if (getPackageManager().hasSystemFeature(PackageManager.FEATURE_AUTOMOTIVE)) {
    .....
}

//packages/apps/SettingsIntelligence/src/com/android/settings/intelligence/suggestions/eligibility/AutomotiveEligibilityChecker.java
    public static boolean isEligible(Context context, String id, ResolveInfo info) {
        PackageManager packageManager = context.getPackageManager();
        //是否支持车载功能
        boolean isAutomotive = packageManager.hasSystemFeature(PackageManager.FEATURE_AUTOMOTIVE);
        //是否有车载功能支持的资格
        boolean isAutomotiveEligible =
                info.activityInfo.metaData.getBoolean(META_DATA_AUTOMOTIVE_ELIGIBLE, false);
        if (isAutomotive) {
            if (!isAutomotiveEligible) {
                Log.i(TAG, "Suggestion is ineligible for FEATURE_AUTOMOTIVE: " + id);
            }
            return isAutomotiveEligible;
        }
        return true;
    }

//frameworks/base/services/core/java/com/android/server/pm/PackageManagerService.java
    @GuardedBy("mAvailableFeatures")
    final ArrayMap<String, FeatureInfo> mAvailableFeatures;

    @Override
    public boolean hasSystemFeature(String name, int version) {
        // allow instant applications
        synchronized (mAvailableFeatures) {
            final FeatureInfo feat = mAvailableFeatures.get(name);
            if (feat == null) {
                return false;
            } else {
                return feat.version >= version;
            }
        }
    }

//frameworks/native/data/etc/car_core_hardware.xml
<permissions>
    <!-- Feature to specify if the device is a car -->
    <feature name="android.hardware.type.automotive" />
    .....
</permission>

//frameworks/native/data/etc/android.hardware.type.automotive.xml
<!-- These features determine that the device running android is a car. -->
<permissions>
    <feature name="android.hardware.type.automotive" />
</permissions>

//packages/apps/Car/Hvac/src/com/android/car/hvac/HvacController.java
  private Object mHvacManagerReady = new Object();

 @Override
    public void onCreate() {
        super.onCreate();
        if (getPackageManager().hasSystemFeature(PackageManager.FEATURE_AUTOMOTIVE)) {
            if (SystemProperties.getBoolean(DEMO_MODE_PROPERTY, false)) {
                IBinder binder = (new LocalHvacPropertyService()).getCarPropertyService();
                initHvacManager(new CarHvacManager(binder, this, new Handler()));
                return;
            }
            //创建Car实例，即new Car对象
            mCarApiClient = Car.createCar(this, mCarConnectionCallback);
            //connect连接，调用startCarService启动CarService
            mCarApiClient.connect();
        }
    }

    private final CarConnectionCallback mCarConnectionCallback =
            new CarConnectionCallback() {
                @Override
                public void onConnected(Car car) {
                    synchronized (mHvacManagerReady) {
                        try {
                            //getCarManager获取manager
                            //在获取到CarHvacManager后，可以直接调用CarHvacManager提供的接口
                            //例如mHvacManager.getPropertyList();
                            initHvacManager((CarHvacManager) mCarApiClient.getCarManager(
                                    android.car.Car.HVAC_SERVICE));
                            mHvacManagerReady.notifyAll();
                        } catch (CarNotConnectedException e) {
                            Log.e(TAG, "Car not connected in onServiceConnected");
                        }
                    }
                }

                @Override
                public void onDisconnected(Car car) {
                }
            };

    private void initHvacManager(CarHvacManager carHvacManager) {
        mHvacManager = carHvacManager;
        List<CarPropertyConfig> properties = null;
        try {
            properties = mHvacManager.getPropertyList();
            mPolicy = new HvacPolicy(HvacController.this, properties);
            //注册回调
            mHvacManager.registerCallback(mHardwareCallback);
        } catch (android.car.CarNotConnectedException e) {
            Log.e(TAG, "Car not connected in HVAC");
        }
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        if (mHvacManager != null) {
            //取消注册回调
            mHvacManager.unregisterCallback(mHardwareCallback);
        }
        if (mCarApiClient != null) {
            mCarApiClient.disconnect();
        }
    }

