This guide applies to

• Raspberry Pi 4
• Android 11 in Tablet mode

Establish build environment :

Ubuntu 18.04.5 LTS (Bionic Beaver) is the recommended build environment, more details read through the AOSP guide https://source.android.com/setup/build/initializing

Required build tools :

• sudo apt-get install git-core gnupg flex bison build-essential zip curl zlib1g-dev gcc-multilib g++-multilib libc6-dev-i386 lib32ncurses5-dev x11proto-core-dev libx11-dev lib32z1-dev libgl1-mesa-dev libxml2-utils xsltproc unzip fontconfig kpartx python-mako
• git config --global user.name "Your Name"
• git config --global user.email "you@example.com"

Installing Repo tool :

Repo tool is required to sync AOSP source code, more details https://source.android.com/setup/develop/repo

• cd HOME_DIR
• mkdir ~/bin
• PATH=~/bin:$PATH
• curl https://storage.googleapis.com/git-repo-downloads/repo > ~/bin/repo
• chmod a+x ~/bin/repo

Sync AOSP source code with Raspberry Pi 4 device tree :

Syncing Android 11 source code, more details https://github.com/android-rpi/local_manifests

• mkdir WORKING_DIRECTORY
• cd WORKING_DIRECTORY
• repo init -u https://android.googlesource.com/platform/manifest -b android-11.0.0_r27
• git clone https://github.com/android-rpi/local_manifests .repo/local_manifests -b arpi-11
• repo sync -j4

(Optional) if network error :

More rarely, Linux clients experience connectivity issues, getting stuck in the middle of downloads (typically during receiving objects). It's been reported that tweaking the settings of the TCP/IP stack and using non-parallel commands can improve the situation. You need root access to modify the TCP setting:

• sudo sysctl -w net.ipv4.tcp_window_scaling=0
• repo sync -j1

Patch framework source

Now that we have the source code synced, we need to modify a few things for it to properly work with a Raspberry Pi 4

• Apply arpi-11 patch
• Change to modify keyboard layout to include power menu, edit key 63 F5 to key 63 POWER at /device/arpi/rpi4/Generic.kl

Patch boot from USB instead of SdCard

Default boot mode is via SD card but for better performance if you want to boot from a USB drive(SSD/Pendrive 3.0 etc), change the boot mode to USB. Modify the file at /device/arpi/rpi4/fstab.rpi4

• edit /dev/block/mmcblk0p2 to /dev/block/sda2
• edit /dev/block/mmcblk0p3 to /dev/block/sda3
• edit /dev/block/mmcblk0p4 to /dev/block/sda4

Build Raspberry Pi 4 Kernel

This build uses the kernel from arpi-5.4.y branch

• If not already installed, make sure to install kernel build tools sudo apt install gcc-aarch64-linux-gnu libssl-dev
• cd /kernel/arpi
• ARCH=arm64 scripts/kconfig/merge_config.sh arch/arm64/configs/bcm2711_defconfig kernel/configs/android-base.config kernel/configs/android-recommended.config
• ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make Image.gz
• ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- DTC_FLAGS="-@" make broadcom/bcm2711-rpi-4-b.dtb
• ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- DTC_FLAGS="-@" make overlays/vc4-kms-v3d-pi4.dtbo

Build AOSP source

Now that we have everything ready, let's build Android 10 image for Raspberry Pi 4. Usually it takes a couple of hours for the build to complete depending on the speed of your machine. For more details read AOSP build instructions http://source.android.com/source/building.html

• cd WORKING_DIRECTORY
• source build/envsetup.sh
• lunch rpi4-eng
• make ramdisk systemimage vendorimage
• (Or a single command : source build/envsetup.sh && lunch rpi4-eng && make ramdisk systemimage vendorimage)

If build host machine has a good number of CPU cores, use -j[n] option with make to increase the build speed, example use 4 cpu core:

• make -j4 ramdisk systemimage vendorimage

Build errors?

(Only if machine is 8GB RAM or less, allocate atleast 6GB to jvm else chances of running into build error

• If error is Exception in thread "main" java.lang.OutOfMemoryError: Java heap space use export _JAVA_OPTIONS="-Xmx8g"
• If error is Picked up _JAVA_OPTIONS: -Xmx8g Killed use -j1

Create Android 11 Image

• cd device/arpi/rpi4
• sudo ./mkimg.sh

Note: Depending on system.img size, change system partition size mkimg.sh

Flash Image to SD Card or USB pendrive or SSD

• balena Etcher https://www.balena.io/etcher/
• Raspberry Pi Imager https://www.raspberrypi.org/downloads