Linux initcpio tutorial

Tutorial for creating and using a Linux kernel with an initcpio initial RAM filesystem. Some notes are specific to the Gumstix Overo, but the ideia is the same for any other embedded platform.

• 1. Partitioning memory card

  2. Boot files

  3. Creating initcpio image

  4. Running programs on the remote host

  5. Cross-compiling programs statically

  6. Cross-compiling OpenCV

Partitioning memory card

Create two partitions on the memory card, one small 16MB FAT16 for the boot files, the other with FAT32 for storage (logs, etc...):

# fdisk /dev/sdx Command: d (delete existing partitions) Command: n (add a new partition) Command action: p (primary partition) Partition number (1-4): 1 First cylinder (1-yyy, default 1): 1 Last cylinder (1-yyy, default yyy): +16M Command: t (change a partition's system id) Hex code: 6 (FAT16) Command: a (toggle a bootable flag) Partition number (1-4): 1 Command: n (add a new partition) Command action: p (primary partition) Partition number (1-4): 2 First cylinder (xxx-yyy, default xxx): xxx Last cylinder (xxx-yyy, default yyy): yyy Command: t (change a partition's system id) Partition number (1-4): 2 Hex code: c (W95 FAT32 LBA) Command: w (write table to disk and exit) # dd if=/dev/zero of=/dev/sdx1 bs=512 count=1 # mkdosfs /dev/sdx1 # dd if=/dev/zero of=/dev/sdx2 bs=512 count=1 # mkdosfs /dev/sdx2

Boot files

Copy the boot loader files, the Linux image and the initcpio image to the boot partition of the memory card.

Gumstix Overo

# mount -t msdos /dev/sdx1 /mnt # cp linux/overo/MLO /mnt/mlo (boot loader boot loader) # cp linux/overo/u-boot.bin /mnt (boot loader) # cp linux/overo/boot.scr /mnt (boot loader script) # cp linux/overo/uImage /mnt/uimage (Linux kernel image) # cp initcpio/overo/initcpio.img /mnt (initcpio image) # umount /mnt

After this, the memory card is ready: insert it in the Gumstix Overo and it should boot into Linux automatically.

To generate the boot.scr file, edit the boot.txt file and then run make. Here is a Makefile:

boot.scr: boot.txt mkimage -T script -C none -A arm -O linux -d $+ $@

And here is a boot.txt:

setenv bootargs mt9v032.auto_exp=0 fatload mmc 0 82000000 uImage fatload mmc 0 83000000 initcpio.img bootm 82000000 83000000

To generate the initcpio.img file, see below.

Creating initcpio image

Generate the initcpio.img file.

Gumstix Overo

Requires the gen_init_cpio program (linux/usr/gen_init_cpio.c) and the mkimage program (uboot-mkimage Debian package).

$ cd initcpio/gen_init_cpio $ make $ cd initcpio/overo $ make

Here is a Makefile for the latter:

gen_init_cpio = ../gen_init_cpio/gen_init_cpio all: $(gen_init_cpio) list | gzip -9 >initcpio.gz mkimage -T ramdisk -C gzip -A arm -O linux -d initcpio.gz initcpio.img $(RM) initcpio.gz

Description of the initcpio/ files:

• • overo/list - list of files used by gen_init_cpio to generate the initcpio image (see the gen_init_cpio.c source code for the specification of the list file)

  • overo/init - sh script run by Linux at startup

  • overo/hotplug - sh script run by Linux at run time in response to an event (module load, firmware load request, device plug in/out, etc...)

  • bin/arm - utility programs statically built for ARM processors

  • bin/all - platform-independent binary files (firmwares, etc...)

Sample list file:

dir bin 0755 0 0 file bin/ftpd ../bin/arm/ftpd 0555 0 0 file bin/gzip ../bin/arm/gzip 0555 0 0 file bin/reaper ../bin/arm/reaper 0555 0 0 file bin/rshd ../bin/arm/rshd 0555 0 0 file bin/sh ../bin/arm/uutils 0555 0 0 bin/_reboot bin/cat bin/date bin/dosfsck bin/echo bin/ifconfig bin/iwconfig bin/mount bin/nice bin/pkill bin/sleep bin/umount dir boot 0755 0 0 dir dev 0755 0 0 nod dev/mmcblk0p1 0600 0 0 b 179 1 nod dev/mmcblk0p2 0600 0 0 b 179 2 nod dev/null 0666 0 0 c 1 3 nod dev/ttyS2 0600 0 0 c 4 66 nod dev/ttyUSB0 0600 0 0 c 188 0 nod dev/video0 0600 0 0 c 81 0 file init init 0555 0 0 dir lib 0755 0 0 dir lib/firmware 0755 0 0 file lib/firmware/sd8686.bin ../bin/all/sd8686.bin 0444 0 0 file lib/firmware/sd8686_helper.bin ../bin/all/sd8686_helper.bin 0444 0 0 dir proc 0755 0 0 dir sbin 0755 0 0 file sbin/hotplug hotplug 0555 0 0 dir sys 0755 0 0

