1.
Android Internals

2.
Course Objectives
 Develop embedded systems with Google Android
 Customize and install Google Android for your target platform
Android Internals @ SAS 2 08/23/12

3.
Course Prerequisites
 C/C++
 Basic Java
 Basic Unix/Linux command line interface experience
 An extra 1 day training may be needed.
 Embedded systems development is a plus.
Android Internals @ SAS 3 08/23/12

4.
Course Notes
 Ask any time.
 Set your cell to silent.
 Course assumes Linux is already ported to your hardware.
 An extra 5 days training may be needed.
Android Internals @ SAS 4 08/23/12

5.
Outline
Lectures Labs
 Introduction to Android  Android Source Code
 Android Source Code & Compilation  1st Compilation
 Linux Kernel Introduction  Compile and Boot an Android Kernel
 Changes Introduced in the Android
Kernel
 Android Booting Scenarios  Supporting a New Board
 Developing and Debugging with ADB  Use ADB
 Android Filesystem Layout
 Android Build System  System Customization
 Android Native Layer  Building a Library
 Adding a Native Application to the
Build
Android Internals @ SAS 5 08/23/12

6.
How does Embedded Linux System
Boot?
 We will talk about bootloader and Init process only.
Android Internals @ SAS 6 08/23/12

7.
What does a Bootloader do?
 Basic HW initialization
 Loading of an application binary, usually an operating system kernel
 Decompression of the application binary
 Execution of the application
 Most bootloaders provide a shell with various commands implementing
different operations.
 Loading data
 Memory inspection
 HW diagnostics
 Testing
 ...
Android Internals @ SAS 7 08/23/12

8.
PC Boatloaders
 BIOS executes from on board
ROM.
 Basic HW initialization + 1st
BIOS bootloader loading
 1st stage bootloader loads a full
1st stage bootloader boatloader.
 Full bootloader with full
functionality and features.
Full boatloader
 It can load a kernel from a
filesystem.
Kernel  Examples:
 GRUB
 Syslinux
Android Internals @ SAS 8 08/23/12

9.
Booting on Embedded CPUs – NOR
Flash
 CPU starts executing code at a
fixed address when powered up.
 HW design ensures that a NOR
flash is at this address.
 It can hold the 1st stage
bootloader or even a full
bootloader.
 NOR flashes are very expensive
and limited in size.
 Not very common nowdays
Android Internals @ SAS 9 08/23/12

10.
Booting on Embedded CPUs – !NOR
Flash
 ROM code is stored in an internal
ROM in the CPU.
ROM code
 ROM code loads bootstrap
bootloader from non-volatile
Bootstrap bootloader storage into SRAM.
Full boatloader  Bootstrap loads full bootloader
into DRAM which in return loads
the kernel in the DRAM.
Kernel
Android Internals @ SAS 10 08/23/12

11.
Examples of Embedded Bootloaders
 U-Boot
 http://www.denx.de/wiki/U-Boot
 Barebox
 http://www.barebox.org
 Redboot
 Yaboot
 PMON
 ...
Android Internals @ SAS 11 08/23/12

12.
Android Bootloader
 The bootloader is outside the realm of Android itself.
 The first-stage bootloader will provide support for:
 Loading recovery images to the system flash
 Putting the device into a mode where the developer can perform
development tasks
 AKA fastboot mode
 These features should be disabled in production.
 In addition, it supports normal booting sequence.
Android Internals @ SAS 12 08/23/12

13.
What is Fastboot?
 A protocol to communicate bootloaders over USB.
 It is synchronous and driven by the host.
 Accessible with the fastboot command.
 Allows to:
 Transmit data
 Flash the various partitions of the device
 Get variables from the bootloader
 Control the boot sequence
Android Internals @ SAS 13 08/23/12

14.
Fastboot Usage
1. Make sure that ADB or SDK installed on host.
2. Install fastboot for your host.
3. Turn off the device.
4. Boot device into bootloader.
5. Make sure the device is in FASTBOOT and not HBOOT.
6. Connect the device to the computer via USB.
7. On your computer, open terminal and run fastboot command.
Android Internals @ SAS 14 08/23/12

15.
Fastboot Command
 Usage: fastboot [ <option> ] <command>
Command Description
update <filename> Reflash device from filename
flashall Flash boot + recovery + system
flash <partition> [ <filename> ] Write a file to a flash Partion
erase <partition> Erase a flash partition
getvar <variable> Display a bootloader variable
boot <kernel> [ <ramdisk> ] Download and boot kernel
flash:raw boot <kernel> [ <ramdisk> ] Create bootimage and flash it
devices List all connected devices
continue Continue with autoboot
reboot Reboot device normally
reboot-bootloader Reboot device into bootloader
Android Internals @ SAS 15 08/23/12

