Android presentation

1. Android Architecture

2. Agenda ● Linux Kernel ● Native Libraries ● Android Runtime ● Application Framework ● Inside The System Connectivity(Bluetooth,WiFi...) Power Management Display & Multimedia (Surfaceflinger, Audioflinger,Camera/Video) Telephony (Radio Interface Layer) ● Android Boot sequence ● Layer Interaction

3. Android System Architecture

5. Linux Kernel ● Android is built on the Linux kernel, but Android is not Linux ● No native windowing system ● Does not include the full set of standard Linux utilities ● Patch of “kernel enhancements” to support Android

6. Why Linux Kernel? ● Great memory and process management ● Permissions-based security model ● Proven driver model ● Support for shared libraries ● It's already open source!

7. Kernel Enhancements • Binder • Power Management

8. Binder: Problem ● Applications and Services may run in separate processes but must communicate and share data ● IPC can introduce significant processing overhead and security holes

9. Binder: Solution ● Driver to facilitate inter-process communication (IPC) ● High performance through shared memory ● Per-process thread pool for processing requests ● Reference counting, and mapping of object references across processes ● Synchronous calls between processes

10. Binder in Action

17. Binder Android Interface Definition Language (AIDL) http://developer.android.com/guide/components/aidl.html

18. PM Problem ● Mobile devices run on battery power ● Batteries have limited capacity

19. PM Solution ● Built on top of standard Linux Power Management (PM) ● More aggressive power management policy ● Components make requests to keep the power on through “wake locks” ● Supports different types of wake locks

20. Android PM in Action

26. Android PM ● Use wake locks carefully! ● sysfs entries for wakelocks in android "/sys/power/wake_lock", "/sys/power/wake_unlock", "/sys/power/state"

27. Kernel Download and Build android kernel from: http://source.android.com/source/building- kernels.html

29. Native Libraries

30. Native Libraries ● Bionic Libc ● Function Libraries ● Native Servers ● Hardware Abstraction Libraries

32. What is Bionic? ● What is bionic? Custom libc implementation, optimized for embedded use.

33. What is Bionic? Why build a custom libc library? ● License: we want to keep GPL out of user- space ● Size: will load in each process, so it needs to be small ● Fast: limited CPU power means we need to be fast

34. Bionic libc ● BSD License ● Small size and fast code paths ● Very fast and small custom pthread implementation

35. Bionic libc ● Built-in support for important Android- specific services a. system properties getprop(“my.system.property”, buff, default); b. log capabilities LOGI(“Logging a message with priority ‘Info’”);

37. WebKit ● Based on open source WebKit browser: http: //webkit.org ● Renders pages in full (desktop) view ● Full CSS, Javascript, DOM, AJAX support ● Support for single-column and adaptive view rendering

38. Media Framework ● Based on PacketVideo OpenCORE platform ● Supports standard video, audio, still-frame formats ● Support for hardware / software codec plug- ins

39. SQLite ● Light-weight transactional data store ● Back end for most platform data storage

41. Surface Flinger ● Provides system-wide surface “composer”, handling all surface rendering to frame buffer device ● Can combine 2D and 3D surfaces and surfaces from multiple applications

42. Surface Manager ● Surfaces passed as buffers via Binder IPC calls ● Can use OpenGL ES and 2D hardware accelerator for its compositions ● Double-buffering using page-flip

43. Audio Flinger ● Manages all audio output devices ● Processes multiple audio streams into PCM audio out paths ● Handles audio routing to various outputs

45. Hardware Abstraction Layer

46. Hardware Abstraction Libraries ● Why do we need a user-space HAL? ○ Not all components have standardized kernel driver interfaces ○ Kernel drivers are GPL which exposes any proprietary IP ○ Android has specific requirements for hardware drivers

47. Hardware Abstraction Libraries ● Libraries are loaded dynamically at runtime as needed QualcommCameraHardware.cpp ... libqcamera = dlopen(“/system/lib/liboemcamera.so”, TLD_NOW); ... *(void **)&LINK_camera_init = ::dlsym(libqcamera, "camera_init"); ... LINK_camera_init();

49. Android Runtime

50. What is the Dalvik VM? ● Android's custom clean-room implementation virtual machine ● run on a slow CPU ● with relatively little RAM ● on an OS without swap space ● while powered by a battery

51. Dalvik Virtual Machine ● Provides application portability and runtime consistency ● Runs optimized file format (.dex) and Dalvik bytecode ● Java .class / .jar files converted to .dex at build time

52. Core Libraries ● Core APIs for Java language provide a powerful, yet simple and familiar development platform ○ Data structures ○ Utilities ○ File access ○ Network Access ○ Graphics ○ …

