Getting started XDAndroid development

This is a page written for programmers who are interested on developing for XDAndroid, but have no embedded Linux or Android knowledge. It should help you getting started on producing code and fixing bugs in no time.

Supported devices

XDAndroid supports a series of HTC phones based on Qualcomm MSM chipset. Those are the HTC Raphael/Diamond, Topaz, Rhodium, and Blackstone. To find exactly what is your device, open it, remove the battery and look for a model line. For example, the HTC Touch Pro 2 will have this line :

    HTC Touch Pro2 T7373 RHOD100 5VDC = 1A Made in Taiwan
    

It means the device should be identified as RHOD100. Codes vary, such as RHOD400, RHOD500. You have to know your device code in order to properly identify your device for other people and also to find the right configuration/documentation regarding your device's specific hardware.

Check the Supported Devices for more info.

Exploring XDAndroid

These are the parts that make XDAndroid. We will explore each of these topics.

• The HaRET boot loader
• Initrd
• rootfs
• Modified Linux Kernel for the MSM Chipset
  • A set of add-on Kernel Modules, that can be called by applications
• A modified Android build
  • A set of proprietary Google/HTC software taken from other sources.

HaRET boot loader

Currently XDAndroid boots from Windows CE. Haret is used as a boot loader. On Windows CE, you should place the Kernel (zImage file), the initrd (initrd.gz file), the special boot parameters (startup.txt file) and HaRET (haret.exe) on the sd card filesystem, in the same directory (usually /andboot), and then run HaRET.exe. The startup.txt file must be changed to pass kernel specific information that will enable/configure your device correctly. The XDAndroidStartup program for Windows Mobile can correctly set the startup.txt file, given your device id code.

Here is the boot sequence for Android :

1. HaRET starts, and reads the startup.txt file - startup.txt informs the location of kernel, initrd and boot parameters
2. HaRET loads the kernel and the initrd to the memory
3. HaRET boots the kernel passing along the parameters
4. The Kernel mounts the initrd disk on a memory filesystem
5. Initrd does ???
6.  ???
7. Initrd loads the rootfs from the sdcard, mounts it, ans sets it as the new root filesystem
8.  ???
9. sistem.ext2
10.  ????
11. Android Starts

Initrd

If you don't know what is a initrd and its relation the the kernel, you should read the official Kernel.org initrd documentation. On XDAndroid, the initrd :

• Prepares the system for the rootfs to be mounted (TODO: Explain what is "prepare the system")
• Mounts the a new root file system using the rootfs image.
• TODO: List any other initrd functions

rootfs

• responsible for the key maps
• TODO: list other features for rootfs

Qualcomm-S-MSM Linux Kernel

The kernel used by Xdandroid is located at gitorious linux-on-qualcomm-s-msm repo. This Kernel is branched from the google's android kernel, modified to support Qualcom specific hardware. The kernel is responsible for (almost) all the hardware support, including display, camera, wifi, audio, power management, etc. With a proper kernel, even a generic build of Android using the vanilla source code from google should bring up the phone.

Add-on Kernel Modules

A modules-2.6.xxxxxxxx.tar.gz file will most times be packed with the kernel. Those represent some kernel modules that weren't integraded on the kernel either because they are closed source, either because they are hard to integrate, either because they are not used. The wifi kernel module resides on this package, and it is later on loaded and used via the libhardware_legacy on userland. The Netfilter module, with is also not used, will also go into this diretory.

Modified Android Build

Android is composed of multiple software sources that together make up the whole system. Xdandroid uses the official google android repository (git://android.git.kernel.org/) and it's own gittorious repository. To manage the commits/syncs at the same base on different repositories, Android and XDAndroid use a google tool to work with multiple git repositories called Repo.

TODO: Understand how .repo/manifest.xml file really works

The Android build system

On Android, in order to make a port for a specific device, you have to build a Product tree directory and define a product type. Then you have to make a buildspec.mk, containing the new product you have defined on the PRODUCT_TYPE parameter. Then you call the Android build system, and it will automagically create a build for your product on the //out directory. So next we learn more about the Product tree.

The XDAndroid Product Tree

Is located at //device/xandroid/msm. It serves both as an android board folder (has definition for boards) and as an android products folder ( has definition for products). This is what we find in our company folder :

