Android Raspberry Pi Kernel Build Walkthrough

I've had some queries on the blog about building the Raspberry Pi kernel I hacked together. Here are the instructions on how to compile the Android kernel for the Raspberry Pi environment.

This kernel should work with the headless Android filesystem.

NOTE: Since I have not been able to get my hands on the hardware I haven't tried it myself. You are on your own with this. I doubt it works right out of the box...

Build Instructions

All build instructions reference the base directory where you want to put the source files. For me I used:
export RASP_SRC_BASE=~/work/raspberry-pi

Get the kernel sources for linux-3.1.9

mkdir -p $RASP_SRC_BASE/kernel/patches

cd $RASP_SRC_BASE/kernel
wget http://www.kernel.org/pub/linux/kernel/v3.0/linux-3.1.9.tar.bz2
tar jxvf linux-3.1.9.tar.bz2

Apply the Raspberry Pi patch

cd $RASP_SRC_BASE/kernel/patches/
wget http://www.cnx-software.com/patch/r-pi_linux_3.1.9.patch.gz
gunzip r-pi_linux_3.1.9.patch.gz
cd $RASP_SRC_BASE/kernel/linux-3.1.9
patch -p1 < ../patches/r-pi_linux_3.1.9.patch

Get the Toolchain

cd $RASP_SRC_BASE/toolchain
wget https://sourcery.mentor.com/sgpp/lite/arm/portal/package9728/public/arm-none-linux-gnueabi/arm-2011.09-70-arm-none-linux-gnueabi-i686-pc-linux-gnu.tar.bz2
tar jxvf arm-2011.09-70-arm-none-linux-gnueabi-i686-pc-linux-gnu.tar.bz2 

Set up the environment variables

export PATH=$PATH:$RASP_SRC_BASE/toolchain/arm-2011.09/bin
export CROSS_COMPILE=$RASP_SRC_BASE/toolchain/arm-2011.09/bin/arm-none-linux-gnueabi-
export ARCH=arm
export CCACHE_DIR=~/.ccache/
export USE_CCACHE=1

Make sure the build works

At this point, configure and build the Raspberry Pi kernel.

Configure the kernel

cd $RASP_SRC_BASE/kernel/linux-3.1.9
cp arch/arm/configs/bcmrpi_cutdown_defconfig .config
make oldconfig

Make the kernel

make -k -j6

Apply the Android kernel patch

cd $RASP_SRC_BASE/kernel/patches/
wget https://dl.dropbox.com/u/24888185/android_3.1.9_patch.tar.gz
gunzip android_3.1.9_patch.tar.gz
cd $RASP_SRC_BASE/kernel/linux-3.1.9
patch -p1 < ../patches/linux-3.1.9-stock-to-android.patch
patch -p1 < ../patches/linux-3.1.9-fs-proc-base.patch
patch -p1 < ../patches/linux-3.1.9-yaffs2.patch
patch -p1 < ../patches/linux-3.1.9-power.patch

Build Raspberry Pi Android

You are ready to build the Raspberry Pi Android kernel now.

Configure the kernel

cd $RASP_SRC_BASE/kernel/linux-3.1.9
wget https://dl.dropbox.com/u/24888185/rasp_android_defconfig.gz
gunzip rasp_android_defconfig.gz
mv rasp_android_defconfig .config

Make the kernel

make -k -j6

Headless Android on Raspberry Pi - Progress Report

I know you are all dying to know how my progress has been going on the Raspberry Pi Android port. Well, it's coming along. 

The Raspberry Pi currently uses a 3.1.9 ARM Linux kernel. The version of Android I decided to port over uses the 3.0.8 ARM kernel. To patch the 3.1.9 ARM kernel with Android, I had to go a circuitous route.

It would have been pretty easy if there were patches already out there that were JUST Android patches. I couldn't find any. I'm sure there is a way, using Git, to isolate the Android patches from the Git Android repository, but I haven't spent enough time playing with Git to do it. So, I went the old fashioned way.

To create my own isolated Android patch, I first needed to find an Android running on a 3.x.x version of the kernel. Ice Cream Sandwich is running against a 3.0.8 kernel (at the time I did this post) so that is where I started. The trick was to not include any ARM patches with the isolated Android patch because I needed to keep all of the Raspberry Pi ARM changes in tact.

So, starting with an x86 3.0.8 Android kernel I found, I created a patch from stock x86 3.0.8 to Android x86 3.0.8. That gave me an isolated Android patch. Then I applied that isolated Android patch to the 3.1.9 Raspberry Pi kernel. That took my Raspberry Pi kernel to an Android kernel.

Now I need to make the modifications to the Ice Cream Sandwich Android to make it a Headless Ice Cream Sandwich (in the shape of an Android, of course.)

Note:
Why x86? Well, that's a good question.

In order to get a clean isolated Android patch I needed to start with something that I could:
a) get a good clean stock kernel for, and
b) if there were unnecessary changes to the architecture or driver files they wouldn't affect and ARM system.

I could have attempted an ARM 3.x.x kernel but it's pretty hard to find an ARM kernel (of the 3.x.x revision) with an matching ARM kernel with Android that you would have confidence that the ARM portion is all the same. At least the x86 stuff is fairly well known and consistent.

Stay tuned, more to come!

Mmmmm... Pie..... Raspberry Pi to be exact

Back in January and early February there was a lot of interesting news on Raspberry Pi. Like every other technology enthusiast (read "geek") I have been watching the stories and been interested in that little piece of hardware.

"Why" you may ask? Considering that it has video output but no touch screen has lead most of the developer community to focus on why it can't (or shouldn't) support Android. However, it's perfect for creating a droid army to rival that of the Trade Federation <insert evil laugh here>.

Seriously though, I can't think of anything better than a low cost, easily accessible hardware platform to put a Headless Android on.

One problem... it's all sold out. Bother.

Stay tuned for some activity in the near future on porting the Android patches to the Raspberry Pi kernel, minus of course the video subsystem. Let's see what we get, shall we? Headless Raspberry Pi anyone, with Gingerbread crust? Mmmmmm, sounds good to me!