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
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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

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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

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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.

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Agenda
 Intro
 Android Architecture ⊿
 Linux Kernel
 Android Runtime
 Android Concepts
 Key Concepts

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Android Architecture
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
Linux Kernel
Driver
Management
Shared Memory
Driver
Audio Driver

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Linux Kernel
 Android vs. Linux Distributions
X No native window GUI system (GNOME/KDE)
X No glibc support
X Does not include the full set of standard Linux utilities
 Standard Linux Kernel (version 2.6+)
X Patches of “kernel enhancements” to support Android
Linux Kernel
Driver
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
Linux Kernel
Driver
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
Linux Kernel
Driver
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. "
Linux Kernel
Driver
Management
Shared Memory
Driver
Audio Driver

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Binder in Action
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
Linux Kernel
Driver
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
Linux Kernel
Driver
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
Linux Kernel
Driver
Management
Shared Memory
Driver
Audio Driver

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Android PM in Action
App A Power Manager PM Driver
NewWake Lock
PARTIAL
CreateWake Lock
Release
Release
Turn Off
CPU
Turn Off
LCD

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Android PM
 How to use Android PM from App developer’s view?
 android.os.PowerManager
 Use wake locks carefully!
 userActivity(long when, …)
Linux Kernel
Driver
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
Linux Kernel
Driver
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
Libraries
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.
Libraries
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
Libraries
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
Libraries
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’”);

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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

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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
Libraries
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
Libraries
SGL SSL Bionic
Android Runtime
Core
Libraries
Dalvik
Virtual Machine

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Function Libraries
 Open GL | ES
 3D graphics engine
 An implementation based on OpenGL ES 1.0 APIs
Libraries
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
Libraries
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
Libraries
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
Libraries
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
Libraries
SGL SSL Bionic
Android Runtime
Core
Libraries
Dalvik
Virtual Machine

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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
Libraries
Open GL | ES Audio Manager WebKit
SGL SSL Bionic
Android Runtime
Core
Libraries
Dalvik
Virtual Machine

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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)
Libraries
SGL SSL Bionic
Android Runtime
Core
Libraries
Dalvik
Virtual Machine

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Typical Graphical Stacks

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Surface Flinger

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Native Services
 Audio Flinger
 Manages all audio output devices
 Processes multiple audio streams into PCM audio out paths
 Handles audio routing to various outputs
Libraries
SGL SSL Bionic
Android Runtime
Core
Libraries
Dalvik
Virtual Machine

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Audio Flinger

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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
Libraries
SGL SSL Bionic
Android Runtime
Core
Libraries
Dalvik
Virtual Machine
Linux Kernel
Driver
Management
Shared Memory
Driver
Audio Driver

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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
Linux Kernel
Driver
Management
Shared Memory
Driver
Audio Driver
Bluetooth RIL ...

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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
Linux Kernel
Driver
Management
Shared Memory
Driver
Audio Driver
Bluetooth RIL ...

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HAL : Details
 Loading and Interfacing Methods
 dlopen() - loading through HAL
 Linker-loaded .so files
 Hardcoded dlopen()s
 Sockets
 Sysfs entries
 /dev nodes
 D-Bus

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HAL : Details
 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);

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HAL : Details
 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);

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HAL : Details

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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.
Libraries
Surface Manager Audio Manager SQLite
SGL SSL Bionic
Android Runtime
Core
Libraries
Dalvik
Virtual Machine

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 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.
Activity Manager Window Manager Content
Provider View System
Package Manager Telephony
Manager
Resource
Manager …
Location Manager
Notification
Manager

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 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

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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.
Applications
Launcher2 Contacts Phone Browser ...

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Agenda
 Intro
 Android Architecture
 Linux Kernel
 Android Runtime
 Android Concepts ⊿
 Key Concepts

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Android Key Concepts
 APP Developer’s View
 Component
 Activities
 Services
 Broadcast Receivers
 Content Providers
 Intent

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Start-up Walkthrough
 Runtime Walkthrough
 It all starts with init…

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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

BSP Developer Must Know about Android.pdf

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