Android Framework系列—CarPower电源管理

智能座舱通常包括中控系统、仪表系统、IVI系统 、后排娱乐、HUD、车联网等。这些系统需要由汽车电源进行供电。由于汽车自身的特殊供电环境（相比手机方便的充电环境，汽车的蓄电池如果没有电是需要专业人士操作的），其电源状态会比较复杂，既要满足车内的座舱系统启动足够快，又要保证汽车蓄电池的可考性，所以出了开机（on）、关机（off）外，会多出来一些电源状态（Suspend、STR、SLEEP等等）

所以，一般来说软件系统是需要一个专门的电源管理模块的。

CarPower电源管理

Android Automotive（基于Android平台的车载信息娱乐系统）提供了CarPower模块用于管理电源状态。CarPower Service属于CarService，在SystemSever的startOtherService阶段启动。

CarPower Service根据来自于 Vehicle HAL（Hal层服务）的电源状态通知，进行相关的逻辑判断后，应用电源策略（简单理解成告知某些服务Enable 或者Disable）、发送状态通知给它自身的监听者、回复（Report）VehcileHAL处理结果。
Vehicle HAL的电源状态一般来讲是来自于MCU的（can通信 或者以太网通信，具体形式由Vehicle HAL和相关供应商决定）。电源状态变化时，MCU一般会拉低或者拉高某个引脚，然后通知事件给VehicleHAL，VehicleHAL再通过PropertyEvent通知给CarPower Service。Android系统处理完电源状态后（有超时要求），再由VehiclHAL告知MCU,MCU在对某个引脚进行相关操作。

CarPower电源管理的开机流程

下面以Android车载系统开机为例。说明一下CarPower模块的开机时序。代码基于Android12.

• CarPower服务启动：Android系统开机上电，在systemServer中启动CarService。

// frameworks/base/services/java/com/android/server/SystemServer.java/*** Starts a miscellaneous grab bag of stuff that has yet to be refactored and organized.*/
private void startOtherServices(@NonNull TimingsTraceAndSlog t) {if (mPackageManager.hasSystemFeature(PackageManager.FEATURE_AUTOMOTIVE)) {t.traceBegin("StartCarServiceHelperService");final SystemService cshs = mSystemServiceManager.startService(CAR_SERVICE_HELPER_SERVICE_CLASS);if (cshs instanceof Dumpable) {mDumper.addDumpable((Dumpable) cshs);}if (cshs instanceof DevicePolicySafetyChecker) {dpms.setDevicePolicySafetyChecker((DevicePolicySafetyChecker) cshs);}t.traceEnd();}}// frameworks/opt/car/services/src/com/android/internal/car/CarServiceHelperService.java
public void onStart() {EventLog.writeEvent(EventLogTags.CAR_HELPER_START, mHalEnabled ? 1 : 0);IntentFilter filter = new IntentFilter(Intent.ACTION_REBOOT);filter.addAction(Intent.ACTION_SHUTDOWN);mContext.registerReceiverForAllUsers(mShutdownEventReceiver, filter, null, null);mCarWatchdogDaemonHelper.addOnConnectionChangeListener(mConnectionListener);mCarWatchdogDaemonHelper.connect();// 启动了CarService------------------------------------------Intent intent = new Intent();intent.setPackage("com.android.car");intent.setAction(ICarConstants.CAR_SERVICE_INTERFACE);if (!mContext.bindServiceAsUser(intent, mCarServiceConnection, Context.BIND_AUTO_CREATE,UserHandle.SYSTEM)) {Slog.wtf(TAG, "cannot start car service");}loadNativeLibrary();
}

• CarService启动后会创建CarPower实例。

<!-- packages/services/Car/service/AndroidManifest.xml -->
<application android:label="@string/app_title"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>

