This document provides an overview of porting Android to new platforms. It discusses the Android software stack, the Android Open Source Project structure, the AOSP code structure, common Android hardware abstraction layers, device configuration files, the AOSP build process, the Android boot process, and Android debugging tools.

1. Porting Android to new Platforms
Amit Pundir
Android Engineer, Linaro

2. Android Software Stack

3. Applications
Application
Frameworks
Libraries &
Runtime
Linux
Kernel Audio Display
Hardware
Abstraction
Layers
Firmware Binaries
WiFi BinderCamera Logger ...
GPSRadio (RIL)Camera
Media
NFSSensorsAudio ...
Skia
Core Libraries
Dalvik VM...
SQlite
ALSA
Freetype
Input
Webkit
System Services
Power Manager Activity Manager Package Manager
Content Manager Battery Service Window Manager
Location Manager Audio Service Alarm Manager
Network Manager Media Server ...
Home SettingsMedia PlayerCameraDialer ...

4. Android Open Source Project

5. ● AOSP is not a single project.
● Hundreds of independent projects having own Git repositories.
● Don't need to pull the projects one by one. Repo tool for the
rescue.
● AOSP manifest file to download a snapshot.
● Android Documentation: Downloading the source tree
http://source.android.com/source/downloading.html

6. AOSP Code Structure

7. bionic Android's C library.
bootable Legacy Bootloader/Recovery code for reference
build AOSP Build framework
cts Android's Compatibility Test Suit
dalvik Dalvik Virtual Machine
development Development tools #tutorials #monkey
device Vendor specific configuration files
external External projects used in AOSP
frameworks Android core application framework
hardware Hardware specific libraries/modules #HAL
kernel Linux Kernel
libcore Apache Harmony. Fee Java implementation. Used by
Dalvik.
ndk Native Development Kit
packages AOSP's stock applications
prebuilt Prebuilt binaries such as Toolchain
sdk Android's Software Development Kit
system Android's core system libraries/binaries #init #toolbox #adb

8. Android Kernel

9. ● Android patches are not available mainline.
● android-common project
→ Android patches on top of Linus's base tree.
● Extract patches and apply them to your Target specific
kernel.

10. Android Kernel Features

11. ● Binder
→ Android's IPC mechanism. Inspired from Open Binder project.
● Ashmem or Anonymous Shared Memory
→ Shared memory allocator. Discards shared units under memory pressure.
● Logger
→ Android's driver which logs data from user space.
● Wakelocks
→ Prevents a system to enter suspend or low power states.
● Out Of Memory handler
→ Aggressive OOM handler. Triggers before Kernel's default
implementation.
● Alarm
→ Android's alarm timer implementation on top of Kernel's RTC
implementation.
● RAM console
→ Logs last Kernel log. Accessible through /proc/last_kmsg
● Paranoid network
→ Network administration through uid/pid e.g AID_NET_*

12. Common Android Hardware
Abstraction Layers

13. libaudio.so AudioHardwareInterface implementation.
libgralloc.so Graphics Buffer Allocator
“hardware/libhardware/modules/gralloc/”
libsensor.so Sensor modules.
libcamera.so CameraHardwareInterface implementation.
libgps.so GPS module.
libstagefrighthw.so Stagefright implementation for h/w codecs.
libril.so Radio interface layer module
... ...

14. HAL Module/Library loaders

15. ● Run time loading
● hw_get_module()
● libgps, liblights, libgralloc, libsensors,
liboverlays etc
● dlopen()
● libstagefrighthw, libril etc
● Build time linking
● libaudio, libcamera etc
● Linux standard sysfs and /dev nodes
● Power management, Input devices etc

16. Device/Vendor specific
configuration files

17. ● Build config files
● Target build requirements are set by build/core/{main.mk,
config.mk, product.mk, product_config.mk}
● Build process looks for target specific config file
BoardConfig.mk at device/*/$(TARGET_DEVICE) or vendor/*/$
(TARGET_DEVICE)
● TARGET_PRODUCT = TARGET_DEVICE =
PRODUCT_DEVICE, where PRODUCT_DEVICE is defined in
AndroidProducts.mk
● Android Run time config files init.rc, init.TARGET_PRODUCT.rc,
ueventd.rc, ueventd.TARGET_PRODUCT.rc, vold.fstab etc
● Set optional PRODUCT_PACKAGES for Pre-loaded applications.
● Generate Project manifest file. It is different from an Android
Application Manifest file.

18. AOSP Build Process

19. ● Android Documentation: Building the system
http://source.android.com/source/building.html
● $ . build/envsetup.sh
→ Setting up build environment
● $ lunch
→ Choose correct TARGET_PRODUCT
● $ export USE_CCACHE = 1
→ will cache object files generated by the C/C++ compiler which can
be used to speed up next build.
● $ make -jX
→ where X = “the number of CPU cores in your build machine” + 1.
OR
● $ mm
→ make alias which is handy while building AOSP projects
independently.

20. Android Boot Process

21. Kernel
Init
Service
Manager
system
server
Zygote... ...
binder
System Services
Activity Manager Power Manager Package Manager
Content Manager Battery Service Window Manager
Location Manager Audio Service Alarm Manager
Network Manager Media Server ...
System
Server
Android
Application

22. Android Debugging

23. ● Increase loglevel in init.rc
● dmesg
→ Dump Kernel logs
● logcat
→ Dump System logs
● adb and ddms
→ Android debug bridge and tool for remote debugging.
● dumpsys and dumpstate
→ Dump system services meminfo
● /proc/last_kmsg
→ Last dmesg or kernel log to debug random crashes.
● Traceview ?
→ http://android-developers.blogspot.com/2010/10/traceview-
war-story.html

24. Thank You