Source Code Overview

Introduction
Android Source
Adding Source Code

Introduction

Android source code is maintained in two code bases: the Android Linux kernel (kernel directory) and Android platform and applications (device directory). This document provides a high-level introduction to the source code organization and an overview of the major components of each primary directory.

Android Source

Linux Kernel

The Android Linux kernel includes enhancements to the Linux 2.6 kernel that provide additional drivers to support the Android platform, including:

  • Binder: an OpenBinder-based driver to facilitate inter-process communication (IPC) in the Android platform.
  • Android Power Management: a light weight power management driver built on top of standard Linux power management but optimized for embedded systems.
  • Low Memory Killer: Based on hints from the userspace, the low memory killer can kill off processes to free up memory as necessary. It is designed to provide more flexibility than the Out Of Memory (OOM) killer in the standard kernel.
  • Logger: A light weight logging device used to capture system, radio, logdata, etc.
  • USB Gadget: Uses the USB function framework.
  • Android/PMEM: The PMEM (physical memory) driver is used to provide contiguous physical memory regions to userspace libraries that interact with the digital signal processor (DSP) and other hardware that cannot cope with scatter-gather.
  • Android Alarm: A driver which provides timers that can wake the device up from sleep and a monotonic timebase that runs while the device is asleep.

Look for Android-specific enhancements in the following directories:

  • /drivers/android
  • /drivers/misc
  • /include/linux

Android Platform and Applications

The following list outlines the directory structure found within the device branch of Android source code:

  • apps Core Android applications such as Phone, Camera, and Calendar.
  • boot Reference Android bootloader and other boot-related source code.
  • commands Common Android commands, the most important of which is the runtime command, which does much of the initialization of the system.
  • config System-wide makefiles and linker scripts.
  • content Standard Android ContentProvider modules.
  • dalvik Android runtime Virtual Machine (VM).
  • data Fonts, keymaps, sounds, timezone information, etc.
  • docs Full set of Android documentation.
  • extlibs Non-Android libraries. This directory is intended to host unmodified external code. None of the libraries included within this directory rely on Android headers or libraries.
  • ide Tools for support of the IDE's used to write Android applications.
  • include Android system headers for inclusion.
  • java Android core APIs, as well as some external libraries.
  • libs Android-specific C++ based libraries.
  • partner Project-specific source code for various proprietary components.
  • prebuilt Prebuilt tools, like the toolchains and emulator binary.
  • product Device-specific configuration files. This directory will include a subdirectory for each new device.
  • samples Sample applications.
  • servers C++ based system servers.
  • system Core of the embedded Linux platform at the heart of Android. These essential bits are required for basic booting, operation, and debugging.
  • tests Platform and application test cases.
  • tools Tools for building and debugging Android (of particular interest for porting are "adb" and "emulator").

Adding Source Code

You can develop Android applications with the same standard tools you use to develop any Java application. The Android core libraries provide the functionality needed to build rich mobile applications and the Android development tools are designed to simplify running, debugging, and testing your applications.

Add project-specific source code to the Android source tree under the partner directory in a directory specific to the application or service you are building. For example, all Google-specific applications would be placed under vendor/google/. A Google search application would be placed under vendor/google/apps/Search.

See Building Android for a new Mobile Device for detailed instructions.

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