    //接收处理callback消息
    private final CarHvacManager.CarHvacEventCallback mHardwareCallback =
            new CarHvacManager.CarHvacEventCallback() {
                @Override
                public void onChangeEvent(final CarPropertyValue val) {
                    int areaId = val.getAreaId();
                    switch (val.getPropertyId()) {
                        case CarHvacManager.ID_ZONED_AC_ON:
                            handleAcStateUpdate(getValue(val));
                            break;
                        case CarHvacManager.ID_ZONED_FAN_DIRECTION:
                            handleFanPositionUpdate(areaId, getValue(val));
                        .....
                        default:
                            if (Log.isLoggable(TAG, Log.DEBUG)) {
                                Log.d(TAG, "Unhandled HVAC event, id: " + val.getPropertyId());
                            }
                    }
                }

                @Override
                public void onErrorEvent(final int propertyId, final int zone) {
                }
            };

//packages/apps/Car/Radio/src/com/android/car/radio/platform/RadioTunerExt.java
    RadioTunerExt(Context context) {
        //创建Car实例，即new Car对象
        mCar = Car.createCar(context, mCarServiceConnection);
        //connect连接，调用startCarService启动CarService
        mCar.connect();
    }

    private final ServiceConnection mCarServiceConnection = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
            synchronized (mLock) {
                try {
                    //getCarManager获取manager
                    mCarAudioManager = (CarAudioManager)mCar.getCarManager(Car.AUDIO_SERVICE);
                    if (mPendingMuteOperation != null) {
                        boolean mute = mPendingMuteOperation;
                        mPendingMuteOperation = null;
                        Log.i(TAG, "Car connected, executing postponed operation: "
                                + (mute ? "mute" : "unmute"));
                        setMuted(mute);
                    }
        .....

.
├── Android.mk
├── apicheck.mk
├── apicheck_msg_current.txt
├── apicheck_msg_last.txt
├── car-cluster-logging-renderer    //LoggingClusterRenderingService继承InstrumentClusterRenderingService
├── car-default-input-service   //按键消息处理
├── car-lib         //提供给汽车App特有的接口，许多定制的模块都在这里实现，包括Sensor,HVAC,Cabin,ActiveParkingAssiance,Diagnostic,Vendor等
├── car-maps-placeholder    //地图软件相关
├── car_product         //系统编译相关
├── car-support-lib     //android.support.car
├── car-systemtest-lib  //系统测试相关
├── car-usb-handler     //开机自启，用于管理车机USB
├── CleanSpec.mk
├── evs  
├── obd2-lib
├── PREUPLOAD.cfg
├── procfs-inspector
├── service    //com.android.car是一个后台运行的组件，可以长时间运行并且不需要和用户去交互的，这里即使应用被销毁，它也可以正常工作
├── tests
├── tools   //是一系列的工具，要提到的是里面的emulator，测试需要用到的。python写的，通过adb可以连接vehicleHal的工具，用于模拟测试
├── TrustAgent
└── vehicle-hal-support-lib

//packages/services/Car/car_product/build/car.mk
# Automotive specific packages
PRODUCT_PACKAGES += \
    CarService \
    CarTrustAgentService \
    CarDialerApp \                      # 电话应用，包含拨号键盘、通话记录等
    CarRadioApp \                       # 收音机应用
    OverviewApp \
    CarLauncher \
    CarLensPickerApp \                  # 活动窗口选择应用（Launcher）
    LocalMediaPlayer \                  # 提供本地播放服务的应用
    CarMediaApp \                       # 媒体应用，包含播放界面等
    CarMessengerApp \                   # 消息管理应用，包含消息及TTS相关功能
    CarHvacApp \                        # 空调应用，空调显示及操作界面
    CarMapsPlaceholder \
    CarLatinIME \                       # 输入法应用
    CarSettings \                       # 设置应用
    CarUsbHandler \
    android.car \
    car-frameworks-service \
    com.android.car.procfsinspector \
    libcar-framework-service-jni \
....
PRODUCT_PACKAGES += \
    Bluetooth \
    OneTimeInitializer \
    Provision \
    SystemUI \
    SystemUpdater                       # 系统升级应用

//packages/services/Car/car-lib/src/android/car/input/CarInputHandlingService.java
    private class InputBinder extends ICarInputListener.Stub {
        private final EventHandler mEventHandler;

        InputBinder() {
            mEventHandler = new EventHandler(CarInputHandlingService.this);
        }

        @Override
        public void onKeyEvent(KeyEvent keyEvent, int targetDisplay) throws RemoteException {
            mEventHandler.doKeyEvent(keyEvent, targetDisplay);
        }
    }

