查看Introduction To EVS的源代码 Introduction To EVS 0

EVS: Exterior/Extended View System

•EVS is independent of Automotive OS framework. It can be deployed separately for fast rear-view camera or surround view displays in an Android-based IVI system.

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EVS Manager

Module name	android.automotive.evs.manager@1.0
Purpose	evs管理器，负责与HAL层的交互，实现HAL层的一些接口，例如openDisplay()，openCamera()等操作。
Register name	default
Service name	evs_manager
File location	/system/bin/android.automotive.evs.manager@1.0
Source location	/packages/services/Car/evs/manager/
EVS APP

Module name	evs_app
Purpose	 evs应用层，负责初始化操作，监听倒车状态，OpenGL 显示, 倒车UI更新等逻辑处理
Service name	evs_app
File location	/system/bin/evs_app
Source location	/packages/services/Car/evs
EVS HAL

Module name	android.hardware.automotive.evs@1.0
Purpose	An automotive HIDL Hardware Abstraction Layer (HAL) that provides for imagery capture and display very early in the Android boot process and continues functioning for the life of the system
Source location	/hardware/interfaces\automotive\evs\1.0
* 定义四个界面

IEvsCamera	Represents a single camera and is the primary interface for capturing images.
IEvsDisplay	information about the EVS display
IEvsEnumerator	Provides the mechanism for EVS camera discovery
IEvsCameraStream	 Implemented on client side to receive asynchronous video frame deliveries.
• EVS default driver

Module name	android.hardware.automotive.evs@1.0-service
Purpose	提供一个模拟倒车测试，显示静态图片模拟倒车；用于测试功能逻辑，不是真实的倒车
Register name	EvsEnumeratorHw
Service name	evs-hal-mock
File location	
/vendor/bin/hw/android.hardware.automotive.evs@1.0-service
Source location	/hardware/interfaces/automotive/evs/1.0/default
•SampleDriver:

Module name	android.hardware.automotive.evs@1.0-sample
Purpose	驱动层实现，基于v4l2实现的一个驱动Demo程序，供HAL层调用，Camera操作和display操作核心，涉及到摄像头设备操作和display设备操作。
Register name	EvsEnumeratorHw
Service name	evs_driver
File location	/system/bin/android.hardware.automotive.evs@1.0-sample
Source location	/packages/services/Car/evs/sampleDriver
Start video flow:
startVideoStream 展开源码
video capturing loop
collectFrames 展开源码


Discussion
Use EVS HAL as virtual camera for remote camera:
Effort: 修改 EvsEmulator 及实现 EvsCamera.   
pro: 
Well defined interfaces. Much simpler than Camera3 HAL
Server-Client 架构: Server有root权限操作camera, Client 透过binder 控制界面.
 Allow ISV to develope virtual camera application.
con:
boot time is longer, must wait EvsManager, Driver service, Gralloc service started before EVS_APP start.
EVS API is not so popular. 没有Camera3 的功能: 如 face detection, 3A 调整
Some of the features might not be usefull for our purpose.
Optimization counts on ISV. For example, minimum memcpy.




2. buffer memcpy

IEvsCamera sampleDriver copy V4L2 buffers to GraphicBuffer.
Camera V3.4 CmeraDevice: see also Mali Gralloc Tracing