// packages/services/Car/service/src/com/android/car/ICarImpl.java
public class ICarImpl extends ICar.Stub {public ICarImpl(Context serviceContext, IVehicle vehicle, SystemInterface systemInterface,CanBusErrorNotifier errorNotifier, String vehicleInterfaceName) {this(serviceContext, vehicle, systemInterface, errorNotifier, vehicleInterfaceName,/* carUserService= */ null, /* carWatchdogService= */ null);}@VisibleForTestingICarImpl(Context serviceContext, IVehicle vehicle, SystemInterface systemInterface,CanBusErrorNotifier errorNotifier, String vehicleInterfaceName,@Nullable CarUserService carUserService,@Nullable CarWatchdogService carWatchdogService) {mContext = serviceContext;mSystemInterface = systemInterface;mHal = new VehicleHal(serviceContext, vehicle);// Do this before any other service components to allow feature check. It should work// even without init. For that, vhal get is retried as it can be too early.VehiclePropValue disabledOptionalFeatureValue = mHal.getIfAvailableOrFailForEarlyStage(VehicleProperty.DISABLED_OPTIONAL_FEATURES, INITIAL_VHAL_GET_RETRY);String[] disabledFeaturesFromVhal = null;if (disabledOptionalFeatureValue != null) {String disabledFeatures = disabledOptionalFeatureValue.value.stringValue;if (disabledFeatures != null && !disabledFeatures.isEmpty()) {disabledFeaturesFromVhal = disabledFeatures.split(",");}}if (disabledFeaturesFromVhal == null) {disabledFeaturesFromVhal = new String[0];}Resources res = mContext.getResources();String[] defaultEnabledFeatures = res.getStringArray(R.array.config_allowed_optional_car_features);mFeatureController = new CarFeatureController(serviceContext, defaultEnabledFeatures,disabledFeaturesFromVhal , mSystemInterface.getSystemCarDir());CarLocalServices.addService(CarFeatureController.class, mFeatureController);mVehicleInterfaceName = vehicleInterfaceName;mUserManagerHelper = new CarUserManagerHelper(serviceContext);if (carUserService != null) {mCarUserService = carUserService;} else {UserManager userManager =(UserManager) serviceContext.getSystemService(Context.USER_SERVICE);int maxRunningUsers = res.getInteger(com.android.internal.R.integer.config_multiuserMaxRunningUsers);mCarUserService = new CarUserService(serviceContext, mHal.getUserHal(),mUserManagerHelper, userManager, ActivityManager.getService(), maxRunningUsers);}mCarOccupantZoneService = new CarOccupantZoneService(serviceContext);mSystemActivityMonitoringService = new SystemActivityMonitoringService(serviceContext);// 这里创建了CarPower服务实例-----------------------------------------------------------mCarPowerManagementService = new CarPowerManagementService(mContext, mHal.getPowerHal(),systemInterface, mCarUserService);if (mFeatureController.isFeatureEnabled(CarFeatures.FEATURE_CAR_USER_NOTICE_SERVICE)) {mCarUserNoticeService = new CarUserNoticeService(serviceContext);} else {mCarUserNoticeService = null;}mCarPropertyService = new CarPropertyService(serviceContext, mHal.getPropertyHal());mCarDrivingStateService = new CarDrivingStateService(serviceContext, mCarPropertyService);mCarUXRestrictionsService = new CarUxRestrictionsManagerService(serviceContext,mCarDrivingStateService, mCarPropertyService);if (mFeatureController.isFeatureEnabled(Car.OCCUPANT_AWARENESS_SERVICE)) {mOccupantAwarenessService = new OccupantAwarenessService(serviceContext);} else {mOccupantAwarenessService = null;}mCarPackageManagerService = new CarPackageManagerService(serviceContext,mCarUXRestrictionsService,mSystemActivityMonitoringService,mCarUserService);mPerUserCarServiceHelper = new PerUserCarServiceHelper(serviceContext, mCarUserService);mCarBluetoothService = new CarBluetoothService(serviceContext, mPerUserCarServiceHelper);mCarInputService = new CarInputService(serviceContext, mHal.getInputHal(), mCarUserService);mCarProjectionService = new CarProjectionService(serviceContext, null /* handler */, mCarInputService, mCarBluetoothService);mGarageModeService = new GarageModeService(mContext);mAppFocusService = new AppFocusService(serviceContext, mSystemActivityMonitoringService);mCarAudioService = new CarAudioService(serviceContext);mCarNightService = new CarNightService(serviceContext, mCarPropertyService);mFixedActivityService = new FixedActivityService(serviceContext);mInstrumentClusterService = new InstrumentClusterService(serviceContext,mAppFocusService, mCarInputService);mSystemStateControllerService = new SystemStateControllerService(serviceContext, mCarAudioService, this);mCarStatsService = new CarStatsService(serviceContext);mCarStatsService.init();if (mFeatureController.isFeatureEnabled(Car.VEHICLE_MAP_SERVICE)) {mVmsBrokerService = new VmsBrokerService(mContext, mCarStatsService);} else {mVmsBrokerService = null;}if (mFeatureController.isFeatureEnabled(Car.DIAGNOSTIC_SERVICE)) {mCarDiagnosticService = new CarDiagnosticService(serviceContext,mHal.getDiagnosticHal());} else {mCarDiagnosticService = null;}if (mFeatureController.isFeatureEnabled(Car.STORAGE_MONITORING_SERVICE)) {mCarStorageMonitoringService = new CarStorageMonitoringService(serviceContext,systemInterface);} else {mCarStorageMonitoringService = null;}mCarConfigurationService =new CarConfigurationService(serviceContext, new JsonReaderImpl());mCarLocationService = new CarLocationService(serviceContext);mCarTrustedDeviceService = new CarTrustedDeviceService(serviceContext);mCarMediaService = new CarMediaService(serviceContext, mCarUserService);mCarBugreportManagerService = new CarBugreportManagerService(serviceContext);if (!Build.IS_USER) {mCarExperimentalFeatureServiceController = new CarExperimentalFeatureServiceController(serviceContext);} else {mCarExperimentalFeatureServiceController = null;}if (carWatchdogService == null) {mCarWatchdogService = new CarWatchdogService(serviceContext);} else {mCarWatchdogService = carWatchdogService;}//  将电源服务，添加到Car本地服务List中-----------------------------CarLocalServices.addService(CarPowerManagementService.class, mCarPowerManagementService);CarLocalServices.addService(CarPropertyService.class, mCarPropertyService);CarLocalServices.addService(CarUserService.class, mCarUserService);CarLocalServices.addService(CarTrustedDeviceService.class, mCarTrustedDeviceService);CarLocalServices.addService(CarUserNoticeService.class, mCarUserNoticeService);CarLocalServices.addService(SystemInterface.class, mSystemInterface);CarLocalServices.addService(CarDrivingStateService.class, mCarDrivingStateService);CarLocalServices.addService(PerUserCarServiceHelper.class, mPerUserCarServiceHelper);CarLocalServices.addService(FixedActivityService.class, mFixedActivityService);CarLocalServices.addService(VmsBrokerService.class, mVmsBrokerService);CarLocalServices.addService(CarOccupantZoneService.class, mCarOccupantZoneService);CarLocalServices.addService(AppFocusService.class, mAppFocusService);// Be careful with order. Service depending on other service should be inited later.List<CarServiceBase> allServices = new ArrayList<>();allServices.add(mFeatureController);allServices.add(mCarUserService);allServices.add(mSystemActivityMonitoringService);//  将电源服务，添加到Car服务List中-----------------------------allServices.add(mCarPowerManagementService);allServices.add(mCarPropertyService);allServices.add(mCarDrivingStateService);allServices.add(mCarOccupantZoneService);allServices.add(mCarUXRestrictionsService);addServiceIfNonNull(allServices, mOccupantAwarenessService);allServices.add(mCarPackageManagerService);allServices.add(mCarInputService);allServices.add(mGarageModeService);addServiceIfNonNull(allServices, mCarUserNoticeService);allServices.add(mAppFocusService);allServices.add(mCarAudioService);allServices.add(mCarNightService);allServices.add(mFixedActivityService);allServices.add(mInstrumentClusterService);allServices.add(mSystemStateControllerService);allServices.add(mPerUserCarServiceHelper);allServices.add(mCarBluetoothService);allServices.add(mCarProjectionService);addServiceIfNonNull(allServices, mCarDiagnosticService);addServiceIfNonNull(allServices, mCarStorageMonitoringService);allServices.add(mCarConfigurationService);addServiceIfNonNull(allServices, mVmsBrokerService);allServices.add(mCarTrustedDeviceService);allServices.add(mCarMediaService);allServices.add(mCarLocationService);allServices.add(mCarBugreportManagerService);allServices.add(mCarWatchdogService);// Always put mCarExperimentalFeatureServiceController in last.addServiceIfNonNull(allServices, mCarExperimentalFeatureServiceController);mAllServices = allServices.toArray(new CarServiceBase[allServices.size()]);}
}

