Android Porting

This page describes various effort to port Android to new boards and new processors

Porting Overview
This overview of porting steps was seen on the android-porting list: See http://www.mail-archive.com/android-porting@googlegroups.com/msg06721.html

This glosses over all the kernel work for a new board, and the android-specific kernel patches, but has some good discussion about the flash partitioning and file system bringup process.

If the linux kernel is up and running with all drivers in. (particularly touchscreen and display) it shouldn't be too bad.

IHMO, the easiest way to get you running is to aggregate the initial ramfs built into the kernel with the Android build, the root Android root filesystem (system), and the user data section (mounted as /data I believe) into one root filesystem.

You can then take that root filesystem as one tarball.

Modify the NAND partitioning of the kernel to set aside space for the whole Android rootfs, and of course rebuild the kernel. (Be sure yaffs support is in the kernel) Also no need for a ramfs at this point, just have the kernel look to mtd2 for it's root filesystem, which will be jffs2

Create yourself a busybox root filesystem too. Make that into a jffs2 image.

So your partitioning would look something similar to this (you'll have to decide on the sizes of course): mtd0: bootloader mtd1: kernel mtd2: rootfs (jffs2) mtd3: Android rootfs.

Erase everything on the NAND. Burn the normal Chumby bootloader to mtd0. Burn the the new kernel into mtd1. Burn the jffs2 rootfs image to mtd2.

Boot the device. Hopefully you get yourself to a prompt.

Once you have that prompt mount mtd3 to /mnt/android as a yaffs2 partition. Untar your Android rootfs into /mnt/android. Chown and chgrp everything under /mnt/android to "root" chroot to that mount point "chroot /mnt/android /init"

At this point you should see Android trying to run.

I know that's a bit to chomp on, but it's more of an outline of what you will need to do. Of course it's assuming you have the ability to erase the whole nand and put down images amongst other assumptions, but it should help get your mind around a little bit of the requirements to get Android running on your device.

Regarding your bootloader question, I'd just stick with the current one. You'll only need to modify that if/when you go into having everything compatible with the recovery system. Which is a completely different discussion.

Porting Tutorials

 * Porting Android to a new Device - excellent and thorough paper on porting Android to the Nokia N810.
 * Has a detailed list of kernel changes and annotated diffs.
 * http://wiki.kldp.org/wiki.php/AndroidPortingOnRealTarget
 * Android on OMAP - excellent tutorial covering lots of different issues for porting Android to platforms based on the TI OMAP (ARM) processor
 * Some cursory notes on a port to a PXA board are at: http://letsgoustc.spaces.live.com/blog/cns!89AD27DFB5E249BA!320.entry
 * Adding a new device or changing the configuration of an existing device Android Device

Porting Issues

 * Matt Porter (Mentor Graphics) gave a presentation on difficulties encountered while they were porting Android to MIPS and PPC processors at ELC Europe 2009. His talk was called "Mythbusters: Android" and has lots of good information.
 * See [[Media:Mythbusters_Android.pdf|Mythbusters_Android.pdf]]


 * Dalvik porting guide


 * Matthias Brugger presented his personal "war story" on porting Android at ELC Europe 2012. See his slides on slideshare.

Android Hardware Abstraction Layer
Android talks to standard devices through its hardware abstraction layer, which overlays the kernel interfaces to devices (e.g. devices nodes, Linux system calls, etc.). To add support for your own hardware, or, in particular, to add support to Android for some new type of hardware, you need to understand this abstraction layer. Karim Yaghmour has a good blog entry describing the Android HAL layer: http://www.opersys.com/blog/extending-android-hal

Porting to New Processors

 * Mentor Graphics has ported Android to MIPS and PPC
 * Power.Org supported the work to port Android to PPC
 * Nina Wilner talked about this work, and gave a demo at ELC Europe 2009
 * see [[Media:Android_On_Power.pdf|Android_On_Power.pdf]]

Virtualization environments
There are available some virtualization environments, which allow Android applications (or the whole system) to run on other Linux-based systems, such as MeeGo or Ubuntu.

Here is some information about different systems known to exist:
 * OpenMobile ACL (Application Compatibility Layer)
 * LinuxDevices article: http://www.linuxfordevices.com/c/a/News/OpenMobile-ACL-for-MeeGo/?kc=LNXDEVNL092811
 * OpenMobile product page:http://openmobile.co/products.php
 * Myriad Alien Dalvik
 * LinuxDevices article: http://www.linuxfordevices.com/c/a/News/Myriad-Group-Myriad-Alien-Dalvik/
 * Myried Group page: http://www.myriadgroup.com/Device-Manufacturers/Android-solutions/~/media/D42B513FB5114FF2B4CA13A2D8CE313E.ashx
 * [FIXTHIS - should add tetsuyuki presentation about running Android on Ubuntu here]