BSP Developer Must Know about Android.pdf

BSP Developer Must Know about Android.pdf

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BSP Developer Must Know about
Android

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Revision History
Revision No. Description Date
V1.0 •Android concepts for BSP developer, by Yone Xie 2012-07-19
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 2
F-3697 Security Level: Confidential A

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Agenda
Intro⊿
Android Architecture
Linux Kernel
Native Libraries
Android Runtime
Application Framework
Android Applications
Android Concepts
Key Concepts
Start-up Walkthrough
Layer Interaction
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 3 Security Level: Confidential A

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History

1.0 - September 23, 2008
1.5 - Cupcake
1.6 - Donut
2.1 - Eclair
2.2 - Froyo
2.3 - Gingerbread
3.x - Honeycomb
4.0 - Ice Scream Sandwich
4.1 - Jelly Bean
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 4 Security Level: Confidential A

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AOSP(Android Open Source Project)
At every new version, Google releases its source code through this
project so that community and vendors can work with it.
One major exception: Honeycomb has not been released because Google
stated that its source code was not clean enough to release it.
One can fetch the source code and contribute to it, even though
the development process is very locked by Google
Only a few devices are supported through AOSP though, only the
two most recent Android development phones, the Panda board
and the Motorola Xoom.
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 5 Security Level: Confidential A

6. F-3697
Agenda
Intro
Android Architecture ⊿
Linux Kernel
Native Libraries
Android Runtime
Application Framework
Android Applications
Android Concepts
Key Concepts
Start-up Walkthrough
Layer Interaction
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 6 Security Level: Confidential A

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Android Architecture
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 7 Security Level: Confidential A
Applications
Launcher2 Contacts Phone Browser ...
Libraries
Surface Manager Media Framework SQLite
Open GL | ES FreeType WebKit
SGL SSL Bionic
Android Runtime
Core
Libraries
Dalvik
Virtual Machine
Linux Kernel
Display Driver Camera Driver Bluetooth Driver
Binder (IPC)
Driver
USB Driver
Keypad/Touch
Driver
WiFi Driver
Power
Management
Shared Memory
Driver
Audio Driver
Application Framework
Activity Manager Window Manager
Content
Provider
View System
Package Manager
Telephony
Manager
Resource
Manager
… Location Manager
Notification
Manager

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Linux Kernel
Used as the foundation of the Android system
Why Linux kernel?
But, Android is not Linux
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 8 Security Level: Confidential A
Linux Kernel
Display Driver Camera Driver Bluetooth Driver
Binder (IPC)
Driver
USB Driver
Keypad/Touch
Driver
WiFi Driver
Power
Management
Shared Memory
Driver
Audio Driver

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Linux Kernel
Android vs. Linux Distributions
XNo native window GUI system (GNOME/KDE)
XNo glibc support
XDoes not include the full set of standard Linux utilities
Standard Linux Kernel (version 2.6+)
XPatches of “kernel enhancements” to support Android

Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 9 Security Level: Confidential A
Linux Kernel
Display Driver Camera Driver Bluetooth Driver
Binder (IPC)
Driver
USB Driver
Keypad/Touch
Driver
WiFi Driver
Power
Management
Shared Memory
Driver
Audio Driver

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Kernel Patches
Kernel patches for Android by Google
Alarm
Ashmem
Binder
Power Management
Low Memory Killer
Kernel Debugger
Logger
These changes are beginning to go into the staging/ area of the kernel, as of
3.3, after being a complete fork for a long time

Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 10 Security Level: Confidential A
Linux Kernel
Display Driver Camera Driver Bluetooth Driver
Binder (IPC)
Driver
USB Driver
Keypad/Touch
Driver
WiFi Driver
Power
Management
Shared Memory
Driver
Audio Driver

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Binder : Problem
Why need Binder IPC mechanisms?
Applications and Services may run in separate processes but must
communicate and share data
Inter-process communication (IPC) can introduce significant processing
overhead and security holes
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 11 Security Level: Confidential A
Linux Kernel
Display Driver Camera Driver Bluetooth Driver
Binder (IPC)
Driver
USB Driver
Keypad/Touch
Driver
WiFi Driver
Power
Management
Shared Memory
Driver
Audio Driver

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Binder : Solution
Binder IPC mechanisms
Driver to facilitate 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
“In the Android platform, the binder is used for nearly everything that
happens across processes in the core platform. "
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 12 Security Level: Confidential A
Linux Kernel
Display Driver Camera Driver Bluetooth Driver
Binder (IPC)
Driver
USB Driver
Keypad/Touch
Driver
WiFi Driver
Power
Management
Shared Memory
Driver
Audio Driver

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Binder in Action
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 13 Security Level: Confidential A
Process A
App A Context Binder Driver
Process B
Service B
Get service
Service
Call foo (object)
Call Return
Marshal proxy
object
Relay to
IPC threads