• CarPower服务启动后，会注册成为PowerHalService的监听者。并主动发出WAIT_FOR_VHALL（初始状态）告知CarPower的监听者，并取一下当前的屏幕亮度发送给VHAL。并连接Native层的CarPowerPolicyService来初始化电源管理政策。

// packages/services/Car/service/src/com/android/car/CarPowerManagementService.java/*** Power Management service class for cars. Controls the power states and interacts with other* parts of the system to ensure its own state.*/
public class CarPowerManagementService extends ICarPower.Stub implementsCarServiceBase, PowerHalService.PowerEventListener {public CarPowerManagementService(Context context, PowerHalService powerHal,SystemInterface systemInterface, CarUserService carUserService) {this(context, context.getResources(), powerHal, systemInterface, UserManager.get(context),carUserService, new InitialUserSetter(context,(u) -> carUserService.setInitialUser(u),context.getString(R.string.default_guest_name)),IVoiceInteractionManagerService.Stub.asInterface(ServiceManager.getService(Context.VOICE_INTERACTION_MANAGER_SERVICE)));}@VisibleForTestingpublic CarPowerManagementService(Context context, Resources resources, PowerHalService powerHal,SystemInterface systemInterface, UserManager userManager, CarUserService carUserService,InitialUserSetter initialUserSetter,IVoiceInteractionManagerService voiceInteractionService) {mContext = context;mHal = powerHal;mSystemInterface = systemInterface;mUserManager = userManager;mDisableUserSwitchDuringResume = resources.getBoolean(R.bool.config_disableUserSwitchDuringResume);mShutdownPrepareTimeMs = resources.getInteger(R.integer.maxGarageModeRunningDurationInSecs) * 1000;mSwitchGuestUserBeforeSleep = resources.getBoolean(R.bool.config_switchGuestUserBeforeGoingSleep);if (mShutdownPrepareTimeMs < MIN_MAX_GARAGE_MODE_DURATION_MS) {Slog.w(TAG,"maxGarageModeRunningDurationInSecs smaller than minimum required, resource:"+ mShutdownPrepareTimeMs + "(ms) while should exceed:"+  MIN_MAX_GARAGE_MODE_DURATION_MS + "(ms), Ignore resource.");mShutdownPrepareTimeMs = MIN_MAX_GARAGE_MODE_DURATION_MS;}mUserService = carUserService;mInitialUserSetter = initialUserSetter;mVoiceInteractionManagerService = voiceInteractionService;mWifiManager = context.getSystemService(WifiManager.class);mWifiStateFile = new AtomicFile(new File(mSystemInterface.getSystemCarDir(), WIFI_STATE_FILENAME));}
}@Override
public void init() {mPolicyReader.init();mPowerComponentHandler.init();mHal.setListener(this);if (mHal.isPowerStateSupported()) {// 发出初始化状态-------------------------------------------// Initialize CPMS in WAIT_FOR_VHAL stateonApPowerStateChange(CpmsState.WAIT_FOR_VHAL, CarPowerStateListener.WAIT_FOR_VHAL);} else {Slogf.w(TAG, "Vehicle hal does not support power state yet.");onApPowerStateChange(CpmsState.ON, CarPowerStateListener.ON);}//  监控屏幕状态，这个函数中会将屏幕亮度发给Vehicle HALmSystemInterface.startDisplayStateMonitoring(this);//  连接Car PowerPolicy服务，初始化电源政策connectToPowerPolicyDaemon();
}

