CM-T3530: Linux: Kernel

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Overview

Linux kernel for CM-T3530 modules provides support for on-board peripherals and abstracts the functionality provided by the hardware. Current support coverage is specified at O/S support coverage map 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 CM-T3530 modules. Most of the CM-T3530 functionality is merged into the mainline kernel. CM-T3530 support is included in linux-omap git repository and will be merged into upcoming Linux kernel 2.6.33.

Kernel command line

The Linux kernel for CM-T3530 is shipped with built-in command line parameters:

ubi.mtd=4,2048 root=ubi0:cm-t35-rootfs rootfstype=ubifs console=ttyS2,115200 \
  omapfb.mode=dvi:1024x768-24@60 omapfb.vram=1:4M vram=8M  omapdss.def_disp=lcd

The default kernel command line defines primary console, default display settings, root device and root filesystem type.

Setting U-Boot bootargs environment variable overrides default kernel command line and can be used to set desired kernel parameters.

Building kernel for CM-T3530

Cross-Compiler

There are several options for cross-compilation toolchain setup. You can either compile your cross-compiler or use an already built cross-compiler. The cross-compiler should support the ARM embedded-application binary interface ("EABI")

  • Pre-built toolchain:
  • Tools for creating cross-compilers:
    • Crosstool-ng: Builds a cross-compiler from source. Non-distribution specific.
    • Crossdev: Gentoo's cross-compiler builder. Needs Gentoo.

U-Boot mkimage tool

U-Boot mkimage utility is required in order to create kernel images that can be loaded by the CM-T3530 bootloader. You can download prebuilt 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

There are two ways to get Linux kernel sources that can be used as a baseline for CM-T3530 kernel. You can create a copy of linux-omap git tree or download a snapshot and extract it. We assume that you have created /home/development/cm-t35/kernel directory for CM-T3530 kernel development

Snapshot download

  • Download v2.6.32-omap1 snapshot with your web browser. Note, that tools like wget and curl will not work here.
  • Extract the downloaded archive linux-omap-2.6-2a20002a83ce565ed16aaec5e64151cae165cb8f.tar.gz
cd /home/development/cm-t35/kernel
tar xzvf /path/to/downloaded/linux-omap-2.6-2a20002a83ce565ed16aaec5e64151cae165cb8f.tar.gz
This will create /home/development/cm-t35/kernel/linux-omap-2.6 directory containing linux-omap kernel tree.
  • Apply the CM-T3530 patch
cd /home/development/cm-t35/kernel/linux-omap-2.6
patch -p1 < /path/to/t3530-linux/kernel/linux-2.6.32-omap1-cm-t35.patch

Git clone

  • Install git version control system.
  • Create a clone of linux-omap kenrel tree
cd /home/development/cm-t35/kernel
git clone git://git.kernel.org/pub/scm/linux/kernel/git/tmlind/linux-omap-2.6.git linux-omap-2.6
  • Create a branch for CM-T3530 development. The CM-T3530 patches are generated vs. commit 2a20002a83ce565ed16aaec5e64151cae165cb8f in the linux-omap tree. It is recommended to use exactly the same baseline to avoid merge conflicts.
git checkout -b cm-t35-dev 2a20002a83ce565ed16aaec5e64151cae165cb8f
  • Apply the CM-T3530 patch
cd /home/development/cm-t35/kernel/linux-omap-2.6
git apply /path/to/t3530-linux/kernel/linux-2.6.32-omap1-cm-t35.patch

Building the kernel

export ARCH=arm
export CROSS_COMPILE=arm-none-linux-eabi-
make cm_t35_defconfig
make menuconfig
make && make uImage && \
     INSTALL_MOD_PATH=/home/development/cm-t35/rootfs make modules_install

In the example above, the Linux kernel image (uImage) will be created in /home/development/cm-t35/kernel/linux-omap-2.6/arch/arm/boot, and the loadable kernel modules will be installed into the /home/development/cm-t35/rootfs/lib/modules directory.

Now, if you boot CM-T3530 with newly created kernel image and with networked root filesysem at /home/development/cm-t35/rootfs/ the system will be able to properly load kernel modules and you avoid modules versioning problems.

See also