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Binder
How to use Binder from App developer’s view?
Intent
Android Interface Definition Language (AIDL)
http://developer.android.com/guide/components/aidl.html
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 14 Security Level: Confidential A
Linux Kernel
Display Driver Camera Driver Bluetooth Driver
Binder (IPC)
Driver
USB Driver
Keypad/Touch
Driver
WiFi Driver
Power
Management
Shared Memory
Driver
Audio Driver

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PM : Problem
Why Android need special power management?
Mobile devices run on battery power
Batteries have limited capacity
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 15 Security Level: Confidential A
Linux Kernel
Display Driver Camera Driver Bluetooth Driver
Binder (IPC)
Driver
USB Driver
Keypad/Touch
Driver
WiFi Driver
Power
Management
Shared Memory
Driver
Audio Driver

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PM : Solution
Why Android need special power management?
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
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 16 Security Level: Confidential A
Linux Kernel
Display Driver Camera Driver Bluetooth Driver
Binder (IPC)
Driver
USB Driver
Keypad/Touch
Driver
WiFi Driver
Power
Management
Shared Memory
Driver
Audio Driver

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Android PM in Action
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 17 Security Level: Confidential A
App A Power Manager PM Driver
New Wake Lock
PARTIAL
Create Wake Lock
Release
Release
Turn Off
CPU
Turn Off
LCD

18. F-3697
Android PM
How to use Android PM from App developer’s view?
android.os.PowerManager
Use wake locks carefully!
userActivity(long when, …)
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 18 Security Level: Confidential A
Linux Kernel
Display Driver Camera Driver Bluetooth Driver
Binder (IPC)
Driver
USB Driver
Keypad/Touch
Driver
WiFi Driver
Power
Management
Shared Memory
Driver
Audio Driver

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Get Linux Kernel for Android
Get kernel source from Google, Depending on which kernel you
want
git clone https://android.googlesource.com/kernel/common.git
git clone https://android.googlesource.com/kernel/exynos.git
git clone https://android.googlesource.com/kernel/goldfish.git
git clone https://android.googlesource.com/kernel/msm.git
git clone https://android.googlesource.com/kernel/omap.git
git clone https://android.googlesource.com/kernel/samsung.git
git clone https://android.googlesource.com/kernel/tegra.git
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 19 Security Level: Confidential A
Linux Kernel
Display Driver Camera Driver Bluetooth Driver
Binder (IPC)
Driver
USB Driver
Keypad/Touch
Driver
WiFi Driver
Power
Management
Shared Memory
Driver
Audio Driver

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Native Libraries
Gather a lot of Android-specific libraries to interact at a low-level
with the system(such as HAL), but third-parties libraries as well
Bionic LibC
Function Libraries
Native Servers
Hardware Abstraction Libraries
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 20 Security Level: Confidential A
Libraries
Surface Manager Media Framework SQLite
Open GL | ES FreeType WebKit
SGL SSL Bionic
Android Runtime
Core
Libraries
Dalvik
Virtual Machine

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Bionic
What is bionic?
Custom libc implementation, optimized for embedded use.
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 21 Security Level: Confidential A
Libraries
Surface Manager Media Framework SQLite
Open GL | ES FreeType WebKit
SGL SSL Bionic
Android Runtime
Core
Libraries
Dalvik
Virtual Machine

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Bionic : Problem
Why build a custom libc library?
License: Google wants to keep GPL out of user-space
Size: will load in each process, so it needs to be small
Fast: limited CPU power means it should to be fast
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 22 Security Level: Confidential A
Libraries
Surface Manager Media Framework SQLite
Open GL | ES FreeType WebKit
SGL SSL Bionic
Android Runtime
Core
Libraries
Dalvik
Virtual Machine

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Bionic : Solution
Bionic is :
BSD License
Small size and fast code paths
Very fast and small custom pthread implementation
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 23 Security Level: Confidential A
Libraries
Surface Manager Media Framework SQLite
Open GL | ES FreeType WebKit
SGL SSL Bionic
Android Runtime
Core
Libraries
Dalvik
Virtual Machine

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Bionic
Built-in support for important Android-specific services
Access to system properties
getprop(“my.system.property”, buff, default);
setprop (“my.system.property”, value);
Logging events in the system logs
LOGD(“Logging a message with priority ‘Debug’”);
LOGW(“Logging a message with priority ‘Warning’”);
LOGE(“Logging a message with priority ‘Error’”);
LOGI(“Logging a message with priority ‘Info’”);
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 24 Security Level: Confidential A

