Android Framework系列—CarPower深度睡眠

之前博客说了CarPower的开机启动流程
这里分析一下，Android CarPower实现深度睡眠的流程。
首先，什么是深度睡眠(Deep Sleep)?

Android进入Deep Sleep后，关闭屏幕、关闭CPU的电源，保持RAM的电源（激活状态）。深度睡眠会进行Suspend-to-RAM挂起到内存（做车载的经常会听到的STR）。当然深度睡眠，还一种是挂起到硬盘（Suspend-to-Disk），不过目前主要用的是STR。所以STR是深度睡眠时的状态，但STR不等于深度睡眠。

DeepSleep或STR，需要内核配合实现。通过这种技术，车载系统可以进入低能耗模式，同时又可以再用户需要时实现快速(非常快，因为从内存中恢复状态）的启动。
感觉这种方式，跟snapshot快启动有点类似。不过是两个概念上的事情了。

下面摘自Android官网对这种状态的介绍。

也称为“挂起到 RAM”（S2R 或 STR）。将 SoC 置于 S3 电源模式，CPU 断电而 RAM 仍通电。

VMCU 应将 SoC 置于“深度睡眠”状态，并断开应用处理器的电源。然后，AAOS 将进入“挂起到 RAM”状态，但不执行任何代码。

整套深度睡眠的实现，涉及的主要模块（这里指单Android系统。当前还有Qnx之类的hypervisor）

• MCU/VMCU：控制电源，发送电源状态给SOC（Android）
• Vehicle HAL：一般由硬件供应商实现，与MCU通信（can、以太方式）
• CarPowerManagerService(CPMS): 实现Android侧的电源控制，应用电源策略。
• CarPowerManager(CPM): CPMS的客户端，通知电源状态给应用，等待应用回复状态等。

下面是摘自Android官网的深入睡眠流程描述；

只有 VMCU 可以启动深度睡眠。启动深度睡眠后，VMCU 会通过 VHAL 向 CPMS 发送通知。CPMS 通过使用由 CPM 提供的新状态 ID 调用 onStateChanged() 方法，将状态更改为“关闭准备”并向所有观察者（监控 CPMS 的应用和服务）广播此状态转换。

CPM 在应用/服务与 CPMS 之间进行协调。在 CPM 的 onStateChanged() 方法中，同步调用应用/服务的
onStateChanged() 方法。大多数应用和服务需要完成其准备后才能从该调用返回。特权服务可以在为
PRE_SHUTDOWN_PREPARE、SUSPEND_ENTER 和 POST_SUSPEND_ENTER
返回后，异步继续关闭准备。在此情况下，特权服务应在完成准备时对提供的 CompletablePowerStateChangeFuture
对象调用 complete()。请注意，SHUTDOWN_PREPARE 不允许异步准备。在向 VHAL 发送
DEEP_SLEEP_ENTRY 之前，CPMS 会定期向 VHAL 发送推迟关闭的请求。

当所有 CPM 对象完成关闭准备后，CPMS 会向 VHAL 发送 AP_POWER_STATE_REPORT，VHAL 随后通知
VMCU，告知它 AP 已准备好挂起。CPMS 还会调用其挂起方法以挂起内核。

下面的图，是Android官网对于深度睡眠的时序图。这里贴在这里。后面会根据源码，分析并画一个跟代码对应的时序图。

CPMS深度睡眠代码实现

• 到这里，我们开始分析CPMS的实现。代码基于Android11

首先，VMCU请求挂起。Vehicle HAL （Hal层的nativeservice）发送“AP_POWER_STATE_REQ(SHUTDOWN_PREPARE)”， 这样CarService中的 VehicleHal（Client端 ）就收到了这个通知。一路通知给CPMS进行状态处理。

• packages/services/Car/service/src/com/android/car/hal/VehicleHal.java

public void onPropertyEvent(ArrayList<VehiclePropValue> propValues) {// 省略for (HalServiceBase s : mServicesToDispatch) {//  通知给监听者s.onHalEvents(s.getDispatchList());s.getDispatchList().clear();}mServicesToDispatch.clear();
}

