1. Porting Android to Beagleboard
Anish Dhanekula
Karl Arndt

2. Porting Android to Beagleboard
What is Android?
Linux-based Operating System for Mobile Devices
Developed by Android, Inc.
Acquired by Google
Open-Source, under Apache License
Proprietary extensions developed by vendors don’t have to be submitted back to open-source commnunity
Porting Android to Beagleboard

3. Porting Android to Beagleboard
What is Android?
Modified Linux Kernel
Éclair (Android v2.0/2.1) based on
Filesystem
Uses the Bionic C Library instead of glibc
Dalvik Java Virtual Machine
Is it really Linux?
Sort of… Definitely Linux kernel, but not a traditional userspace
Porting Android to Beagleboard

4. Porting Android to Beagleboard
What is Android?
Porting Android to Beagleboard

5. Porting Android to Beagleboard
What’s a Beagleboard?
Porting Android to Beagleboard

6. Porting Android to Beagleboard
What’s a Beagleboard?
OMAP 3530
TI SoC with ARM Cortex A8 and 64x DSP
SDRAM and Flash on-package with Package-on-Package (PoP)
Porting Android to Beagleboard

7. Porting Android to Beagleboard
What’s a Beagleboard?
Peripherals
SD/MMC Socket for Storage
DVI-D and S-Video
Stereo In and Out
USB
Serial
Bootloader
U-Boot comes loaded on the PoP Flash
Porting Android to Beagleboard

8. Porting Android to Beagleboard
Porting Process
Get Android Source
Kernel and Filesystem
Prove it can work
Modify Kernel files as necessary to work with Beagleboard
Compile
Write to SD Card
Try to Boot
Doesn’t work – pray that your Beagleboard gets stolen while you grab dinner
Fix Kernel Boot Errors
Repeat
Porting Android to Beagleboard

9. ‘Git’ing Android Source
Kernel – android.git.kernel.org
OMAP tree
Filesystem – source.android.com
We used a prebuilt filesystem known to work on Beagleboard in order to focus on the kernel
Git
Source management tool
Porting Android to Beagleboard

10. Porting Android to Beagleboard
Storage Format
Kernel and Filesystem need to be stored in a particular way on the SD Flash
Two Partitions
FAT32 Boot Partition
Holds U-Boot update and compressed Kernel Image (uImage)
EXT3 Filesystem Partition
Holds the complete root filesystem
Porting Android to Beagleboard

11. Porting Android to Beagleboard
Early Boot Process
OMAP PoP Flash comes with U-Boot, but needs to be replaced on boot
The PoP Flash U-Boot knows to attempt to boot from the SD Flash first, and when it does it finds the updated U-Boot
Environment variables must be set to boot properly
setenv bootcmd ‘mmc init; fatload mmc uImage; bootm ’
setenv bootargs 'mem=128M androidboot.console=ttyS2 console=tty0 console=ttyS2,115200n8 root=/dev/mmcblk0p2 rw init=/init
Porting Android to Beagleboard

12. Porting Android to Beagleboard
Prove it can Work
Rowboat
Someone has already ported Android to Beagleboard
Confirmed that this distribution works on our board
Porting Android to Beagleboard

13. Porting Android to Beagleboard
Compiling the Kernel
Since the kernel is being compiled on an x86 host for an ARM target, cross-compiling is necessary
The arm-eabi toolchain is used for this
Included in the Android Filesystem Source
make ARCH=arm CROSS_COMPILE=/prebuilt/linux-x86/toolchain/arm-eabi-4.4.0/bin/arm-eabi uImage –j4
uImage is the compressed Kernel Image
-j4 tells Make it can use 4 threads (two per CPU on a dual-core machine
Porting Android to Beagleboard

14. Modifying Kernel Source
Create the .config file
make defconfig
make ARCH=arm defconfig
make ARCH=arm omap3_beagle_defconfig
Edit .config to include all necessary settings and modules
make ARCH=arm menuconfig
Porting Android to Beagleboard

15. Modifying Kernel Source
menuconfig
Porting Android to Beagleboard

16. Modifying Kernel Source
.config
Compilation parameters are chosen
Particular implementation of an architecture
Drivers are chosen
Must determine the correct drivers for your SoC/Board and include them here
Drivers can be included as built-in or modular
Porting Android to Beagleboard

17. Modifying Kernel Source
.config – selecting the right drivers
Real Time Clock
Real Time Clock initialization was failing on kernel boot
Found that the Beagle uses a TWL4030 I2C RTC Controller
Had to enable I2C, TWL Core, and TWL4030 Drivers
Porting Android to Beagleboard

18. Modifying Kernel Source
.config – selecting the right drivers
MMC/SD
Filesystem is stored on SD card
Found correct driver by sorting through Angstrom Linux running on the Beagleboard
Porting Android to Beagleboard

19. Modifying Kernel Source
Correct Drivers are chosen, but Kernel won’t boot…
Need to dig into actual Kernel Source and Boot Process
Porting Android to Beagleboard

20. Modifying Kernel Source
Kernel Boot Process
Run code from /arch/arm/mach-omap2 to initialize devices
Run /init/main.c to mount the root filesystem
Once the root filesystem is mounted, run /init (or whatever is specified to U-Boot) as the first process
Porting Android to Beagleboard

21. Modifying Kernel Source
RTC is initialized now, but Kernel Boot still hangs
“Waiting for root device /dev/mmcblk0p2…”
This message was found in /init/do_mounts.c
Called in /init/main.c
While loop continuously polling
Device_probe_done()
name_to_dev_t()
Porting Android to Beagleboard

22. Modifying Kernel Source
One of the routines is not completing
Traversed name_to_dev_t() with printk
Seems to work fine
Difficult to traverse name_to_dev_t()
Decided to look through initial device initialization code in /arch/arm/mach-omap2 and SD driver in /drivers/mmc/host/omap_hsmmc.c
Porting Android to Beagleboard

23. Modifying Kernel Source
/arch/arm/mach-omap2/board-omap3beagle
Several __init statements
omap3_beagle_init
Calls omap3beagle_flash_init
This is where the devices are initialized during bootup, but we can’t find anything wrong…
Porting Android to Beagleboard

24. Porting Android to Beagleboard
Next Steps
Hard-coded device names
Porting Android to Beagleboard

25. Things we would do differently
Spend less time modifying the .config file and more time on the kernel source itself
Maybe try Network File System (NFS) to store the Filesystem
Porting Android to Beagleboard

26. Porting Android to Beagleboard
References
Linux Kernel in a Nutshell
Greg Kroah-Hartman
Linux from Scratch
Gerard Beekmans
code.google.com/p/beagleboard/wiki
code.google.com/p/rowboat/wiki
source.android.com
android.git.kernel.org
Porting Android to Beagleboard

27. Porting Android to Beagleboard
Questions?
Porting Android to Beagleboard