25. F-3697
Bionic
Bionic C library with the following weirdness :
Non POSIX
No support for locales
No support for wide chars (i.e. multi-byte characters)
Comes with its own smallish implementation of pthreads based on Linux
futexes
C++ exceptions are not supported
pthread cancellation is NOT supported
Several functions are just stubs (i.e. runtime weirdness may happen)
Non standard /etc config files
Dynamic user/groups management (no pam, group, passwd or shadow)
No fstab
No SysV init
All native code must be compiled against bionic
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 25 Security Level: Confidential A

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Function Libraries
Media Framework
Based on Stagefright platform (Android introduces Stagefright to replace
OpenCORE start from Eclair)
Supports standard video, audio, still-frame formats
Support for hardware / software codec plug-ins
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 26 Security Level: Confidential A
Libraries
Surface Manager Media Framework SQLite
Open GL | ES FreeType WebKit
SGL SSL Bionic
Android Runtime
Core
Libraries
Dalvik
Virtual Machine

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Function Libraries
SQLite
Light-weight transactional data store
Back end for most platform data storage
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 27 Security Level: Confidential A
Libraries
Surface Manager Media Framework SQLite
Open GL | ES FreeType WebKit
SGL SSL Bionic
Android Runtime
Core
Libraries
Dalvik
Virtual Machine

28. F-3697
Function Libraries
Open GL | ES
3D graphics engine
An implementation based on OpenGL ES 1.0 APIs

Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 28 Security Level: Confidential A
Libraries
Surface Manager Media Framework SQLite
Open GL | ES FreeType WebKit
SGL SSL Bionic
Android Runtime
Core
Libraries
Dalvik
Virtual Machine

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Function Libraries
SGL
Scalable Graphics Library (Skia Graphics Library)
2D graphics engine
low-level graphics library implemented in native code that handles
rendering - Text, Geometries, and Images
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 29 Security Level: Confidential A
Libraries
Surface Manager Media Framework SQLite
Open GL | ES FreeType WebKit
SGL SSL Bionic
Android Runtime
Core
Libraries
Dalvik
Virtual Machine

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Function Libraries
FreeType
A font rasterization engine, used to render text to bitmaps and provides
support for other font-related operations
http://freetype.org
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 30 Security Level: Confidential A
Libraries
Surface Manager Media Framework SQLite
Open GL | ES FreeType WebKit
SGL SSL Bionic
Android Runtime
Core
Libraries
Dalvik
Virtual Machine

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Function Libraries
SSL
Open SSL library, an open-source implementation of the SSL and TLS
protocols
http://openssl.org
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 31 Security Level: Confidential A
Libraries
Surface Manager Media Framework SQLite
Open GL | ES FreeType WebKit
SGL SSL Bionic
Android Runtime
Core
Libraries
Dalvik
Virtual Machine

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Function Libraries
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
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 32 Security Level: Confidential A
Libraries
Surface Manager Media Framework SQLite
Open GL | ES FreeType WebKit
SGL SSL Bionic
Android Runtime
Core
Libraries
Dalvik
Virtual Machine

33. F-3697
Native Services
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
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 33 Security Level: Confidential A
Libraries
Surface Manager Media Framework SQLite
Open GL | ES Audio Manager WebKit
SGL SSL Bionic
Android Runtime
Core
Libraries
Dalvik
Virtual Machine

34. F-3697
Native Services
Surface Flinger
Surfaces passed as buffers via Binder IPC calls
Can use OpenGL ES and 2D hardware accelerator for its compositions
Double-buffering using page-flip (and Triple-buffering introduced from Jelly
Bean)
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 34 Security Level: Confidential A
Libraries
Surface Manager Media Framework SQLite
Open GL | ES Audio Manager WebKit
SGL SSL Bionic
Android Runtime
Core
Libraries
Dalvik
Virtual Machine

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Typical Graphical Stacks
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 35 Security Level: Confidential A

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Surface Flinger
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 36 Security Level: Confidential A

37. F-3697
Native Services
Audio Flinger
Manages all audio output devices
Processes multiple audio streams into PCM audio out paths
Handles audio routing to various outputs
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 37 Security Level: Confidential A
Libraries
Surface Manager Media Framework SQLite
Open GL | ES Audio Manager WebKit
SGL SSL Bionic
Android Runtime
Core
Libraries
Dalvik
Virtual Machine

38. F-3697
Audio Flinger
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 38 Security Level: Confidential A

39. F-3697
Hardware Abstract Layer
Graphics Audio/Camera
WiFi /GPS/
Bluetooth
RIL ...
HAL
Hardware Abstraction Layer / Libraries
Where is it?
Usually, the kernel already provides a HAL for user-space
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 39 Security Level: Confidential A
Libraries
Surface Manager Media Framework SQLite
Open GL | ES FreeType WebKit
SGL SSL Bionic
Android Runtime
Core
Libraries
Dalvik
Virtual Machine
Linux Kernel
Display Driver Camera Driver Bluetooth Driver
Binder (IPC)
Driver
USB Driver
Keypad/Touch
Driver
WiFi Driver
Power
Management
Shared Memory
Driver
Audio Driver

40. F-3697
HAL : Problem
Why do Android need a user-space HAL?
Kernel drivers are GPL which exposes any proprietary IP
Not all components have standardized kernel driver interfaces
Android has specific requirements for hardware drivers
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 40 Security Level: Confidential A
Linux Kernel
Display Driver Camera Driver Bluetooth Driver
Binder (IPC)
Driver
USB Driver
Keypad/Touch
Driver
WiFi Driver
Power
Management
Shared Memory
Driver
Audio Driver
Hardware Abstract Layer
Graphics Audio/Camera
WiFi /GPS/
Bluetooth
RIL ...