• packages/services/Car/service/src/com/android/car/hal/PowerHalService.java

@Override
public void onHalEvents(List<VehiclePropValue> values) {// 省略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:int state = v.value.int32Values.get(VehicleApPowerStateReqIndex.STATE);int param = v.value.int32Values.get(VehicleApPowerStateReqIndex.ADDITIONAL);Log.i(CarLog.TAG_POWER, "Received AP_POWER_STATE_REQ="+ powerStateReqName(state) + " param=" + param);// 通知状态给CPMS对象// AP_POWER_STATE_REQ(SHUTDOWN_PREPARE, CAN_SLEEP)listener.onApPowerStateChange(new PowerState(state, param));break;case DISPLAY_BRIGHTNESS:{// 省略}break;}}
}

• packages/services/Car/service/src/com/android/car/CarPowerManagementService.java

@Override
public void onApPowerStateChange(PowerState state) {synchronized (mLock) {mPendingPowerStates.addFirst(new CpmsState(state));mLock.notify();}mHandler.handlePowerStateChange();
}private void handlePowerStateChange() {Message msg = obtainMessage(MSG_POWER_STATE_CHANGE);sendMessage(msg);
}@Override
public void handleMessage(Message msg) {CarPowerManagementService service = mService.get();if (service == null) {Slog.i(TAG, "handleMessage null service");return;}switch (msg.what) {case MSG_POWER_STATE_CHANGE:// 开始处理//  service是doHandlePowerStateChange对象service.doHandlePowerStateChange();break;// 省略}
}private void doHandlePowerStateChange() {// 省略了mCurrentState = state;switch (state.mState) {case CpmsState.WAIT_FOR_VHAL:handleWaitForVhal(state);break;case CpmsState.ON:handleOn();break;case CpmsState.SHUTDOWN_PREPARE:// 处理SHUTDOWN_PREPAREhandleShutdownPrepare(state);break;// 省略default:// Illegal state// TODO:  Throw exception?break;}
}

CarPowerManagementService开始处理SHUTDOWN_PREPARE。主要是关闭VR交互、关闭屏幕。通知状态给CPMS的客户端，启动超时等待客户端处理完成（使用****CarPowerStateListenerWithCompletion的客户端）

• packages/services/Car/service/src/com/android/car/CarPowerManagementService.java

private void handleShutdownPrepare(CpmsState newState) {setVoiceInteractionDisabled(true);mSystemInterface.setDisplayState(false);// Shutdown on finish if the system doesn't support deep sleep or doesn't allow it.// 通知状态给客户端sendPowerManagerEvent(CarPowerStateListener.SHUTDOWN_PREPARE);mHal.sendShutdownPrepare();doHandlePreprocessing();
}private void doHandlePreprocessing() {int intervalMs;int pollingCount;synchronized (mLock) {intervalMs = mShutdownPollingIntervalMs;pollingCount = (mShutdownPrepareTimeMs / mShutdownPollingIntervalMs) + 1;}if (Build.IS_USERDEBUG || Build.IS_ENG) {// 这里省略了，主要是可以通过属性，修改超时时间。}Slog.i(TAG, "processing before shutdown expected for: "+ mShutdownPrepareTimeMs + " ms, adding polling:" + pollingCount);// 启动超时任务，定期检查。那些使用 CarPowerStateListenerWithCompletion//（带有future，告知CPMS自己是否处理完了）的应用端是否处理完毕。// 如果超时还没完成，强制走DeepSleep流程。synchronized (mLock) {mProcessingStartTime = SystemClock.elapsedRealtime();releaseTimerLocked();mTimer = new Timer();mTimerActive = true;mTimer.scheduleAtFixedRate(new ShutdownProcessingTimerTask(pollingCount),0 /*delay*/,intervalMs);}if (mSwitchGuestUserBeforeSleep) {switchToNewGuestIfNecessary();}
}// 超时处理Task
private class ShutdownProcessingTimerTask extends TimerTask {private final int mExpirationCount;private int mCurrentCount;private ShutdownProcessingTimerTask(int expirationCount) {mExpirationCount = expirationCount;mCurrentCount = 0;}@Overridepublic void run() {synchronized (mLock) {if (!mTimerActive) {// Ignore timer expiration since we got cancelledreturn;}mCurrentCount++;if (mCurrentCount > mExpirationCount) {// 超时处理。给Vehicle HAL通知DEEP_SLEEP_ENTRY，告知可以开始进入深入睡眠状态。PowerHandler handler;releaseTimerLocked();handler = mHandler;handler.handleProcessingComplete();} else {// 定期通过PowerServiceHAL向Vehicle HAL发送延时通知。mHal.sendShutdownPostpone(SHUTDOWN_EXTEND_MAX_MS);}}}
}

