CM-T335: Android: Kernel
Contents
Overview
Linux kernel supplied with the CM-T335 Android Demo package provides support for the on-board peripherals and abstracts the functionality provided by the hardware. Current support coverage is specified on the 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-T335 modules. The kernel binary is optimized for using with Android, however can be used with any Linux ARM compatible distribution as well.
Building kernel for CM-T335
In this article we assume that the /home/development/cm-t335/android directory is used for CM-T335 kernel development.
Getting cross-compiler
The recommended pre-built toolchain repository is hosted on the Rowboat Gitorious website.
- Clone the toolchain repository. By default it will be created in the directory named prebuilts-gcc-linux-x86-arm-arm-eabi-4_6/.
cd /home/development/cm-t335/android git clone -b rowboat-jb git://gitorious.org/rowboat/prebuilts-gcc-linux-x86-arm-arm-eabi-4_6.git
Getting kernel sources
The Rowboat Kernel sources repository is hosted on the Rowboat Gitorious website.
- Clone the kernel sources repository. By default it will be created in the directory named kernel/.
cd /home/development/cm-t335/android git clone git://gitorious.org/rowboat/kernel.git
- Create a branch for CM-T335 development. The CM-T335 patches are generated vs. rowboat-jb-am335x-4.1.2 tag (996686459db1181a5deaf5d493681ecb5bf43ad7 commit) in the Rowboat kernel tree. It is recommended to use exactly the same baseline to avoid merge conflicts:
git checkout -b cm-t335-dev rowboat-jb-am335x-4.1.2
- Apply the CM-T335 patch:
cd /home/development/cm-t335/android/kernel git apply /path/to/cm-t335-android/kernel/linux-3.2.0-cm-t335-1.patch
Building the kernel
- Setup the toolchain
export PATH=/patch/to/cross/compiler/prebuilts/gcc/linux-x86/arm/arm-eabi-4.6:$PATH export ARCH=arm export CROSS_COMPILE=arm-eabi-
- Build the kernel
cd /home/development/cm-t335/android/kernel make cm_t335_android_defconfig make menuconfig make uImage
In the example above, the Linux kernel image (uImage) will be created in /home/development/cm-t335/android/kernel/arch/arm/boot directory.
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There is no need to build and install any kernel modules into the Android Demo image for CM-T335, as all the kernel driver modules are compiled in the kernel binary. |
Basic platform support
The CM-T335 basic platform support is implemented in the arch/arm/mach-omap2/board-cm-t335.c file of Linux kernel source tree. This file includes default setup of multi-functional pins, registration of the devices integrated in the CM-T335 module and definitions of platform-specific configuration for these devices.
USB Gadget
The CM-T335 Android Demo image supports both USB host and USB device ports.
USB host can be used to connect Keyboard/Mouse, Mass storage device, etc.
The USB device port is used for connecting to a PC workstation.
To enable/disable USB Gadget support in the kernel configuration menu choose Device Drivers--->USB support--->USB Gadget Support submenu.
Then enable/disable USB Gadget Drivers:
┌───────────────────────────── USB Gadget Support ──────────────────────────────┐ │ Arrow keys navigate the menu. <Enter> selects submenus --->. Highlighted │ │ letters are hotkeys. Pressing <Y> includes, <N> excludes, <M> modularizes │ │ features. Press <Esc><Esc> to exit, <?> for Help, </> for Search. Legend: │ │ [*] built-in [ ] excluded <M> module < > module capable │ │ ┌───────────────────────────────────────────────────────────────────────────┐ │ │ │ --- USB Gadget Support │ │ │ │ [ ] Debugging messages (DEVELOPMENT) │ │ │ │ [ ] Debugging information files (DEVELOPMENT) │ │ │ │ [ ] Debugging information files in debugfs (DEVELOPMENT) │ │ │ │ (2) Maximum VBUS Power usage (2-500 mA) │ │ │ │ (2) Number of storage pipeline buffers │ │ │ │ <*> USB Peripheral Controller (Inventra HDRC USB Peripheral (TI, ADI,│ │ │ │ <*> USB Gadget Drivers (Android Gadget) ---> │ │ │ └───────────────────────────────────────────────────────────────────────────┘ │ ├───────────────────────────────────────────────────────────────────────────────┤ │ <Select> < Exit > < Help > │ └───────────────────────────────────────────────────────────────────────────────┘
Finally choose Android Gadget option:
┌──────────────────────── USB Gadget Drivers ────────────────────────┐ │ Use the arrow keys to navigate this window or press the hotkey of │ │ the item you wish to select followed by the <SPACE BAR>. Press │ │ <?> for additional information about this option. │ │ ┌─────────^(-)───────────────────────────────────────────────────┐ │ │ │ ( ) File-backed Storage Gadget (DEPRECATED) │ │ │ │ ( ) Mass Storage Gadget │ │ │ │ ( ) Serial Gadget (with CDC ACM and CDC OBEX support) │ │ │ │ ( ) MIDI Gadget (EXPERIMENTAL) │ │ │ │ ( ) Printer Gadget │ │ │ │ (X) Android Gadget │ │ │ └─────────v(+)───────────────────────────────────────────────────┘ │ ├────────────────────────────────────────────────────────────────────┤ │ <Select> < Help > │ └────────────────────────────────────────────────────────────────────┘
The relevant initialization including the pin-muxing for MMC bus is done in the CM-T335 board file. Please refer to the CM-T335 board file kernel/arch/arm/mach-omap2/board-cm-t335.c for more details.
