第一部分 Android Automative的整体架构
从这幅图中我们可以看出，Android Automative是在原先Android的系统架构上增加了一些与车相关的（图中虚线框中绿色背景的）模块。
包括：
Car App：包括OEM和第三方开发的App
Car API：提供给汽车App特有的接口
Car Service：系统中与车相关的服务
Vehicle Network Service：汽车的网络服务
Vehicle HAL：汽车的硬件抽象层描述
下面我们采取从上到下的顺序对主要模块做一些介绍。
Car App
packages/services/Car/car_product/build/car.mk 这个文件中列出了汽车系统中专有的模块：
BOARD_PLAT_PUBLIC_SEPOLICY_DIR += packages/services/Car/car_product/sepolicy/public
BOARD_PLAT_PRIVATE_SEPOLICY_DIR += packages/services/Car/car_product/sepolicy/private
# Automotive specific packages
PRODUCT_PACKAGES += \
CarService \
CarTrustAgentService \
CarDialerApp \
CarRadioApp \
OverviewApp \
CarLauncher \
CarLensPickerApp \
LocalMediaPlayer \
CarMediaApp \
CarMessengerApp \
CarHvacApp \
CarMapsPlaceholder \
CarLatinIME \
CarSettings \
CarUsbHandler \
android.car \
car-frameworks-service \
com.android.car.procfsinspector \
libcar-framework-service-jni \
# System Server components
PRODUCT_SYSTEM_SERVER_JARS += car-frameworks-service
# should add to BOOT_JARS only once
ifeq (,$(INCLUDED_ANDROID_CAR_TO_PRODUCT_BOOT_JARS))
PRODUCT_BOOT_JARS += \
android.car
INCLUDED_ANDROID_CAR_TO_PRODUCT_BOOT_JARS := yes
endif
这些app源码都位于packages/apps/Car/目录下，OEM厂商可以添加更多的App
Car API
packages/services/Car/car-lib/
开发汽车专有的App自然需要专有的API。这些API对于其他平台（例如手机和平板）通常是没有意义的。所以这些API没有包含在Android Framework SDK中，而是生成在android.car.jar中，源码编译时需要通过在Android.mk中添加LOCAL_JAVA_LIBRARIES += android.car 加入编译，Android Studio需要添加 android.car.jar加入编译，通过INCLUDED_ANDROID_CAR_TO_PRODUCT_BOOT_JARS 加入运行时。
下面这张大图列出了所有的Car API：
从这个图中我们可以看到Car API主要包括：
android.car：包含了与车相关的基本API。例如：车辆后视镜，门，座位，窗口等。
annotation：包含了两个注解。
app
menu：车辆应用菜单相关API。
cluster：仪表盘相关API。
render：渲染相关API。
content
pm：应用包相关API。
diagnostic：包含与汽车诊断相关的API。
hardware：车辆硬件相关API。
cabin：座舱相关API。
hvac：通风空调相关API。（hvac是Heating, ventilation and air conditioning的缩写）
property：属性相关API。
radio：收音机相关API。
input：输入相关API。
media：多媒体相关API。
navigation：导航相关API。
settings：设置相关API。
vms：汽车监测相关API，见下文。
CarService
源码：http://androidxref.com/9.0.0_r3/xref/packages/services/Car/
Android Automative中的Car Service集中在一个App中。可以想象，这个App需要非常高的权限，所以这是一个系统App。其Manifest开头如下：
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:androidprv="http://schemas.android.com/apk/prv/res/android"
package="com.android.car"
coreApp="true"
android:sharedUserId="android.uid.system">
android:sharedUserId属性"android.uid.system"使得这个应用具有系统权限
Car Service并非一个服务，而是一系列的服务这些服务都在ICarImpl.java构造函数中列了出来。
public ICarImpl(Context serviceContext, IVehicle vehicle, SystemInterface systemInterface,
CanBusErrorNotifier errorNotifier, String vehicleInterfaceName) {
mContext = serviceContext;
mSystemInterface = systemInterface;
mHal = new VehicleHal(vehicle);
mVehicleInterfaceName = vehicleInterfaceName;
mSystemActivityMonitoringService = new SystemActivityMonitoringService(serviceContext);
mCarPowerManagementService = new CarPowerManagementService(mContext, mHal.getPowerHal(),
systemInterface);
mCarPropertyService = new CarPropertyService(serviceContext, mHal.getPropertyHal());
mCarDrivingStateService = new CarDrivingStateService(serviceContext, mCarPropertyService);
mCarUXRestrictionsService = new CarUxRestrictionsManagerService(serviceContext,
mCarDrivingStateService, mCarPropertyService);
mCarPackageManagerService = new CarPackageManagerService(serviceContext,
mCarUXRestrictionsService,
mSystemActivityMonitoringService);
mCarInputService = new CarInputService(serviceContext, mHal.getInputHal());
mCarProjectionService = new CarProjectionService(serviceContext, mCarInputService);
mGarageModeService = new GarageModeService(mContext, mCarPowerManagementService);
mCarLocationService = new CarLocationService(mContext, mCarPowerManagementService,
mCarPropertyService);
mAppFocusService = new AppFocusService(serviceContext, mSystemActivityMonitoringService);
mCarAudioService = new CarAudioService(serviceContext);