• Board Config Files :
  • AndroidBoard.mk ( board makefile, defines settings for all products using this board)
  • BoardConfig.mk ( compile-time definitions. TODO : Find out the difference between this file and AndroidBoard.mk)
• Product Definition Files :
  • AndroidProducts.mk ( list of all products makefiles in this product folder)
  • generic_msm.mk ( another root product define - could be used to make a clean default build)
  • full_msm.mk ( the main root product define file)
    • device_msm.mk ( gets inherited by full_msm.mk )
    • device_msm_us/as/eu.mk ( gets inherited by full_msm.mk )
• Files that will just get copied to the final build
  • Overlay - Directory (resources that replace Android original resource files - copied with overlay definition)
  • bootanimation.zip (nice XDA boot animation - to /system/media)
  • apns-conf.xml (complete list of worldwide data connection info. to /system/etc)
  • media_profiles.xml ( configuration for media/video/music features. to /system/etc)
  • egl.cfg ( open gl configuration. This should probably go to /system/lib/egl TODO: FIND WHO COPIES IT)
  • h2w_headset.kl ( key maps for the USB headset. TODO: find out who copies this)
  • vold.fstab (android fstab, defines that our sdcard should be mounted at /sdcard)
  • wlan.ko ( binary, will probably get copied to somewhere TODO : FIND OUT WHO COPIES IT)
  • init.xdandroid.rc ( android-init-language init file. TODO: find who copies this)
• Helper Scripts
  • Tools - Directory ( Set of helper scripts)
    • generate_release_image.sh --- ???
    • release_manifest.sh --- ???
  • unzip-files.sh ( extracts all proprietary software (gapps, hw3d, etc) into a //vendor directory)
  • setup-makefiles.sh (seens to be related to including proprietary code in TODO : FIND OUT THAT THIS IS )
• Other files evaluated by Android Build System
  • vendorsetup.sh ( called by build/envsetup.sh - adds a lunch option TODO: FIND OUT WHY WE NEED THIS)
  • system.prop (modify system properties - pixel density, etc)
• Empty or all-commented files
  • CleanSpec.mk (comented-out file, in future could be used to define clean-steps for the build system)
  • froyo.build ( Empty file ??? TODO: find out why it exists)
  • kernel ( Empty file ??? TODO: find out why it exists)

Board Config Files

BoardConfig.mk

Defines TARGET_BOARD_PLATFORM, TARGET_CPU_ABI, TARGET_ARCH_VARIANT according to our hardware. Since we are using Haret, it sets TARGET_NO_BOOTLOADER. Also sets WITH_JIT and ENABLE_JSC_JIT to use a faster JIT compiler. Sets Wifi, Bluetooth, the size for the generated image files, disables OpenGLES-2 ( our hardware doesn't support it)

Also

• TARGET_BOOTLOADER_BOARD_NAME := msm ???
• BOARD_KERNEL_CMDLINE := no_console_suspend=1 ???
• USE_PV_WINDOWS_MEDIA := false ???
• BUILD_WITH_FULL_STAGEFRIGHT := true ???

AndroidBoard.mk

Probably the equivalent to Android.mk

Sets the path for our pre-built kernel,

--- ?????? -----

file := $(TARGET_OUT_KEYLAYOUT)/h2w_headset.kl ALL_PREBUILT += $(file) $(file) : $(LOCAL_PATH)/h2w_headset.kl | $(ACP) $(transform-prebuilt-to-target)

file := $(TARGET_ROOT_OUT)/init.xdandroid.rc ALL_PREBUILT += $(file) $(file) : $(LOCAL_PATH)/init.xdandroid.rc | $(ACP) $(transform-prebuilt-to-target)

--- ?????? ----- Includes AndroidBoardVendor.mk - that does a BOARD_GPS_LIBRARIES := librpc and disables CAMERA

Product Definition Files

These are the full_msm.mk, device_msm.mk, device_msm_us/as/eu.mk.

• They inherit from languages_full.mk, making the final build have a full list of languages
• They inherit from full.mk, making our build a "complete" one.
• They inherit from device/common/gps/gps_us_supl.mk
• They inherit from vendor/xdandroid/msm/device_msm_us-vendor.mk
• They inherit from vendor/xdandroid/msm/device_msm-vendor.mk

• They define PRODUCT_NAME, PRODUCT_DEVICE, PRODUCT_MODEL, PRODUCT_MANUFACTURER with our string settings
• They define DEVICE_PACKAGE_OVERLAYS with our overlay folder
• They define PRODUCT_LOCALES to support hdpi screen density
• They define PRODUCT_PACKAGES [Gallery,PinyinIME, OpenWnn, libWnnEngDic, libWnnJpnDic, libwnndict]
• They define PRODUCT_PROPERTY_OVERRIDES, to set the supported opengles version (ro.opengles.version=65536)

• They copy frameworks/base/data/etc/ [core_hardware, camera.autofocus, telephony.gsm, location.gps, wifi] to system/etc/permissions/
• They copy media_profiles.xml and apns-conf.xml to /system/etc
• They copy bootanimation.zip to and apns-conf.xml to /system/media

system.prop

Sets the LCD pixel density, the default network type (WCDMA ???) and rild.libpath=/lib/froyo/libhtcgeneric-ril.so ???

For convinience, on XDAndroid, the root makefile ( originally at //core/root.mk) was copied to //Makefile. So, to call Android's build system, you call make on the root folder. The build system will load the buildspec.mk file, and create a build based on the parameters on that file, specially the TARGET_PRODUCT parameter. The build system creates the buid on out/product/msm .

 . build/envsetup.sh -- ???

====Empty or all-commented file

References

Android.com Plataform developer guide Guide showing how to make a path to the official android repo