This guide applies to

• Raspberry Pi 4
• Android 10 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 "[email protected]"

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 10 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-10.0.0_r41
• git clone https://github.com/android-rpi/local_manifests .repo/local_manifests -b arpi-10
• repo sync

Addr pi4_tablet device:

• git clone https://github.com/lornova/device_arpi_rpi4_tablet.git device/arpi/rpi4_tablet

(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

• Skip first patch as it's not required in a tablet mode
• Apply second bluetooth patch
• Apply third software video decoder patch
• Apply fourth patch to modify keyboard layout to include power menu, edit key 63 F5 to key 63 POWER at /device/arpi/rpi4/Generic.kl

Build Raspberry Pi 4 Kernel

This build uses the kernel from arpi-5.4.59 branch

• If not already installed, make sure to install kernel build tools sudo apt install gcc-arm-linux-gnueabihf libssl-dev
• cd /kernel/arpi
• ARCH=arm scripts/kconfig/merge_config.sh arch/arm/configs/bcm2711_defconfig kernel/configs/android-base.config kernel/configs/android-recommended.config
• ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- make zImage
• ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- make dtbs

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_tablet-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 10 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

Prepare sd card

Partitions of the card should be set-up like followings.

• p1 128MB for boot : Do fdisk, set W95 FAT32(LBA) & Bootable type, mkfs.vfat
• p2 768MB for /system : Do fdisk, new primary partition
• p3 128MB for /vendor : Do fdisk, new primary partition
• p4 remainings for /data : Do fdisk, mkfs.ext4
• Set volume label of /data partition as userdata: use -L option for mkfs.ext4, and -n option for mkfs.vfat

Write system & vendor partition

• cd out/target/product/rpi4
• sudo dd if=system.img of=/dev/<p2> bs=1M
• sudo dd if=vendor.img of=/dev/<p3> bs=1M

Copy kernel and ramdisk to BOOT partition

• device/arpi/rpi4/boot/* to p1:/
• kernel/arpi/arch/arm/boot/zImage to p1:/
• kernel/arpi/arch/arm/boot/dts/bcm2711-rpi-4-b.dtb to p1:/
• kernel/arpi/arch/arm/boot/dts/overlays/vc4-kms-v3d-pi4.dtbo to p1:/overlays/
• out/target/product/rpi4/ramdisk.img to p1:/