Android Platform Developer's Guide

Android Platform Developer's Guide
Android Platform Developer's Guide 1
Android Platform Developer's Guide 5
About this Guide 5
Intended Audience 5
Getting Started with Android 5
Android Build System 6
In this document 6
Building the Android Platform 8
Building the Android Kernel 10
Build Variants 11
Configuring a New Product 12
In this document 12
Detailed Instructions 12
New Product File Tree 15
Product Definition Files 15
Build Cookbook 17
In this document 17
Building a simple APK 17
Building a APK that depends on a static .jar file 18
Building a APK that should be signed with the platform key 18
Building a APK that should be signed with a specific vendor key 19
Adding a prebuilt APK 19
Adding a Static Java Library 19
Android.mk Variables 20
Creating Release Keys and Signing Builds 29
In this document 29
Introduction 29
Generating keys 30
Signing a build for release 31
Customization 32
In this document 32
Boot Screen Customization 32
Network Customization Platform 33
Customizing pre-loaded applications 34
Customizing browser bookmarks 35
Email Provider Customization 37
Platform Themes 41
Bring Up 41
1. Confirm a Clean Installation of a Basic Linux Kernel 42
2. Modify Your Kernel Configuration to Accommodate Android Drivers 42
3. Write Drivers 42
4. Burn Images to Flash 43
5. Boot the kernel and mount the RAMdisk. 43
6. Debug Android-specific init programs on RAMdisk 44
7. Verify that applications have started 44
8. Pulling it all together 45
Android Init Language 45
Display Drivers 50
In this document 50
Functionality 51
Implementing Your Own Driver (Driver Template) 52
Troubleshooting 59
Keymaps and Keyboard Input 59
In this document 59
Functionality 60
Key Layout Map 61
Key Character Map 63
Implementing Your Own Driver (Driver Template) 67
Sample Implementation 70
Lights 70
In this document 70
Building a Lights Library 71
Interface 71
Audio 75
In this document 75
Building an Audio Library 77
Interface 77
Building a Camera Library 84
Sequence Diagrams 85
Wake Locks 90
Driver API 92
User-space API 93
Types of Wake Locks 93
Exploring a Wake Lock Example 93
PowerManager class 94
Registering Drivers with the PM Driver 94
Early Suspend 95
Sensors 95
In this document 95
Building a Sensor Library 96
Interface 97
RIL Initialization 99
RIL Interaction 99
Implementing the RIL 102
RIL Functions 103
Dalvik 105
In this document 105
Core Libraries 106
JNI Call Bridge 106
Interpreter 107
Mterp Interpreter Structure 108
Getting Started With Mterp 109
Replacing Stubs 110
Interpreter Switching 111
Testing 112
Testing and Debugging 113
Instrumentation Testing 113
In this document 113
Instrumentation Framework 114
Platform Test Suites 116
Running Tests 116
Writing Tests 120
Debugging with GDB 123
In this document 123
Debugging 124
Just-In-Time Debug Feature 126
Debugging Native Code 127
In this document 127
Capturing logs 127
Debug Scenarios 127
Debugging with tcpdump and other tools 135
Installing tcpdump 135
Running tcpdump 136
Other network debugging commands 138
Android Platform Developer's Guide
Welcome to the Android Platform Dev Guide! This guide provides an under-the-hood introduction to the Android platform, and is designed for platform developers and manufacturers building Android-powered devices.
If you're a software developer interested in developing applications for Android, please visit the Android Developers site.
About this Guide
This guide is divided into sections by logical platform component (see the table of contents on the left). Android is a complex project under constant development, and the level of detail, as well as the rate of change, may vary from section to section. This guide will be updated regularly as more content becomes available.
Intended Audience
This guide is intended for engineers who are proficient with building and running Linux on embedded devices. It aims to provide explanation of the Android platform rather than Linux or embedded development in general.
Getting Started with Android
If you are new to Android, start with the platform documentation on the following sites:
Android Developers site: This site offers high-level platform documentation and architecture concepts.
Android Open Source Project site: This site provides instructions on how to get the source code, establish a development environment, and perform a simple build.
When you are ready to start customizing the platform or porting to your target hardware, start in this guide with the Build System overview.
Android Build System In this document
Android uses a custom build system to generate tools, binaries, and documentation. This document provides an overview of Android's build system and instructions for doing a simple build.
Android's build system is make based and requires a recent version of GNU Make (note that Android uses advanced features of GNU Make that may not yet appear on the GNU Make web site). Before continuing, check your version of make by running % make -v. If you don't have version 3.80 or greater, you need to upgrade your version of make.
Understanding the makefile
A makefile defines how to build a particular application. Makefiles typically include all of the following elements:
Name: Give your build a name (LOCAL_MODULE := ).
Local Variables: Clear local variables with CLEAR_VARS (include $(CLEAR_VARS)).
Files: Determine which files your application depends upon (LOCAL_SRC_FILES := main.c).
Tags: Define tags, as necessary (LOCAL_MODULE_TAGS := eng development).
Libraries: Define whether your application links with other libraries (LOCAL_SHARED_LIBRARIES := cutils).
Template file: Include a template file to define underlining make tools for a particular target (include $(BUILD_EXECUTABLE)).
The following snippet illustrates a typical makefile.
LOCAL_PATH := $(my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE :=
LOCAL_SRC_FILES := main.c
LOCAL_MODULE_TAGS := eng development
LOCAL_SHARED_LIBRARIES := cutils
include $(BUILD_EXECUTABLE)
(HOST_)EXECUTABLE, (HOST_)JAVA_LIBRARY, (HOST_)PREBUILT, (HOST_)SHARED_LIBRARY,
(HOST_)STATIC_LIBRARY, PACKAGE, JAVADOC, RAW_EXECUTABLE, RAW_STATIC_LIBRARY,
COPY_HEADERS, KEY_CHAR_MAP
The snippet above includes artificial line breaks to maintain a print-friendly document.