Sample init file:

#!/bin/sh exec /dev/null 2>/dev/null mount -t proc proc /proc mount -t sysfs sysfs /sys ifconfig lo 127.0.0.1 up ifconfig eth0 192.168.1.1 up rshd & nice ftpd & exec nice reaper

Sample hotplug file:

#!/bin/sh case $SUBSYSTEM in net) case $INTERFACE in wlan0) case $ACTION in add) iwconfig wlan0 essid myrouter ifconfig wlan0 192.168.2.1 up ;; remove) ifconfig wlan0 down esac esac ;; firmware) case $ACTION in add) echo 1 >/sys/$DEVPATH/loading cat /lib/firmware/$FIRMWARE >/sys/$DEVPATH/data echo 0 >/sys/$DEVPATH/loading esac esac

Running programs on the remote host

To run a program on a running Gumstix Overo, remotely from your computer, is a three step process: cross-compile the program statically, upload the program to the bin/ directory on the RAM of the Gumstix Overo, and remotely run the program with the necessary arguments if any:

$ make $ curl -sST ${program} ftp://${ipaddress}/bin/ $ rsh ${ipaddress} ${program} ${arguments}...

Requires the curl and rsh programs (curl and rsh-client Debian packages).

Cross-compiling programs statically

Gumstix Overo

The easiest way is to install the ARM cross-compiler toolchain in Ubuntu 10.10 (other versions will not work)! Install the g++-arm-linux-gnueabi package, and apt-get will automaticaly install all the dependencies packages.

Then just write a Makefile to use the arm-linux-gnueabi- toolchain. Example:

CROSS = arm-linux-gnueabi- CC = $(CROSS)gcc CXX = $(CROSS)g++ CFLAGS = -Wall -O3 -mcpu=cortex-a8 -mfpu=neon -mfloat-abi=softfp -ffast-math CXXFLAGS = $(CFLAGS) LDFLAGS = -static -s

Cross-compiling OpenCV

Steps to cross-compile OpenCV and install it in OpenCV-x.y.z-install.

First create a toolchain-arm.cmake file:

SET(CMAKE_SYSTEM_NAME Linux) SET(CMAKE_C_COMPILER arm-linux-gnueabi-gcc) SET(CMAKE_CXX_COMPILER arm-linux-gnueabi-g++)

Then unpack OpenCV, cross-compile it and install it:

$ tar xjf OpenCV-2.3.0.tar.bz2 $ mkdir OpenCV-2.3.0-{build,install} $ cd OpenCV-2.3.0-build $ cmake -DCMAKE_TOOLCHAIN_FILE=../toolchain-arm.cmake \ -DCMAKE_INSTALL_PREFIX=../OpenCV-2.3.0-install \ -DBUILD_SHARED_LIBS=OFF ../OpenCV-2.3.0 $ make -j2 $ make install $ cp 3rdparty/lib/liblibjasper.a ../OpenCV-2.3.0-install/lib/libjasper.a $ cp 3rdparty/lib/liblibjpeg.a ../OpenCV-2.3.0-install/lib/libjpeg.a $ cp 3rdparty/lib/liblibpng.a ../OpenCV-2.3.0-install/lib/libpng.a $ cp 3rdparty/lib/liblibtiff.a ../OpenCV-2.3.0-install/lib/libtiff.a $ cp 3rdparty/lib/libzlib.a ../OpenCV-2.3.0-install/lib/libz.a

Now, to link your programs with this cross-compiled OpenCV, you can use a Makefile like this:

OPENCV = ../OpenCV-2.3.0-install CXX = arm-linux-gnueabi-g++ CXXFLAGS = -Wall -O3 CPPFLAGS = -I$(OPENCV)/include -I$(OPENCV)/include/opencv LDFLAGS += $(OPENCV)/lib/libopencv_core.a LDFLAGS += $(OPENCV)/lib/libopencv_highgui.a LDFLAGS += $(OPENCV)/lib/libjasper.a LDFLAGS += $(OPENCV)/lib/libpng.a LDFLAGS += $(OPENCV)/lib/libtiff.a LDFLAGS += $(OPENCV)/lib/libjpeg.a LDFLAGS += $(OPENCV)/lib/libz.a LDFLAGS += -lrt -lpthread LDFLAGS += -static -s

Aug 7 2011

Andre B. Oliveira