Introduction To EVS
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.
- 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。 |
| Register name | |
| 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
