Trim-Slice Linux Kernel

From Trim-Slice Wiki

Overview

The Trim-Slice Linux kernel provides support for on-board peripherals and abstracts the functionality provided by the hardware. Currently supported features are specified at the Supported Features page. CompuLab provides ready-to-run binary kernel images, and source code of the modifications and additions made to the Linux kernel to work properly with the Trim-Slice.

Kernel boot process

Default boot process

The Trim-Slice U-Boot scans the various boot devices and loads the kernel from the first valid boot device. The boot device is valid when:

physically present
formatted with ext2/ext3 or vfat
has uImage and boot.scr files in / or in /boot directory

Default boot device layout

The Trim-Slice default boot device layout:

/boot/uImage - Trim-Slice Linux kernel
/boot/boot.scr - U-Boot boot script that selects correct kernel boot parameters and loads the kernel
/ - root file system

Boot device scan order

The boot script (/boot/boot.scr) will attempt to boot from the various boot devices according to the following order:

Front SD card
External USB storage
Micro-SD card
Internal SATA storage

Custom boot process

The default Trim-Slice boot process can be overridden by setting custom bootargs and bootcmd U-boot variables:

bootargs variable

This variable defines kernel command line:

mem=384M@0M mem=512M@512M nvmem=128M@384M vmalloc=248M video=tegrafb console=ttyS0,115200

For internal SATA add:

root=/dev/sda1 nohdparm rootwait rw

For micro-SD add:

root=/dev/mmcblk0p1 rw

For NFS add:

root=/dev/nfs nfsroot=your_host:/your_rootfs_path,v3 ip=dhcp rw

bootcmd variable

This variable defines kernel load mechanism:

For internal SATA set:

usb start 1 && ext2load usb 0:1 4080000 /boot/uImage && bootm 4080000

For micro-SD set:

mmc init 1 && ext2load mmc 1 4080000 /boot/uImage && bootm 4080000

For TFTP boot set:

dhcp; setenv serverip your_server_ip; tftp 4080000 uImage; bootm 4080000

Building the Trim-Slice kernel

Cross-Compiler

For Trim-Slice kernel compilation we recommend to use CodeSourcery 2009-q1 cross-compiler. Install the cross-compiler by following the instructions below:

cd /home/development/cross-tools/
wget http://www.codesourcery.com/sgpp/lite/arm/portal/package4571/public/arm-none-linux-gnueabi/arm-2009q1-203-arm-none-linux-gnueabi-i686-pc-linux-gnu.tar.bz2
tar xvjf arm-2009q1-203-arm-none-linux-gnueabi-i686-pc-linux-gnu.tar.bz2

U-Boot mkimage tool

The U-Boot mkimage utility creates kernel images that can be loaded by the Trim-Slice boot-loader. You can download the pre-built mkimage binary or build it yourself:

mkdir ~/tmp
cd tmp
wget ftp://ftp.denx.de/pub/u-boot/u-boot-latest.tar.bz2
tar -xjvf u-boot-latest.tar.bz2
cd u-boot-2009.08
touch include/config.{h,mk}
make tools
sudo install tools/mkimage /usr/local/bin

Getting kernel sources

The Trim-Slice kernel is publicly available on gitorious.org hosting. There are two ways to get Linux kernel sources that can be used as a baseline for Trim-Slice kernel. You can either create a copy of trimslice-kernel git tree or download a snapshot and extract it.

The following instructions assume that you have created /home/development/trimslice/trimslice-kernel directory for Trim-Slice kernel sources.

Snapshot download

Download the latest release trimslice-l4t.r15.01 tag snapshot with your web browser.
Extract the downloaded archive into the /home/development/trimslice/trimslice-kernel directory.

Git clone

Install git version control system.
Create a clone of trimslice-kernel tree

cd /home/development/trimslice/
git clone git@gitorious.org:trimslice-kernel/trimslice-kernel.git trimslice-kernel

Create a branch for Trim-Slice development using the latest trimslice-l4t.r15.01 release tag

cd trimslice-kernel
git checkout -b trimslice/l4t.r15.01-dev trimslice-l4t.r15.01

Building the kernel

In the example below, the Linux kernel image (uImage) will be created in trimslice-kernel/arch/arm/boot, and the loadable kernel modules will be installed into the trimslice-kernel/modules_install/lib/modules directory.

export ARCH=arm
export CROSS_COMPILE=arm-none-linux-gnueabi-
export PATH=${PATH}:"/home/development/cross-tools/arm-2009q1/bin/"

cd /home/development/trimslice/trimslice-kernel
make trimslice_defconfig
make uImage 
make modules 
INSTALL_MOD_PATH=./modules_install make modules_install

Deploying the kernel

Copy /home/development/trimslice/trimslice-kernel/arch/arm/boot/uImage into the boot device /boot directory.
Copy /home/development/trimslice/trimslice-kernel/modules_install/ into the boot device / directory.