16.
Fastboot Command cont’d
Option Description
-w Erase userdata and cache
-s <serial number> Specify device serial number
-p <product> Specify product name
-c <cmdline> Override kernel commandline
-i <vendor id> Specify a custom USB vendor id
-b <base_addr> Specify a custom kernel base address
-n <page size> Specify the nand page size. default:2048
Android Internals @ SAS 16 08/23/12

17.
Fastboot Session Example
Android Internals @ SAS 17 08/23/12

18.
Init Starts Daemons
 Including
 usbd
 adbd
 debuggerd
 rild
 ...
Daemon
Daemon
Daemon
Init
Android Internals @ SAS 18 08/23/12

19.
Init Starts Zygote Process
 A Zygote process:
 Initializes a Dalvik VM instance
 Loads classes
 Listens for requests to spawn VMs
 Forks on requests VMs using copy-on-write to minimize footprint
Daemon
Daemon Zygote
Daemon
Init
Android Internals @ SAS 19 08/23/12

20.
Init Starts Runtime Process
 A runtime process:
 Initializes a service manager and
registers it as a default context
manager for Binder services
Service
Manager
Daemon
Daemon Runtime Zygote
Daemon
Init
Android Internals @ SAS 20 08/23/12

21.
Runtime Requests to Start the System
Server Process
 Requested from Zygote
 Zygote forks a new VM for the system server process and starts the
server.
System
Server
Service Dalvik
Manager VM
Daemon
Daemon Runtime Zygote
Daemon
Init
Android Internals @ SAS 21 08/23/12

22.
System Server Starts the Native
System Servers
 Including:
 Surface flinger
 Audio flinger
 ... Daemon
Daemon
Flingers
System
 Native system servers register Server
with service manager as IPC
Service Dalvik
service targets.
Manager VM
Daemon
Daemon Runtime Zygote
Daemons
Init
Android Internals @ SAS 22 08/23/12

23.
System Server Starts the Android
Managed Services
 Including
 Content manager
 Window manager
 Telephony service Daemon
Daemon Daemon
Daemon
Flingers Managers
 Activity manager
 …
System
Server
Service Dalvik
Manager VM
Daemon
Daemon Runtime Zygote
Daemon
Init
Android Internals @ SAS 23 08/23/12

24.
Android Managed Services Register
with the Service Manager
Daemon
Daemon Daemon
Daemon
Flingers Managers
System
Server
Service Dalvik
Manager VM
Daemon
Daemon Runtime Zygote
Daemon
Init
Android Internals @ SAS 24 08/23/12

25.
Android Startup Overview
System Startup
Android Internals @ SAS 25 08/23/12

26.
Android Startup Overview – Home
Window
libc
Android Internals @ SAS 26 08/23/12

27.
Android Startup Overview – Any
Application
libc
Android Internals @ SAS 27 08/23/12

28.
How do Layers Interact?
 There are 3 main scenarios for the app to talk to the native libraries.
 Directly
 Through a service
 Through a daemon
 Depends on:
Applications
 Application
 Native library implementation Application Framework
 Android version Libraries
Linux Kernel
Android Internals @ SAS 28 08/23/12

29.
Direct Layers Interaction
Applications
Application
Binder IPC
Application
Framework
Runtime Service
JNI
Native Service Binding
Libraries
Dynamic Loading
HAL Library
Linux Kernel
Device Driver
Android Internals @ SAS 29 08/23/12

30.
Direct Layers Interaction – Location
ManagerApplications
Application
Binder IPC
Application
Framework
Location Manager Service
GPS Location Provider
JNI
GPS Location Provider Binder
Libraries
Dynamic Loading
libgps.so
Linux Kernel
GPS Device Driver
Android Internals @ SAS 30 08/23/12

31.
Through a Service Layers Interaction
Applications
Application
Binder IPC
Application
Framework
Runtime Service
JNI
Binder IPC
Native Service Binding Native Service
Libraries
Dynamic Loading
HAL Library
Linux Kernel
Device Driver
Android Internals @ SAS 31 08/23/12

32.
Through a Service Layers Interaction –
Media Player
Applications
Application
Binder IPC
Application
Framework
Media Player
JNI
Binder IPC
Media Player Binder Audio Flinger
Libraries
Dynamic Loading
Media Framework
libaudio.so
Linux Kernel
ALSA
Speakers Device Driver
Android Internals @ SAS 32 08/23/12

33.
Through a Daemon Layers Interaction
Applications
Application
Binder IPC
Application
Framework
Runtime Service
JNI
Sockets
Native Service Binding Native Daemon
Libraries
Dynamic Loading
HAL Library
Linux Kernel
Device Driver
Android Internals @ SAS 33 08/23/12

34.
Android Internals @ SAS 34 08/23/12