CM-T3730: Linux: Kernel
Contents
Overview
Linux kernel for CM-T3730 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-T3730 modules. Most of the CM-T3730 functionality is merged into the mainline kernel starting from 3.1 release.
Kernel command line
The Linux kernel for CM-T3730 is shipped with built-in command line parameters:
root=/dev/mmcblk0p3 rootwait console=ttyO2,115200 omapfb.mode=dvi:1024x768-24@60 omapfb.vram=1:4M vram=8M
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-T3730
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 (recommended):
- 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-T3730 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-<version>
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-T3730 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-t3730/kernel directory for CM-T3730 kernel development.
Snapshot download
- Download v3.0 snapshot with your web browser. Note, that tools like wget and curl will not work here.
- Extract the downloaded archive linux-02f8c6a.tar.gz
cd /home/development/cm-t3730/kernel tar xzvf /path/to/downloaded/linux-02f8c6a.tar.gz mv linux-02f8c6a linux-cm-t3730
- This will create /home/development/cm-t3730/kernel/linux-cm-t3730 directory containing linux kernel tree.
- Apply the CM-T3730 patch
cd /home/development/cm-t3730/kernel/linux-cm-t3730 patch -p1 < /path/to/t3730-linux/kernel/linux-3.0-cm-t3730-1.patch
- Copy the CM-T3730 kernel configuration file
cd /home/development/cm-t3730/kernel/linux-cm-t3730 cp /path/to/t3730-linux/kernel/linux-3.0-cm-t3730-1.defconfig arch/arm/configs/cm_t3730_defconfig
Git clone
- Install git version control system.
- Create a clone of linux kernel tree
cd /home/development/cm-t3730/kernel git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git linux-cm-t3730
- Create a branch for CM-T3730 development. The CM-T3730 patches are generated vs. v3.0 tag (02f8c6aee8df3cdc935e9bdd4f2d020306035dbe commit) in the linux tree. It is recommended to use exactly the same baseline to avoid merge conflicts.
git checkout -b cm-t3730-dev v3.0
- Apply the CM-T3730 patch
cd /home/development/cm-t3730/kernel/linux-cm-t3730 git apply /path/to/t3730-linux/kernel/linux-3.0-cm-t3730-1.patch
- Copy the CM-T3730 kernel configuration file
cd /home/development/cm-t3730/kernel/linux-cm-t3730 cp /path/to/t3730-linux/kernel/linux-3.0-cm-t3730-1.defconfig arch/arm/configs/cm_t3730_defconfig
Building the kernel
export ARCH=arm
export CROSS_COMPILE=arm-none-linux-eabi-
make cm_t3730_defconfig
make menuconfig
make && make uImage && \
INSTALL_MOD_PATH=/home/development/cm-t3730/rootfs make modules_install
In the example above, the Linux kernel image (uImage) will be created in /home/development/cm-t3730/kernel/linux-cm-t3730/arch/arm/boot, and the loadable kernel modules will be installed into the /home/development/cm-t3730/rootfs/lib/modules directory.
When the CM-T3730 is booted with the kernel image created as described above and with networked root filesystem at /home/development/cm-t3730/rootfs/, the system will be able to load the kernel modules properly, thus avoiding module version problems.