41. F-3697
HAL : Solution
Android HAL :
Defines the interface that Android requires hardware “drivers” to
implement
Separates the Android platform logic from the hardware interface
And Google implemented its HAL with dynamically loaded user-space
libraries
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 41 Security Level: Confidential A
Linux Kernel
Display Driver Camera Driver Bluetooth Driver
Binder (IPC)
Driver
USB Driver
Keypad/Touch
Driver
WiFi Driver
Power
Management
Shared Memory
Driver
Audio Driver
Hardware Abstract Layer
Graphics Audio/Camera
WiFi /GPS/
Bluetooth
RIL ...

42. F-3697
HAL : Details
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 42 Security Level: Confidential A
Loading and Interfacing Methods
dlopen() - loading through HAL
Linker-loaded .so files
Hardcoded dlopen()s
Sockets
Sysfs entries
/dev nodes
D-Bus

43. F-3697
HAL : Details
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 43 Security Level: Confidential A
HAL Header Example
// must be provided by each Acme hardware implementation


typedef struct {
int (*foo)( void );
char (*bar)( void );
...
} AcmeFunctions;


const AcmeFunctions *Acme_Init(const struct Env *env, int argc,
char **argv);

44. F-3697
HAL : Details
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 44 Security Level: Confidential A
Libraries are loaded dynamically at runtime as needed
dlHandle = dlopen(“/system/lib/ libacme.so”, RTLD_NOW);

...

acmeInit = (const AcmeFunctions *(*)(const struct Env *,
int, char **))dlsym(dlHandle, ”Acme_Init");

...

acmeFuncs = acmeInit(&env, argc, argv);

45. F-3697
HAL : Details

Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 45 Security Level: Confidential A

46. F-3697
HAL : Details
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 46 Security Level: Confidential A

47. F-3697
Android Runtime
Handles the execution of Android applications
Almost entirely written from scratch by Google
Contains Dalvik, the virtual machine that executes every application that
you run on Android, and the core library for the Java runtime, coming from
Apache Harmony project
Also contains system daemons, init executable, basic binaries, etc.
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 47 Security Level: Confidential A
Libraries
Surface Manager Audio Manager SQLite
Open GL | ES FreeType WebKit
SGL SSL Bionic
Android Runtime
Core
Libraries
Dalvik
Virtual Machine

48. F-3697
Application Framework






Provides an API for developers to create applications
Exposes all the needed subsystems by providing an abstraction
Allows to easily use databases, create services, expose data to
other applications, receive system events, etc.
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 48 Security Level: Confidential A
Application Framework
Activity Manager Window Manager
Content
Provider
View System
Package Manager
Telephony
Manager
Resource
Manager
… Location Manager
Notification
Manager

49. F-3697
Application Framework
Activity manager
Manage the life cycle of applications
Content Provider
Share data between applications
Resource Manager
Manager non-code resource
Notification Manager
Display custom alerts in the status bar
Views System
A rich and extensible set, which can construct UI
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 49 Security Level: Confidential A

50. F-3697
Android Applications



AOSP also comes with a set of applications such as the phone
application, a browser, a contact management application, an
email client, etc.
However, the Google apps and the Android Market app aren’t
free software, so they are not available in AOSP. To obtain them,
you must contact Google and pass a compatibility test.
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 50 Security Level: Confidential A
Applications
Launcher2 Contacts Phone Browser ...

51. F-3697
Agenda
Intro
Android Architecture
Linux Kernel
Native Libraries
Android Runtime
Application Framework
Android Applications
Android Concepts ⊿
Key Concepts
Start-up Walkthrough
Layer Interaction
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 51 Security Level: Confidential A

52. F-3697
Android Key Concepts
APP Developer’s View
Component
Activities
Services
Broadcast Receivers
Content Providers
Intent

Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 52 Security Level: Confidential A

53. F-3697
Start-up Walkthrough
Runtime Walkthrough
It all starts with init…
Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 53 Security Level: Confidential A

54. F-3697
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

Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 54 Security Level: Confidential A

55. F-3697 Security Level: Confidential A Copyright © 2012 MStar Semiconductor, Inc. All rights reserved. 55