in the development process because the only thing we should do to download out application/driver to the target is to copy it from one directory to another on the host computer

restart the device and press a key to get u-boot shell
the easiest way to load files from host to target is to use tftp server on the host.
start the tftp server and place the kernel image (uImage.cc) in the server directory

on the target uboot shell:

# setenv serverip [your tftp server ip address]
# tftpboot 0x10000000 uImage.cc
after this you will get a number in hex format - REMEMBER IT

now we should erase the flash memory : (bank 8 to 20)

# erase 1:8-20
# cp.b 0x10000000 0x100000 [the number above]

now set the bootargs variable:

# setenv bootargs console=ttyS0,115200n8 noinitrd ip=${OSK_IP}:
${PC_IP}:${GATEWAY_IP}:${NETMASK}:osk:eth0:off root=
/dev/nfs rw nfsroot=${PC_IP}:/data/rootfs2.6,nolock mem=32M
# saveenv

to test the board restart it or:

# bootm 0x100000

after all the messages , you will get a prompt with the file system on the host

now you can use the toolchain to build applications and drivers, copy the output files to the root filesystem directory and execute/load it from the target


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Embedded Linux - Root File System

The next step in to build a root file system.
there are many ways to do that. we are using busybox
busybox creates a single file that implements many tools from the file system
you can download it and configure it using "make menuconfig"
the only thing you should remember is to copy the .so files from the lib directory in your toolchain (usr/local/arm/3.4.1/arm-linux/lib) to the lib directory in the root file system

for already made file system click here

after creating the file system place it in a directory and update the file /etc/exports with access rights :

/opt/osk/rootfs2.6 *(rw,no_root_squash)

restart the nfs server

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Embedded Linux - building the kernel

The next step is to build the kernel with our toolchain
you should download the kernel source and a patch

download kernel 2.6.20 (from http://www.kernel.org/)
download the board kernel patch

now follow this:

# tar -xjvf ${DOWLOADDIR}/linux-${VERSION}.tar.bz2
# cp ${DOWLOADDIR}/patch-${VERSION}-omap1.bz2 .
# bunzip2 patch-${VERSION}-omap1.bz2
# cd linux-${VERSION}/
# cat ../patch-${VERSION}-omap1 | patch -p1

# make clean
# make omap_osk_5912_defconfig

make sure that the following options are set:
CONFIG_NFS_FS=y
CONFIG_NFS_V3=y
CONFIG_ROOT_NFS=y


# make

now the kernel image is ready but we have to convert it to U-BOOT format

# arm-linux-objcopy -O binary -R .note -R .comment S
arch/arm/boot/compressed/vmlinux linux.bin
# gzip -9 linux.bin
# ${U-BOOTDIR}/tools/mkimage -A arm -O linux -T kernel -C gzip -a 0x10c08000 -e 0x10c08000 -n Linux Kernel Image -d linux.bin.gz uImage.cc

uImage.cc is ready

for already made uImage.cc click here


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visit our site: Bina

Embedded Linux - boot loader

The next step in our osk system is to build and set the boot loader
the OSK board comes with already installed U-BOOT,
we can replace it but we don't need
we do need a tool: mkimage to convert the kernel image to U_BOOT format
to build the tool download U-BOOT source

do the following:

# tar -xjvf ${DOWLOADDIR}/u-boot-1.1.2.tar.bz2
# cd u-boot-1.1.2
# make distclean
# make omap5912osk_config
# make tools

you can also run make to create the binary image of u-boot boot loader so you can replace it on the board but we don't need it (future post)

if you look inside the tools directory you will find the tool mkimage



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Embedded Linux - Toolchain

The next step for our OSK system is to find or create a toolchain
we need a toolchain for ARM processor

Building a new toolchain can be complicated mission
in general you should download:

• binutils - http://ftp.gnu.org/gnu/binutils/
• gcc - http://ftp.gnu.org/gnu/gcc/
• C library - http://ftp.gnu.org/gnu/glibc/
• some extensions

then configure and build a binary image of your toolschain (future post)
for our purpose we can use an already made toolchain from here

extract the archive:

# tar -xjvf ${DOWLOADDIR}/arm-linux-gcc-3.4.1.tar.bz2

look at the path: ${EXTRACTEDDIR}/usr/local/arm/3.4.1/bin
(all the binary tools to compile, link and debug an ARM code)

add the above path to your PATH environment variable :

# export PATH=/usr/local/arm/3.4.1/bin/:$PATH

now we can build everything with this toolchain

for help and other learning materials
visit our site: Bina

Embedded Linux - Connecting to the device

The device (osk5912) comes with a system based on kernel 2.4
the next step is to connect it using RS232 (null modem cable) to your host machine
to see the device terminal you can use windows or linux

On Windows Host
use hyperterminal : set the connection to the correct COM port with the following settings: 115200 baud, no parity, 8 data bits, 1 stop bit , no flow control
connect the device to power and push the reset button on it (small white button)

On Linux Host
first setup minicom

# minicom -s

select serial port setup
set the following:

• Serial device - /dev/ttyS0 (or other number based on your com port)
• Bps/pas/Bits - 115200 8N1
• No software flow
• No hardware flow

save setting and Exit (to minicom)

(the setup step is required only once so next time just run minicom)

push the reset button on the board

You can now play with the system and with some demos provided from MontaVista

We dont want to use kernel 2.4 and also want to build our system with free software so we will not use Montavista distribution

Note: The porpose of this posts is to study embedded linux and thats why we dont use the commercial distribution. there is no real free software, if you use Montavista or other commercial distribution you pay (around 15000$ for developer) but you get full support and much work have been done for you (BSP,device drivers and sample programs). when you use the "free" tools you have to spend time to solve problems and creating the BSP and you know - "time is money"

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Embedded Linux - Setting up host

the first thing to do is setting your host machine
Install one of the Linux desktop distributions on your host
make sure that it includes:

• C/C++ development tools
• NFS server

I'm using Open SUSE 10 on one workstation and fedora code 3 on another

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Embedded Linux - Starter Kit

To deal with a real system you should buy the OSK 5912 Board
to buy it go to: this site

the board is based on ARM processor with DSP Processor and you can evaluate also Montavista distribution (kernel 2.4)

we will use it to with only free software tools includes:

• Toolchain
• Boot loader
• Kernel
• Root file system

for help and other learning materials
visit our site: Bina

Embedded Linux - Overview

Linux is great for embedded systems, also for real-time but with some constraints
The perfect way to learn it is by doing it yourself with step by step instructions
here we will post some articles to help new embedded linux developers
enjoy

for help and other learning materials
visit our site: Bina