Akagi201
8/24/2014 - 5:00 PM
android-source.md
outline
- Android Architecture
- Compile Android include Kernel
- Android FIle System
- Android Emulator
- Application/Framework -> JNI -> Native C/C++
What is Android
- Android包括operating system, middleware和applications.
- kernel: linux
- middleware: libraries, VM, Application, Framework.
- Key applications: Phone, Browser...
GNU/Linux vs Android/Linux (cont)
- Android uses Android/Linux, not GNU/Linux.
- No native windowing system.
- No glibc support. (为了避免GPL的麻烦)
- Not include the full set of standard Linux utilities.
- User space has 3 ways to access kernel space on Linux:
/dev, /sys, /proc
Linux Kernel
- Based on Linux Kernel 2.6.
- Official first release using Linux 2.6.25 in 2008/9.
- Patch of kernel enhancements for Android.
How to Find Android Patch in Linux Kernel
- 两种方法: "1. 暴力法; 2. ctags".
find . -name "*" | xargs grep "Google, \Inc"- Drivers
- Qualcomm MSM series support.
- 改进, 文件只列一次:
find . -name "*" | xargs grep -i "android" | sed -e 's/:.*$//g' | uniq
Kernel Enhancements for Android
- Alarm - 看门狗
- Ashmem - 匿名共享内存
- Binder - IPC
- Logger - userspace runtime的日志
- Low memory killer - (4大组件: Activity, Service, Broadcast receivers, Content Provider) http://developer.android.com/guide/components/fundamentals.html
- Power management
Why Linux Kernel
- Great memory and process management
- Permission-based security model
- Proven driver model
- Open source
Native Libraries
- Bionic libc
- Function libraries
- Native servers
Bionic Libc
- Custom libc implementation, optimized for embedded use.
- Keep GPL out of user-space.
- Smaller and faster.
- Not Support certain POSIX features.
- Not compatible with GNU Libc
Function Libraries
- Media framework
- Based on PacketVideo OpenCORE platform
- Support standard video, audio, still-frame formats.
- Support for hardware / software codec plug-ins.
- SQLite
- Light-weight transactional dasta store.
- Webkit
- Based on open source WebKit browser engine.
Native Servers
- Surface manager
- Provides system-wide surface "composer", handling all surface rendering to frame buffre device.
- Can use OpenGL ES and 2D hardware accelerator for its compositions.
- Double-buffering using page-flip.
- Audio manager
- Manages all audio output devices.
- Processes multiple audio streams into PCM audio out paths.
Dalvik Virtual Machine
- Different with Java virtual machine.
- Register based.
- Customize for specific platform.
- Java .class/.jar files converted to .dex at build time, not runtime.
- Uses runtime memory very efficiently.
Application Framework / Applications
- All applications are written in Java language.
- Portability.
HAL(Harware Abstraction Layer)
- User space C/C++ library.
- Defines the interface that Android requires hardware drivers to implement.
- Why user-space HAL
- Avoid to expose proprietary IP unser GPL.
HAL Issues
- Interface
- Software layering
- mmap
- ISP
- Synchronization
- Performance
Android Project Layout
Core projects
| Project | Description |
|---|---|
| bionic | C runtime: libc, libm, libdl, dynamic linker |
| bootloader/legacy | Bootloader reference code |
| build | Build system |
| dalvik | Dalvik virtual machine |
| development | High-level development and debugging tools |
| frameworks/base | Core Android app framework libraries |
| frameworks/policies/base | Framework configuration policies |
| hardware/libhardware | Hardware abstraction library |
| hardware/rii | Radio interface layer |
| kernel | Linux kernel |
| prebuilt | Binaries to support Linux and Mac OS builds |
| recovery | System recovery environment |
| system/bluetooth | Bluetooth tools |
| system/core | Minimal bootable environment |
| system/extras | Low-level debugging/inspection tools |
| system/wlan/ti | Ti 1251 WLAN driver and tools |
Recursive Make vs Independent Make
