车机系统开发流程（车机系统开发——Android Automotive）

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导读：Android Automotive介绍...

Android Automotive介绍

Android Automotive是⼀个基本的Android平台，它运⾏预安装的（车载信息娱乐）IVI系统，Android应⽤程序以及可选的第⼆⽅和第三⽅Android应⽤程序。

Android Automotive的硬件抽象层(HAL)为Android框架提供了一致的接口（无需考虑物理传输层）。此车载HAL是开发Android Automotive实现的接口。

系统集成商可以将特定于功能的平台HAL接口（如HVAC）与特定于技术的网络接口（如 CAN 总线）连接，以实现车载 HAL 模块。典型的实现可能包括运行专有实时操作系统(RTOS)的专用微控制器单元 (MCU) ，该微控制器单元用于CAN总线访问或类似操作，可通过串行链路连接到运行Android Automotive的CPU 。

AutoMotive整体架构

系统应用层

Android Automotive 为系统定制了一些专门适用车载系统的应用，以代替传统的手机应用模块。

系统应用层的Application都位于源码目录下：packages/apps/Car/

包含的应用如下

系统框架层

系统框架层提供了多个模块，来对Android Automotive 进行支持，最重要的有一个服务CarService (com.android.car) 。

系统框架层的模块都位于源码目录下：packages/services/Car/

CarService是一个类似Android系统中SystemSever的服务。它由一个服务启动，而里面又控制着数十个子模块服务。

CarService

CarService中CarService只作为服务的入口，具体的业务逻辑都在内部的子服务中处理，CarService的子服务如下。

CarService启动

CarService本质上是一个特殊的APP ，它编译后生成CarService.apk；在系统中，它是在/system/priv-app/CarService/CarService.apk

CarService在启动启动时，由SystemServer拉起

代码：frameworks/base/services/java/com/android/server/SystemServer.java

private static final String CAR_SERVICE_HELPER_SERVICE_CLASS = "com.android.internal.car.CarServiceHelperService"; private void startOtherServices() { mActivityManagerService.systemReady(() -> { if (mPackageManager.hasSystemFeature(PackageManager.FEATURE_AUTOMOTIVE)) { traceBeginAndSlog("StartCarServiceHelperService"); mSystemServiceManager.startService(CAR_SERVICE_HELPER_SERVICE_CLASS); traceEnd(); } }); }

代码：frameworks/opt/car/services/src/com/android/internal/car/CarServiceHelperService.java

private static final String CAR_SERVICE_INTERFACE = "android.car.ICar"; public class CarServiceHelperService extends SystemService { @Override public void onStart() { Intent intent = new Intent(); intent.setPackage("com.android.car"); intent.setAction(CAR_SERVICE_INTERFACE); if (!getContext().bindServiceAsUser(intent, mCarServiceConnection, Context.BIND_AUTO_CREATE, UserHandle.SYSTEM)) { Slog.wtf(TAG, "cannot start car service"); } System.loadLibrary("car-framework-service-jni"); } } SystemServer中ActivityManagerService.systemReady后会通过SystemServiceManager启动CarServiceHelperService CarServiceHelperService中绑定CarService 代码：packages/services/Car/service/AndroidManifest.xml <service android:name=".CarService" android:singleUser="true"> <intent-filter> <action android:name="android.car.ICar" /> </intent-filter> </service>

通过在CarService的AndroidManifest的配置，CarServiceHelperService可以通过包名和action的名称实现和CarService绑定。

Car API

Car API 是Android系统为汽车应用提供的一套SDK接口（Android Automotive Library）。

源代码位于packages/services/Car/car-lib目录下

Google官方的API文档在Android Q之后，也开始支持Android Automotive库。

链接地址： https://developer.android.google.cn/reference/android/car/package-summary

同CarService一样Car API 也提供的多个模块对应不同的功能调用。

硬件抽象层

硬件抽象层主要是提供了一个native服务android.hardware.automotive.vehicle@2.0-service ，负责处理车辆相关的业务。

硬件抽象层的模块位于源码目录下hardware/interfaces/automotive/

VehicleService

VehicleService是一个native服务，代码实现在目录hardware/interfaces/automotive/vehicle/2.0/default/impl/vhal_v2_0/

VehicleServices是Android Automotive在硬件抽象层的入口。它通过initrc启动。

代码：hardware/interfaces/automotive/vehicle/2.0/default/android.hardware.automotive.vehicle@2.0-service.rc

service vendor.vehicle-hal-2.0 /vendor/bin/hw/android.hardware.automotive.vehicle@2.0-service class hal user vehicle_network group system inet

VehicleHalManager

VehicleHalManager是Android Automotive在硬件抽象层的API接口。代码在目录

hardware/interfaces/automotive/vehicle/2.0/default/common/ 。

HAL接口语言

从硬件抽象层到系统框架层，也就是从VehicleService到CarService ，从Android O版本开始使用了一种新的HIDL接口。

HIDL 是用于指定 HAL 和其用户之间的接口的一种接口描述语言 (IDL) 。虽然从 Android 10 开始，HIDL 已废弃，Android 将在所有位置改用 AIDL 。但是Android Automotive的HIDL架构还保留着，直到Android 13才发生变化。

