Getting started with embedded-linux

Remarks#

This section provides an overview of what embedded-linux is, and why a developer might want to use it.

It should also mention any large subjects within embedded-linux, and link out to the related topics. Since the Documentation for embedded-linux is new, you may need to create initial versions of those related topics.

Installation or Setup

Detailed instructions on getting embedded-linux set up or installed.

ARM Versatile Express Emulation On Qemu

Environment Introduction:

Host ubuntu :- 12.04

Linux kernel version: linux-4.4

busybox version: 1.24.0

Cross compiler tool chain: arm-2014.05-29-arm-none-linux-gnueabi-i686-pc-linux gnu.tar.bz2

qemu version: qemu-2.5

Download and Installation of QEMU:

$ mkdir Source_Code
$ cd Source_Code
$ git clone git://git.qemu-project.org/qemu.git
$ cd qemu
$ git checkout remotes/origin/stable-2.5 -b stable-2.5
$ cd ../../
$ mkdir -p Binary_images/Qemu_Bin
$ cd Qemu_src/qemu
$ cd Source_Code/qemu
$ ./configure --target-list=arm-softmmu --prefix=/Path/to/your/Binary_images/Qemu_Bin
$ make
$ make install

ARM Cross_Compiler Tool chain installation:

Download Source code: https://sourcery.mentor.com/public/gnu_toolchain/arm-none-linux-gnueabi/

Download –> arm-2014.05-29-arm-none-linux-gnueabi-i686-pc-linux-gnu.tar.bz2

$ mkdir -p Binary_images/ARM_Cross_Tools
$ cd Binary_images/ARM_Cross_Tools
$ tar xvf arm-2014.05-29-arm-none-linux-gnueabi-i686-pc-linux-gnu.tar.bz2

Download Linux kernel source code :

$ cd Source_Code
$ git clone https://github.com/torvalds/linux
$ cd linux
# Switch to version v4.4
$ git checkout v4.4

Prepare for compilation: Load default config for target board i.e vexpress_defconfig.

$ make ARCH=arm CROSS_COMPILE=/path/to/your/Binary_images/ARM_Cross_Tools/arm-2014.05/bin/arm-none-linux-gnueabi- vexpress_defconfig

Adjust or enable some settings as of now not required in future it might required.

$ make ARCH=arm CROSS_COMPILE=path to your/Binary_images/ARM_Cross_Tools/arm-2014.05/bin/arm-none-linux-gnueabi- menuconfig

Compile the kernel

$ make ARCH=arm CROSS_COMPILE=/path/to/your/Binary_images/ARM_Cross_Tools/arm-2014.05/bin/arm-none-linux-gnueabi- all

Verify qemu and kernel can run successfully:

~/Binary_images/Qemu_Bin/qemu-system-arm -M vexpress-a9 -m 512M -dtb ./arch/arm/boot/dts/vexpress-v2p-ca9.dtb -kernel ./arch/arm/boot/zImage -append “console=ttyAMA0” -serial stdio

Compiling Busybox for ARM on QEMU :

Download Busybox from https://busybox.net/downloads/

$ cd busybox
$ make ARCH=arm CROSS_COMPILE=/path/to/your/Binary_images/ARM_Cross_Tools/arm-2014.05/bin/arm-none-linux-gnueabi- defconfig

Enable or disable some settings as mentioned below

$make ARCH=arm CROSS_COMPILE=/path/to/your/Binary_images/ARM_Cross_Tools/arm-2014.05/bin/arm-none-linux-gnueabi- menuconfig

Busybox Settings —> Build Options —>

[*] Build BusyBox as a static binary (no shared libs)

$ make ARCH=arm CROSS_COMPILE=/path/to/your/Binary_images/ARM_Cross_Tools/arm-2014.05/bin/arm-none-linux-gnueabi- install

The above command builds Busybox and creates a directory called _install containing the root filesystem tree. Next, you need to create folder for mounting Virtual file systems like proc, sys and init scripts.

$ mkdir -p _install/proc/
$ mkdir -p _install/sys/
$ mkdir -p _install/tmp/
$ mkdir -p _install/root/
$ mkdir -p _install/var/
$ mkdir -p _install/mnt/
$ mkdir -p _install/etc/init.d/

Create a file name rcS inside folder _install/etc/init.d/ and edit rcS file with below content

#!/bin/sh
PATH=/sbin:/bin:/usr/sbin:/usr/bin
runlevel=S
prevlevel=N
umask 022
export PATH runlevel prevlevel
mount -a
echo /sbin/mdev /proc/sys/kernel/hotplug
mdev -s

Create a file name inittab inside _install/etc/ and edit it with below content.

# /etc/inittab
::sysinit:/etc/init.d/rcS
console::askfirst:-/bin/sh
::ctrlaltdel:/sbin/reboot
::shutdown:/bin/umount -a -r
::restart:/sbin/init

Download and copy fstab file to /etc/. folder in rootfs

$ wget clone https://github.com/mahadevvinay/Embedded_Stuff/tree/master/Embedded_Linux_Virtual_Setup/fstab

Create ext3 image file and Copy all the files in our _install folder to image:

$ dd if=/dev/zero of=RootFS.ext3 bs=1M count=$((32))
$ sudo mkfs.ext3 RootFS.ext3
$ mkdir tmpfs
$ sudo mount -t ext3 RootFS.ext3 tmpfs/ -o loop
$ sudo cp -r _install/* tmpfs/.
$ sudo umount tmpfs

The complete command is to emulate:

~/Qemu_/Binary_images/Qemu_Bin/bin/qemu-system-arm -M vexpress-a9 -dtb path to your linux folder/arch/arm/boot/dts/vexpress-v2p-ca9.dtb -kernel path to your linux folder/arch/arm/boot/zImage -append root=/dev/mmcblk0 console=ttyAMA0 -sd path to your busybox-1.24.0/RootFS.ext3 -serial stdio

The above setup is for Qemu, same procedure can be used to setup any Embedded Target.