• CarPower启动会立刻向监听者和VehicleHAL发出WAIT_FOR_VHAL这个状态

// packages/services/Car/service/src/com/android/car/power/CarPowerManagementService.java
private void doHandlePowerStateChange() {CpmsState state;synchronized (mLock) {state = mPendingPowerStates.peekFirst();mPendingPowerStates.clear();if (state == null) {Slogf.e(TAG, "Null power state was requested");return;}Slogf.i(TAG, "doHandlePowerStateChange: newState=%s", state.name());if (!needPowerStateChangeLocked(state)) {return;}// now real power change happens. Whatever was queued before should be all cancelled.releaseTimerLocked();mCurrentState = state;}mHandler.cancelProcessingComplete();Slogf.i(TAG, "setCurrentState %s", state);CarStatsLogHelper.logPowerState(state.mState);switch (state.mState) {case CpmsState.WAIT_FOR_VHAL://  处理WAIT_FOR_VHAL状态----------------------------handleWaitForVhal(state);break;case CpmsState.ON:handleOn();break;case CpmsState.SHUTDOWN_PREPARE:handleShutdownPrepare(state);break;case CpmsState.SIMULATE_SLEEP:simulateShutdownPrepare();break;case CpmsState.WAIT_FOR_FINISH:handleWaitForFinish(state);break;case CpmsState.SUSPEND:// Received FINISH from VHALhandleFinish();break;default:// Illegal state// TODO:  Throw exception?break;}
}private void handleWaitForVhal(CpmsState state) {int carPowerStateListenerState = state.mCarPowerStateListenerState;// TODO(b/177478420): Restore Wifi, Audio, Location, and Bluetooth, if they are artificially// modified for S2R.mSilentModeHandler.querySilentModeHwState();// 给CarPower服务的监听者发送状态sendPowerManagerEvent(carPowerStateListenerState);// Inspect CarPowerStateListenerState to decide which message to send via VHALswitch (carPowerStateListenerState) {case CarPowerStateListener.WAIT_FOR_VHAL:// 通过PowerHAlService向VehicleHAL发送状态mHal.sendWaitForVhal();break;case CarPowerStateListener.SHUTDOWN_CANCELLED:mShutdownOnNextSuspend = false; // This cancels the "NextSuspend"mHal.sendShutdownCancel();break;case CarPowerStateListener.SUSPEND_EXIT:mHal.sendSleepExit();break;}if (mWifiAdjustmentForSuspend) restoreWifi();
}

• 接下来，MCU会给VehicleHAL发送电源通知，VehicleHAL通知(AP_POWER_STATE_REQ= ON) 给CarPower服务。

@Override
public void onHalEvents(List<VehiclePropValue> values) {PowerEventListener listener;synchronized (mLock) {if (mListener == null) {if (mQueuedEvents == null) {mQueuedEvents = new LinkedList<>();}mQueuedEvents.addAll(values);return;}listener = mListener;}dispatchEvents(values, listener);
}private void dispatchEvents(List<VehiclePropValue> values, PowerEventListener listener) {for (VehiclePropValue v : values) {switch (v.prop) {case AP_POWER_STATE_REPORT:// Ignore this property event. It was generated inside of CarService.break;case AP_POWER_STATE_REQ:// 发送的是这个状态------ AP_POWER_STATE_REQ=ONint state = v.value.int32Values.get(VehicleApPowerStateReqIndex.STATE);int param = v.value.int32Values.get(VehicleApPowerStateReqIndex.ADDITIONAL);Slog.i(CarLog.TAG_POWER, "Received AP_POWER_STATE_REQ="+ powerStateReqName(state) + " param=" + param);listener.onApPowerStateChange(new PowerState(state, param));break;case DISPLAY_BRIGHTNESS:{int maxBrightness;synchronized (mLock) {maxBrightness = mMaxDisplayBrightness;}int brightness = v.value.int32Values.get(0) * MAX_BRIGHTNESS / maxBrightness;if (brightness < 0) {Slog.e(CarLog.TAG_POWER, "invalid brightness: " + brightness+ ", set to 0");brightness = 0;} else if (brightness > MAX_BRIGHTNESS) {Slog.e(CarLog.TAG_POWER, "invalid brightness: " + brightness + ", set to "+ MAX_BRIGHTNESS);brightness = MAX_BRIGHTNESS;}Slog.i(CarLog.TAG_POWER, "Received DISPLAY_BRIGHTNESS=" + brightness);listener.onDisplayBrightnessChange(brightness);}break;}}
}