//packages/services/Car/service/src/com/android/car/CarInputService.java
    private final ServiceConnection mInputServiceConnection = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName name, IBinder binder) {
            if (DBG) {
                Log.d(CarLog.TAG_INPUT, "onServiceConnected, name: "
                        + name + ", binder: " + binder);
            }
            mCarInputListener = ICarInputListener.Stub.asInterface(binder);

            try {
                binder.linkToDeath(() -> CarServiceUtils.runOnMainSync(() -> {
                    Log.w(CarLog.TAG_INPUT, "Input service died. Trying to rebind...");
                    mCarInputListener = null;
                    // Try to rebind with input service.
                    mCarInputListenerBound = bindCarInputService();
                }), 0);
            } catch (RemoteException e) {
                Log.e(CarLog.TAG_INPUT, e.getMessage(), e);
            }
        }

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

    @SuppressWarnings("unchecked")
    public SystemService startService(String className) {
        ....
        return startService(serviceClass);
    }

    public <T extends SystemService> T startService(Class<T> serviceClass) {
        ...
        startService(service);
        ...
    }

    public void startService(@NonNull final SystemService service) {
        ......
        try {
            service.onStart();
            ...
        }

    //这就是系统中和汽车相关的核心服务CarService，相关源代码在packages/services/Car/service目录下
    private static final String CAR_SERVICE_INTERFACE = "android.car.ICar";

    @Override
    public void onStart() {
        Intent intent = new Intent();
        intent.setPackage("com.android.car");  //绑定包名，设置广播仅对该包有效
        //绑定action，表明想要启动能够响应设置的这个action的活动，并在清单文件AndroidManifest.xml中设置action属性
        intent.setAction(CAR_SERVICE_INTERFACE);
        //绑定后回调
        if (!getContext().bindServiceAsUser(intent, mCarServiceConnection, Context.BIND_AUTO_CREATE,
                UserHandle.SYSTEM)) {
            Slog.wtf(TAG, "cannot start car service");
        }
        System.loadLibrary("car-framework-service-jni");
    }

//packages/services/Car/service/AndroidManifest.xml
<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"> 
        ......
<application android:label="Car service"
                 android:directBootAware="true"
                 android:allowBackup="false"
                 android:persistent="true">
        <service android:name=".CarService"
                android:singleUser="true">
            <intent-filter>
                <action android:name="android.car.ICar" />
            </intent-filter>
        </service>
        <service android:name=".PerUserCarService" android:exported="false" />
    </application>

    @Nullable
    private static IVehicle getVehicle() {
        try {
            //该service启动文件hardware/interfaces/automotive/vehicle/2.0/default/android.hardware.automotive.vehicle@2.0-service.rc
            return android.hardware.automotive.vehicle.V2_0.IVehicle.getService();
        } ....
        return null;
    }

    @Override
    public void onCreate() {
        Log.i(CarLog.TAG_SERVICE, "Service onCreate");
        //获取hal层的Vehicle service
        mVehicle = getVehicle();

        //创建ICarImpl实例
        mICarImpl = new ICarImpl(this,
                mVehicle,
                SystemInterface.Builder.defaultSystemInterface(this).build(),
                mCanBusErrorNotifier,
                mVehicleInterfaceName);
        //然后调用ICarImpl的init初始化方法
        mICarImpl.init();
        //设置boot.car_service_created属性
        SystemProperties.set("boot.car_service_created", "1");

        linkToDeath(mVehicle, mVehicleDeathRecipient);
        //最后将该service注册到ServiceManager
        ServiceManager.addService("car_service", mICarImpl);
        super.onCreate();
    }

//packages/services/Car/service/src/com/android/car/ICarImpl.java
    private final VehicleHal mHal;
    //构造函数启动一大堆服务
    public ICarImpl(Context serviceContext, IVehicle vehicle, SystemInterface systemInterface,
            CanBusErrorNotifier errorNotifier, String vehicleInterfaceName) {
        mContext = serviceContext;
        mSystemInterface = systemInterface;
        //创建VehicleHal对象
        mHal = new VehicleHal(vehicle);
        mVehicleInterfaceName = vehicleInterfaceName;
        mSystemActivityMonitoringService = new SystemActivityMonitoringService(serviceContext);
        mCarPowerManagementService = new CarPowerManagementService(mContext, mHal.getPowerHal(),
                systemInterface);
        mCarPropertyService = new CarPropertyService(serviceContext, mHal.getPropertyHal());
        .....
        //InstrumentClusterService service启动
        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);

