This document provides an overview of the Android system architecture. It describes the key components including the Linux kernel, native libraries like Bionic and SQLite, the Android runtime using the Dalvik VM, and the application framework. It also covers core platform services, hardware services, and internal system components for connectivity, power management, display/multimedia, and telephony. The document outlines how these layers interact and provides technical details on implementations like Binder IPC and the SurfaceFlinger compositor.

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

4. 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

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

11. Binder in Action

12. Binder in Action

13. Binder in Action

14. Binder in Action

15. Binder in Action

16. 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

21. Android PM in Action

22. Android PM in Action

23. Android PM in Action

24. Android PM in Action

25. 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

28. 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

29. Native Libraries

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

31. 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’”);

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

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

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

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

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

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();

48. 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

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

57. 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

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

74. 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

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

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

81. Power Management

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

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

84. Display Subsystem

85. Audio Subsystem

86. Camera/Video Subsystem

87. Android Multimedia Framework

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

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

91. 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

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…

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

105. 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

107. 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

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

109. 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

111. Android Runtime Services

112. Android Runtime Services

113. Android Runtime Services

114. Example: Location Manager

115. 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

116. Android Native Services

117. Android Native Services

118. Android Native Services

119. Android Native Services

120. Android Native Services

121. Android Native Services

122. Android Native Services

123. 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

124. Daemon Connection

125. Daemon Connection

126. Daemon Connection

127. Daemon Connection

128. Questions