HIDL使用一种以.hal为后缀文件作为接口定义，在Android Automotive中硬件抽象层到系统框架层使用IVehicle.hal（代码路径：hardware/interfaces/automotive/vehicle/2.0/IVehicle.halhardware/interfaces/automotive/vehicle/2.0/IVehicle.hal）来定义。

代码：hardware/interfaces/automotive/vehicle/2.0/IVehicle.hal

package android.hardware.automotive.vehicle@2.0; import IVehicleCallback; interface IVehicle { /** * Returns a list of all property configurations supported by this vehicle * HAL. */ //返回这个vehicle hal支持的全部property属性 getAllPropConfigs() generates (vec<VehiclePropConfig> propConfigs); /** * Returns a list of property configurations for given properties. * * If requested VehicleProperty wasnt found it must return * StatusCode::INVALID_ARG, otherwise a list of vehicle property * configurations with StatusCode::OK */ getPropConfigs(vec<int32_t> props) generates (StatusCode status, vec<VehiclePropConfig> propConfigs); /** * Get a vehicle property value. * * For VehiclePropertyChangeMode::STATIC properties, this method must always * return the same value always. * For VehiclePropertyChangeMode::ON_CHANGE properties, it must return the * latest available value. * * Some properties like RADIO_PRESET requires to pass additional data in * GET request in VehiclePropValue object. * * If there is no data available yet, which can happen during initial stage, * this call must return immediately with an error code of * StatusCode::TRY_AGAIN. */ get(VehiclePropValue requestedPropValue) generates (StatusCode status, VehiclePropValue propValue); /** * Set a vehicle property value. * * Timestamp of data must be ignored for set operation. * * Setting some properties require having initial state available. If initial * data is not available yet this call must return StatusCode::TRY_AGAIN. * For a property with separate power control this call must return * StatusCode::NOT_AVAILABLE error if property is not powered on. */ set(VehiclePropValue propValue) generates (StatusCode status); /** * Subscribes to property events. * * Clients must be able to subscribe to multiple properties at a time * depending on data provided in options argument. * * @param listener This client must be called on appropriate event. * @param options List of options to subscribe. SubscribeOption contains * information such as property Id, area Id, sample rate, etc. */ subscribe(IVehicleCallback callback, vec<SubscribeOptions> options) generates (StatusCode status); /** * Unsubscribes from property events. * * If this client wasnt subscribed to the given property, this method * must return StatusCode::INVALID_ARG. */ unsubscribe(IVehicleCallback callback, int32_t propId) generates (StatusCode status); /** * Print out debugging state for the vehicle hal. * * The text must be in ASCII encoding only. * * Performance requirements: * * The HAL must return from this call in less than 10ms. This call must avoid * deadlocks, as it may be called at any point of operation. Any synchronization * primitives used (such as mutex locks or semaphores) must be acquired * with a timeout. * */ debugDump() generates (string s); };

IVehicle接口支持功能如下

update-makefiles.sh

通过update-makefiles.sh 可以创建编译HIDL文件的Android.bp 。

代码路径：hardware/interfaces/update-makefiles.sh

假设创建一个helloworld模块，在hardware/interfaces 下创建helloworld/1.0/IHelloWorld.hal：

package android.hardware.helloworld@1.0; interface IHelloWorld { justTest(string name); };

通过update-makefiles.sh就可以在对应package的目录下创建Android.bp：

// This file is autogenerated by hidl-gen -Landroidbp. hidl_interface { name: "android.hardware.helloworld@1.0", root: "android.hardware", vndk: { enabled: true, }, srcs: [ "IHelloWorld.hal", ], interfaces: [ "android.hidl.base@1.0", ], gen_java: true, }

name：模块的全名

root：包根目录

interfaces：编译过程中依赖的模块

gen_java：是否编译为Java 使用的接口

当然，还有其他的参数，例如gen_java_constants设为true 的时候会生成为Java 使用的Constants类。

全文概括了车机系统开发中的；Android Automotive原理架构解析；技术参考《车机开发手册》需要可以点击查看更多车载技术知识。

文末

车载HAL是汽车与车辆网络服务之间的接口定义（同时保护传入的数据）：

车载HAL与Android Automotive架构：

Car API：内有包含CarSensorManager在内的API 。位于/platform/packages/services/Car/car-lib CarService：位于 /platform/packages/services/Car/ 车载 HAL：用于定义OEM可以实现的车辆属性的接口。包含属性元数据（例如，车辆属性是否为int以及允许使用哪些更改模式）。位于hardware/libhardware/include/hardware/vehicle.h 。如需了解基本参考实现，请参阅 hardware/libhardware/modules/vehicle/（vehicle意思即车辆）