53. .dex file

54. .jar Vs .dex

55. .class files

56. .dex file

58. Application Framework

59. Core Platform Services ● Services that are essential to the Android platform ● Behind the scenes - applications typically don't access them directly

60. Core Platform Services ● Activity Manager

61. Core Platform Services ● Activity Manager ● Package Manager

62. Core Platform Services ● Activity Manager ● Package Manager ● Window Manager

63. Core Platform Services ● Activity Manager ● Package Manager ● Window Manager ● Resource Manager

64. Core Platform Services ● Activity Manager ● Package Manager ● Window Manager ● Resource Manager ● Content Providers

65. Core Platform Services ● Activity Manager ● Package Manager ● Window Manager ● Resource Manager ● Content Providers ● View System

66. Hardware Services ● Provide access to lower-level hardware APIs ● Typically accessed through local Manager object LocationManager lm = (LocationManager) Context.getSystemService (Context.LOCATION_SERVICE);

67. Hardware Services ● Telephony Service

68. Hardware Services ● Telephony Service ● Location Service

69. Hardware Services ● Telephony Service ● Location Service ● Bluetooth Service

70. Hardware Services ● Telephony Service ● Location Service ● Bluetooth Service ● WiFi Service

71. Hardware Services ● Telephony Service ● Location Service ● Bluetooth Service ● WiFi Service ● USB Service

72. Hardware Services ● Telephony Service ● Location Service ● Bluetooth Service ● WiFi Service ● USB Service ● Sensor Service

73. Android System

75. Inside The System ● Connectivity ○ Bluetooth ○ WiFi ● Power Management ● Display & Multimedia ○ Display Subsystem ○ Audio Subsystem ○ Camera/Video Subsystem ● Telephony

76. Connectivity ● Bluetooth ● Wi-Fi

77. Bluetooth Note: Android 4.2 introduces a new Bluetooth stack optimized for use with Android devices. The new Bluetooth stack developed in collaboration between Google and Broadcom replaces the stack based on BlueZ and provides improved compatibility and reliability.

78. Wi-Fi ● Android uses wpa_supplicant as the platform interface to the Wi-Fi device. ● Your Wi-Fi driver must be compatible with the standard wpa_supplicant

79. Wi-Fi

81. Power Management

83. Display & Multimedia ● Display Subsystem ● Audio Subsystem ● Camera/Video Subsystem

84. Display Subsystem

85. Audio Subsystem

86. Camera/Video Subsystem

87. Android Multimedia Framework

89. Telephony ● Radio Interface Layer Android's Radio Interface Layer (RIL) provides an abstraction layer between Android telephony services (android.telephony) and radio hardware.

90. Radio Interface Layer

92. Runtime Walkthrough It all starts with init… Similar to most Linux-based systems at startup, the bootloader loads the Linux kernel and starts the init process.

93. Runtime Walkthrough ● Init starts Linux daemons, including: ○ USB Daemon (usbd) to manage USB connections ○ Android Debug Bridge (adbd) to manage ADB connections ○ Debugger Daemon (debuggerd) to manage debug processes requests (dump memory, etc.) ○ Radio Interface Layer Daemon (rild) to manage communication with the radio

94. Runtime Walkthrough ● Init process starts the zygote process: ○ A nascent process which initializes a Dalvik VM instance ○ Loads classes and listens on socket for requests to spawn VMs ○ Forks on request to create VM instances for managed processes ○ Copy-on-write to maximize re-use and minimize footprint

95. Runtime Walkthrough ● Init starts runtime process: ○ Initializes Service Manager – the context manager for Binder that handles service registration and lookup ○ Registers Service Manager as default context manager for Binder services

96. Runtime Walkthrough ● Runtime process sends request for Zygote to start System Service

97. Runtime Walkthrough ● Runtime process sends request for Zygote to start System Server ○ Zygote forks a new VM instance for the System Service process and starts the service

98. Runtime Walkthrough ● System Service starts the native system servers, including: ○ Surface Flinger ○ Audio Flinger

99. Runtime Walkthrough ● Native system servers register with Service Manager as IPC service targets:

100. Runtime Walkthrough ● System Service starts the Android managed services:

101. Runtime Walkthrough ● Android managed Services register with Service Manager:

102. Runtime Walkthrough

103. Runtime Walkthrough After system server loads all services, the system is ready…

106. Runtime Walkthrough Each subsequent application is launched in it's own process

108. Layer Interaction There are 3 main flavors of Android layer cake: ○ App Runtime Service lib ○ App Runtime Service Native Service lib ○ App Runtime Service Native Daemon lib

110. Android Runtime Services

114. Example: Location Manager

116. Android Native Services

124. Daemon Connection

128. Questions

Android presentation

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