CM-T3530: Linux: Kernel
Contents
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 starting from 2.6.33 release.
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-2011.09
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-2a20002.tar.gz
cd /home/development/cm-t35/kernel tar xzvf /path/to/downloaded/linux-omap-2a20002.tar.gz
- This will create /home/development/cm-t35/kernel/linux-omap directory containing linux-omap kernel tree.
- Apply the CM-T3530 patch
cd /home/development/cm-t35/kernel/linux-omap patch -p1 < /path/to/t3530-linux/kernel/linux-2.6.32-cm-t35-3.patch
Git clone
- Install git version control system.
- Create a clone of linux-omap kernel tree
cd /home/development/cm-t35/kernel git clone git://git.kernel.org/pub/scm/linux/kernel/git/tmlind/linux-omap.git linux-omap
- 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 git apply /path/to/t3530-linux/kernel/linux-2.6.32-cm-t35-3.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/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 filesystem at /home/development/cm-t35/rootfs/ the system will be able to properly load kernel modules and you avoid modules versioning problems.
Power management
The Linux kernel for CM-T3530 supports very low power sleep mode and dynamic frequency scaling. Please refer to CM-T3530: Linux: Power management article for further details.