mCarNightService = new CarNightService(serviceContext, mCarPropertyService);
mInstrumentClusterService = new InstrumentClusterService(serviceContext,
mAppFocusService, mCarInputService);
mSystemStateControllerService = new SystemStateControllerService(serviceContext,
mCarPowerManagementService, mCarAudioService, this);
mPerUserCarServiceHelper = new PerUserCarServiceHelper(serviceContext);
mCarBluetoothService = new CarBluetoothService(serviceContext, mCarPropertyService,
mPerUserCarServiceHelper, mCarUXRestrictionsService);
mVmsSubscriberService = new VmsSubscriberService(serviceContext, mHal.getVmsHal());
mVmsPublisherService = new VmsPublisherService(serviceContext, mHal.getVmsHal());
mCarDiagnosticService = new CarDiagnosticService(serviceContext, mHal.getDiagnosticHal());
mCarStorageMonitoringService = new CarStorageMonitoringService(serviceContext,
systemInterface);
mCarConfigurationService =
new CarConfigurationService(serviceContext, new JsonReaderImpl());
mUserManagerHelper = new CarUserManagerHelper(serviceContext);
CarTool
packages/services/Car/tools
略
EVS
packages/services/Car/evs/
略
ODB2
packages/services/Car/obd2-lib/
略
Vehicle Network Service
略
HAL
略
第二部分 CarService启动流程
SystemServer启动CarService
SystemServer里会启动CarServiceHelperService，如下：
if (mPackageManager.hasSystemFeature(PackageManager.FEATURE_AUTOMOTIVE)) {
traceBeginAndSlog("StartCarServiceHelperService");
mSystemServiceManager.startService(CarServiceHelperService.class);
traceEnd();
}
而CarServiceHelperService.onStart()会bind到CarService，如下：
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");
}
注意：这里用的是bindService方式，mCarServiceConnection是ServiceConnection类对象，它能监听目标Service的状态，当目标Service所在进程异常退出时，会导致其onServiceDisconnected()方法被调用
CarService启动其他service
CarService.onCreate()里会创建ICarImpl的实例，并调用ICarImpl.init()方法；
Log.i(CarLog.TAG_SERVICE, "Service onCreate");
mCanBusErrorNotifier = new CanBusErrorNotifier(this /* context */);
mVehicle = getVehicle();
if (mVehicle == null) {
throw new IllegalStateException("Vehicle HAL service is not available.");
}
try {
mVehicleInterfaceName = mVehicle.interfaceDescriptor();
} catch (RemoteException e) {
throw new IllegalStateException("Unable to get Vehicle HAL interface descriptor", e);
}
Log.i(CarLog.TAG_SERVICE, "Connected to " + mVehicleInterfaceName);
mICarImpl = new ICarImpl(this, mVehicle, SystemInterface.getDefault(this),
mCanBusErrorNotifier);
mICarImpl.init();
SystemProperties.set("boot.car_service_created", "1");
linkToDeath(mVehicle, mVehicleDeathRecipient);
super.onCreate();
而ICarImpl.init()里会启动一大堆Service，其中就包括InstrumentClusterService，如下
// Be careful with order. Service depending on other service should be inited later.
List<CarServiceBase> allServices = new ArrayList<>(Arrays.asList(
mSystemActivityMonitoringService,
mCarPowerManagementService,
mCarSensorService,
mCarPackageManagerService,
mCarInputService,
mGarageModeService,
mCarInfoService,
mAppFocusService,
mCarAudioService,
mCarCabinService,
mCarHvacService,
mCarRadioService,
mCarNightService,
mInstrumentClusterService,
mCarProjectionService,
mSystemStateControllerService,
mCarVendorExtensionService,
mCarBluetoothService,
mCarDiagnosticService,
mPerUserCarServiceHelper
));
注意服务启动顺序，依赖于其他服务的service靠后初始化。
Car App
通过Car.createCar 获得car，再通过car.getCarManager获得service
例如，CarAudioManager carAudioManager = car.getCarManager(Car.AUDIO_SERVICE);
app通过各种CarXXManager获取服务然后注册Listener或者调用接口。
system.img
android.car编译并加入PRODUCT_BOOT_JARS,存储路径/system/framework/android.car.jar
CarService编译后路径为 /system/priv-app/CarService
其他app编译后路径,例如/system/priv-app/CarLauncher，/system/priv-app/CarMediaApp
参考:
https://yq.aliyun.com/articles/610105?utm_content=m_1000006763
https://www.jianshu.com/p/dacc21e2b32e
https://www.jianshu.com/p/2c3659800fbc makefile PRODUCT_BOOT_JARS 处理流程及实例