这里假设走正常的处理了，即所有客户端（CarPowerStateListenerWithCompletion）期限内完成了处理。那么CPMS，就会通过PowerserviceHAL告知 VehicleHAL “DEEP_SLEEP_ENTRY”状态。下面是CarPowerStateListenerWithCompletion的一个例子。

mCarPowerManager.setListenerWithCompletion(mCarPowerStateListener);
private final CarPowerStateListenerWithCompletion mCarPowerStateListener =new CarPowerStateListenerWithCompletion() {@Overridepublic void onStateChanged(int state, CompletableFuture<Void> future) {if (state == CarPowerManager.CarPowerStateListener.SHUTDOWN_PREPARE) {// 例子，应用端处理完成后，调用future.complete 告知CPMS处理完成if (future != null) {future.complete(null);}}}
};

• packages/services/Car/service/src/com/android/car/CarPowerManagementService.java

// future.complete 会触发CPMS这个函数。
@Override
public void finished(ICarPowerStateListener listener) {ICarImpl.assertPermission(mContext, Car.PERMISSION_CAR_POWER);ICarImpl.assertCallingFromSystemProcessOrSelf();finishedImpl(listener.asBinder());
}private void finishedImpl(IBinder binder) {boolean allAreComplete;synchronized (mLock) {mListenersWeAreWaitingFor.remove(binder);allAreComplete = mListenersWeAreWaitingFor.isEmpty();}// 所有Listener处理完成了。if (allAreComplete) {signalComplete();}
}private void signalComplete() {if (mCurrentState.mState == CpmsState.SHUTDOWN_PREPARE|| mCurrentState.mState == CpmsState.SIMULATE_SLEEP) {PowerHandler powerHandler;// All apps are ready to shutdown/suspend.synchronized (mLock) {if (!mShutdownOnFinish) {if (mLastSleepEntryTime > mProcessingStartTime&& mLastSleepEntryTime < SystemClock.elapsedRealtime()) {Slog.i(TAG, "signalComplete: Already slept!");return;}}powerHandler = mHandler;}Slog.i(TAG, "Apps are finished, call handleProcessingComplete()");powerHandler.handleProcessingComplete();}
}private void handleProcessingComplete() {removeMessages(MSG_PROCESSING_COMPLETE);Message msg = obtainMessage(MSG_PROCESSING_COMPLETE);sendMessage(msg);
}@Override
public void handleMessage(Message msg) {CarPowerManagementService service = mService.get();if (service == null) {Slog.i(TAG, "handleMessage null service");return;}switch (msg.what) {case MSG_POWER_STATE_CHANGE:service.doHandlePowerStateChange();break;case MSG_DISPLAY_BRIGHTNESS_CHANGE:service.doHandleDisplayBrightnessChange(msg.arg1);break;case MSG_MAIN_DISPLAY_STATE_CHANGE:service.doHandleMainDisplayStateChange((Boolean) msg.obj);break;case MSG_PROCESSING_COMPLETE:// 走这里service.doHandleProcessingComplete();break;}
}private void doHandleProcessingComplete() {int listenerState;synchronized (mLock) {releaseTimerLocked();if (!mShutdownOnFinish && mLastSleepEntryTime > mProcessingStartTime) {// entered sleep after processing start. So this could be duplicate request.Slog.w(TAG, "Duplicate sleep entry request, ignore");return;}// 可以设置关机，即不进入挂起。// 默认状态，走SUSPEND_ENTERlistenerState = mShutdownOnFinish? CarPowerStateListener.SHUTDOWN_ENTER : CarPowerStateListener.SUSPEND_ENTER;}// 处理状态变化（这个函数是两参的，并且是private的）onApPowerStateChange(CpmsState.WAIT_FOR_FINISH, listenerState);
}private void onApPowerStateChange(int apState, int carPowerStateListenerState) {CpmsState newState = new CpmsState(apState, carPowerStateListenerState);synchronized (mLock) {mPendingPowerStates.addFirst(newState);mLock.notify();}// 用 handler线程处理。下面省略了中间流程，最终调用的是doHandlePowerStateChangemHandler.handlePowerStateChange();
}private void doHandlePowerStateChange() {mCurrentState = state;switch (state.mState) {// 省略case CpmsState.WAIT_FOR_FINISH:// 走这里handleWaitForFinish(state);break;// 省略default:// Illegal state// TODO:  Throw exception?break;}
}private void handleWaitForFinish(CpmsState state) {//  通知给CPMS的监听者当前状态sendPowerManagerEvent(state.mCarPowerStateListenerState);int wakeupSec;synchronized (mLock) {// If we're shutting down immediately, don't schedule// a wakeup time.//  可以设置，进入休眠状态后的唤醒时间（默认是不设置的），0表示一直Sleep（除非VMCU主动唤起）wakeupSec = mGarageModeShouldExitImmediately ? 0 : mNextWakeupSec;}switch (state.mCarPowerStateListenerState) {case CarPowerStateListener.SUSPEND_ENTER:// 	// 给Vehicle  HAL发送状态// 发送的是DEEP_SLEEP_ENTRY，告知可以进入休眠状态了。mHal.sendSleepEntry(wakeupSec);break;case CarPowerStateListener.SHUTDOWN_ENTER:mHal.sendShutdownStart(wakeupSec);break;}
}