Layers
The build hierarchy includes the abstraction layers described in the table below.
Each layer relates to the one above it in a one-to-many relationship. For example, an arch can have more than one board and each board can have more than one device. You may define an element in a given layer as a specialization of an element in the same layer, thus eliminating copying and simplifying maintenance.
Layer
|
Example
|
Description
|
Product
|
myProduct, myProduct_eu, myProduct_eu_fr, j2, sdk
|
The product layer defines a complete specification of a shipping product, defining which modules to build and how to configure them. You might offer a device in several different versions based on locale, for example, or on features such as a camera.
|
Device
|
myDevice, myDevice_eu, myDevice_eu_lite
|
The device layer represents the physical layer of plastic on the device. For example, North American devices probably include QWERTY keyboards whereas devices sold in France probably include AZERTY keyboards. Peripherals typically connect to the device layer.
|
Board
|
sardine, trout, goldfish
|
The board layer represents the bare schematics of a product. You may still connect peripherals to the board layer.
|
Arch
|
arm (arm5te) (arm6), x86, 68k
|
The arch layer describes the processor running on your board.
| Building the Android Platform
This section describes how to build the default version of Android. Once you are comfortable with a generic build, then you can begin to modify Android for your own target device.
Device Code
To do a generic build of android, source build/envsetup.sh, which contains necessary variable and function definitions, as described below.
% cd $TOP
% . build/envsetup.sh
# pick a configuration using choosecombo
% choosecombo
% make -j4 PRODUCT-generic-user
You can also replace user with eng for a debug engineering build:
% make -j4 PRODUCT-generic-eng
These Build Variants differ in terms of debug options and packages installed.
Cleaning Up
Execute % m clean to clean up the binaries you just created. You can also execute % m clobber to get rid of the binaries of all combos. % m clobber is equivalent to removing the //out/ directory where all generated files are stored.
Speeding Up Rebuilds
The binaries of each combo are stored as distinct sub-directories of //out/, making it possible to quickly switch between combos without having to recompile all sources each time.
However, performing a clean rebuild is necessary if the build system doesn't catch changes to environment variables or makefiles. If this happens often, you should define the USE_CCACHE environment variable as shown below:
% export USE_CCACHE=1
Doing so will force the build system to use the ccache compiler cache tool, which reduces recompiling all sources.
ccache binaries are provided in //prebuilt/... and don't need to get installed on your system.
Troubleshooting
The following error is likely caused by running an outdated version of Java.
device Dex: core UNEXPECTED TOP-LEVEL ERROR:
java.lang.NoSuchMethodError: method java.util.Arrays.hashCode with
signature ([Ljava.lang.Object;)I was not found.
at com.google.util.FixedSizeList.hashCode(FixedSizeList.java:66)
at com.google.rop.code.Rop.hashCode(Rop.java:245)
at java.util.HashMap.hash(libgcj.so.7)
[...]
dx is a Java program that uses facilities first made available in Java version 1.5. Check your version of Java by executing % java -version in the shell you use to build. You should see something like:
java version "1.5.0_07"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_07-164)
Java HotSpot(TM) Client VM (build 1.5.0_07-87, mixed mode, sharing)
If you do have Java 1.5 or later and your receive this error, verify that you have properly updated your PATH variable.
Building the Android Kernel
This section describes how to build Android's default kernel. Once you are comfortable with a generic build, then you can begin to modify Android drivers for your own target device.
To build the kernel base, switch to the device directory (/home/joe/android/device) in order to establish variables and run:
% . build/envsetup.sh
% partner_setup generic
Then switch to the kernel directory /home/joe/android/kernel.
Checking Out a Branch
The default branch is always android. To check out a different branch, execute the following:
% git checkout --track -b android-mydevice origin/android-mydevice
//Branch android-mydevice set up to track remote branch
% refs/remotes/origin/android-mydevice.
//Switched to a new branch "android-mydevice"
To simplify code management, give your local branch the same name as the remote branch it is tracking (as illustrated in the snippet above). Switch between branches by executing % git checkout .
Find out which branches exist (both locally and remotely) and which one is active (marked with an asterisk) by executing the following:
% git branch -a
android
* android-mydevice
origin/HEAD
origin/android
origin/android-mydevice
origin/android-mychipset
To only see local branches, omit the -a flag.
Building the Kernel
To build the kernel, execute:
% make -j4
Build Variants
When building for a particular product, it's often useful to have minor variations on what is ultimately the final release build. These are the currently-defined build variants:
eng
|
This is the default flavor. A plain make is the same as make eng.
Installs modules tagged with: eng, debug, user, and/or development.
Installs non-APK modules that have no tags specified.
Installs APKs according to the product definition files, in addition to tagged APKs.
ro.secure=0
ro.debuggable=1
ro.kernel.android.checkjni=1
adb is enabled by default.
|
user
|
make user
This is the flavor intended to be the final release bits.
Installs modules tagged with user.
Installs non-APK modules that have no tags specified.
Installs APKs according to the product definition files; tags are ignored for APK modules.
ro.secure=1
ro.debuggable=0
adb is disabled by default.
|
userdebug
|
make userdebug
The same as user, except:
Also installs modules tagged with debug.
ro.debuggable=1
adb is enabled by default.
|
If you build one flavor and then want to build another, you should run make installclean between the two makes to guarantee that you don't pick up files installed by the previous flavor. make clean will also suffice, but it takes a lot longer.
|