• CarPowerService接收到 AP_POWER_STATE_REQ= ON，认为当前是电源ON的状态。应用电源策略（告知机能模块可以使能）、通知观察者电源状态为ON，然后向VehicleHAL进行回复（也叫report）

packages/services/Car/service/src/com/android/car/power/CarPowerManagementService.java@Override
public void onApPowerStateChange(PowerState state) {synchronized (mLock) {mPendingPowerStates.addFirst(new CpmsState(state));mLock.notify();}// 发给handler，在单独的线程中处理。最终调用的是自身的doHandlePowerStateChange函数mHandler.handlePowerStateChange();
}private void doHandlePowerStateChange() {CpmsState state;synchronized (mLock) {state = mPendingPowerStates.peekFirst();mPendingPowerStates.clear();if (state == null) {Slogf.e(TAG, "Null power state was requested");return;}Slogf.i(TAG, "doHandlePowerStateChange: newState=%s", state.name());if (!needPowerStateChangeLocked(state)) {return;}// now real power change happens. Whatever was queued before should be all cancelled.releaseTimerLocked();mCurrentState = state;}mHandler.cancelProcessingComplete();Slogf.i(TAG, "setCurrentState %s", state);CarStatsLogHelper.logPowerState(state.mState);switch (state.mState) {case CpmsState.WAIT_FOR_VHAL:handleWaitForVhal(state);break;case CpmsState.ON:// 处理电源ON----------------------------------------------------------------handleOn();break;case CpmsState.SHUTDOWN_PREPARE:handleShutdownPrepare(state);break;case CpmsState.SIMULATE_SLEEP:simulateShutdownPrepare();break;case CpmsState.WAIT_FOR_FINISH:handleWaitForFinish(state);break;case CpmsState.SUSPEND:// Received FINISH from VHALhandleFinish();break;default:// Illegal state// TODO:  Throw exception?break;}
}@VisibleForTesting
void handleOn() {if (factoryResetIfNeeded()) return;// If current user is a Guest User, we want to inform CarUserNoticeService not to show// notice for current user, and show user notice only for the target user.if (!mSwitchGuestUserBeforeSleep) {updateCarUserNoticeServiceIfNecessary();}boolean isPreemptive;synchronized (mLock) {isPreemptive = mPolicyReader.isPreemptivePowerPolicy(mCurrentPowerPolicyId);}if (!mSilentModeHandler.isSilentMode() && isPreemptive) {cancelPreemptivePowerPolicy();} else {// 应用电源策略---------------------------------applyDefaultPowerPolicyForState(VehicleApPowerStateReport.ON,PolicyReader.POWER_POLICY_ID_ALL_ON);}// 通知观察者电源状态为ON------------------------sendPowerManagerEvent(CarPowerStateListener.ON);// 通过PowerHAlServicee，回复Vehicle HAL（VehicleApPowerStateReport.ON）mHal.sendOn();synchronized (mLock) {if (mIsBooting) {Slogf.d(TAG, "handleOn(): called on boot");mIsBooting = false;return;}}try {mUserService.onResume();} catch (Exception e) {Slogf.e(TAG, e, "Could not switch user on resume");}
}

• 到这里，CarPower主要的开机处理流程完毕。实际上可以看出来，主要是接收Vehicle HAl Event（包括回复VehicleHAL状态），告知监听者电源状态、应用电源政策使能相关机能。并且在启动阶段，取了一下当前的屏幕亮度，告知VehicleHAL（最终是告知MCU）。当然还有一些其他的处理，比如用户服务的恢复，有兴趣的可以读一下这部分代码。
• CarPowerService上电时序图。