        //注意排序，service存在依赖
        List<CarServiceBase> allServices = new ArrayList<>();
        allServices.add(mSystemActivityMonitoringService);
        allServices.add(mCarPowerManagementService);
        allServices.add(mCarPropertyService);
        allServices.add(mCarDrivingStateService);
        allServices.add(mCarUXRestrictionsService);
        allServices.add(mCarPackageManagerService);
        allServices.add(mCarInputService);
        allServices.add(mCarLocationService);
        allServices.add(mGarageModeService);
        allServices.add(mAppFocusService);
        allServices.add(mCarAudioService);
        allServices.add(mCarNightService);
        allServices.add(mInstrumentClusterService);
        allServices.add(mCarProjectionService);
        allServices.add(mSystemStateControllerService);
        // allServices.add(mCarBluetoothService);
        allServices.add(mCarDiagnosticService);
        allServices.add(mPerUserCarServiceHelper);
        allServices.add(mCarStorageMonitoringService);
        allServices.add(mCarConfigurationService);
        allServices.add(mVmsSubscriberService);
        allServices.add(mVmsPublisherService);

        if (mUserManagerHelper.isHeadlessSystemUser()) {
            mCarUserService = new CarUserService(serviceContext, mUserManagerHelper);
            allServices.add(mCarUserService);
        }

        mAllServices = allServices.toArray(new CarServiceBase[allServices.size()]);
    }

    @MainThread
    void init() {
        traceBegin("VehicleHal.init");
        mHal.init();
        traceEnd();
        traceBegin("CarService.initAllServices");
        //启动的所有服务遍历调用init初始化（各个都继承了CarServiceBase）
        for (CarServiceBase service : mAllServices) {
            service.init();
        }
        traceEnd();
    }

//packages/services/Car/service/src/com/android/car/CarService.java
    @Override
    public IBinder onBind(Intent intent) {
        return mICarImpl;
    }

    @Override
    public void onDestroy() {
        Log.i(CarLog.TAG_SERVICE, "Service onDestroy");
        mICarImpl.release();
        mCanBusErrorNotifier.removeFailureReport(this);

        if (mVehicle != null) {
            try {
                mVehicle.unlinkToDeath(mVehicleDeathRecipient);
                mVehicle = null;
            } catch (RemoteException e) {
                // Ignore errors on shutdown path.
            }
        }

        super.onDestroy();
    }

//frameworks/opt/car/services/src/com/android/internal/car/CarServiceHelperService.java
private static final String CAR_SERVICE_INTERFACE = "android.car.ICar";
private IBinder mCarService;
private final ICarServiceHelperImpl mHelper = new ICarServiceHelperImpl();

private final ServiceConnection mCarServiceConnection = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName componentName, IBinder iBinder) {
            Slog.i(TAG, "**CarService connected**");
            //1. 返回的ICarImpl被保存在了CarServiceHelperService的mCarService
            mCarService = iBinder;
            // Cannot depend on ICar which is defined in CarService, so handle binder call directly
            // instead. 
            // void setCarServiceHelper(in IBinder helper)
            Parcel data = Parcel.obtain();
            data.writeInterfaceToken(CAR_SERVICE_INTERFACE);
            //将ICarServiceHelperImpl类型的对象作为数据跨进程传递
            data.writeStrongBinder(mHelper.asBinder());
            try {
                //2.跨进程传输
                //对端是mCarService即ICarImpl，调用binder的transact进行跨进程通信
                //其code代表需要调用的对端方法，data为携带的传输数据
                //FIRST_CALL_TRANSACTION  = 0x00000001，即调用对端ICar.aidl中定义的第一个方法setCarServiceHelper
                mCarService.transact(IBinder.FIRST_CALL_TRANSACTION, // setCarServiceHelper
                        data, null, Binder.FLAG_ONEWAY);
            } catch (RemoteException e) {
                Slog.w(TAG, "RemoteException from car service", e);
                handleCarServiceCrash();
            }
        }

        @Override 
        public void onServiceDisconnected(ComponentName componentName) {
            handleCarServiceCrash();
        }
    };

    @Override
    public void setCarServiceHelper(IBinder helper) {
        int uid = Binder.getCallingUid();
        if (uid != Process.SYSTEM_UID) {
            throw new SecurityException("Only allowed from system");
        }
        synchronized (this) {
            //将ICarServiceHelper的代理端保存在ICarImpl内部mICarServiceHelper
            mICarServiceHelper = ICarServiceHelper.Stub.asInterface(helper);
            //同时也传给了SystemInterface
            //此时他们有能力跨进程访问CarServiceHelperService
            mSystemInterface.setCarServiceHelper(mICarServiceHelper);
        }
    }