到这里，就是告诉了VMCU，Android 挂起Ready了，也就是一切准备完成。然后MCU就会发送AP_POWER_STATE_REQ(FINISHED)，告知Android侧调用Linux内核的实现，把自己挂起来（Supend）。消息通知流程，跟上面的onPropertyEvent一致，这部分下面就省略了。

• packages/services/Car/service/src/com/android/car/CarPowerManagementService.java

private void doHandlePowerStateChange() {mCurrentState = state;switch (state.mState) {// 省略case CpmsState.SUSPEND:// Received FINISH from VHAL// 走这里handleFinish();break;default:// Illegal state// TODO:  Throw exception?break;}
}private void handleFinish() {// 省略// 关闭VoicesetVoiceInteractionDisabled(true);// To make Kernel implementation simpler when going into sleep.disableWifi();if (mustShutDown) {// shutdown HUmSystemInterface.shutdown();} else {// 处理深入睡眠doHandleDeepSleep(simulatedMode);}mShutdownOnNextSuspend = false;
}private void doHandleDeepSleep(boolean simulatedMode) {// keep holding partial wakelock to prevent entering sleep before enterDeepSleep call// enterDeepSleep should force sleep entry even if wake lock is kept.mSystemInterface.switchToPartialWakeLock();mHandler.cancelProcessingComplete();synchronized (mLock) {mLastSleepEntryTime = SystemClock.elapsedRealtime();}int nextListenerState;if (simulatedMode) {// 省略} else {// 最终会调用Kernel接口，Supend To RAM（感兴趣的小伙伴可以顺着这个接口看下去。// 挂成功的情况下面，下面的代码就不会走了（CPU都没电了）。// 之后的代码，就是CPU上电后的恢复流程了。// 可以看出恢复前，要刷新一下屏幕亮度。然后走WAIT_FOR_VHAL状态。boolean sleepSucceeded = suspendWithRetries();if (!sleepSucceeded) {// Suspend failed and we shut down instead.// We either won't get here at all or we will power off very soon.return;}// We suspended and have now resumednextListenerState = CarPowerStateListener.SUSPEND_EXIT;}synchronized (mLock) {mIsResuming = true;// Any wakeup time from before is no longer valid.mNextWakeupSec = 0;}Slog.i(TAG, "Resuming after suspending");mSystemInterface.refreshDisplayBrightness();onApPowerStateChange(CpmsState.WAIT_FOR_VHAL, nextListenerState);
}

综上是Android CarPower的深入睡眠睡眠主要流程，实际开发过程中。根据业务进行扩展，一般会添加一个跟CPMS平行，或者基于它的新的电源模块。下面是上面代码的时序图，供参考。