android电源

http://yueguc.javaeye.com/blog/948569

相关文件： 
（1）. SystemServer.java          (frameworks/frameworks/base/services/java/com/android/server) 
（2）. BatteryService.java       (frameworks/frameworks/base/services/java/com/android/server) 
（3）. UEventObserver.java       (frameworks/frameworks/base/core/java/android/os) 
（4）. com_android_server_BatteryService.cpp (frameworks/frameworks/base/services/jni)

电池的信息，电压，温度，充电状态等等，都是由BatteryService来提供的。BatteryService是跑在system_process当中，在系统初始化的时候启动，如下 

     在BatteryService.java中： 
          Log.i(TAG, "Starting Battery Service."); 
          BatteryService battery = new BatteryService(context); 
          ServiceManager.addService("battery", battery); 
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1. 数据来源 
        BatteryService通过JNI（com_android_server_BatteryService.cpp）读取数据。BatteryService通过JNI注册的不仅有函数，还有变量。 如下： 

    //##############在BatteryService.java中声明的变量################ 
    private boolean mAcOnline; 
    private boolean mUsbOnline; 
    private int mBatteryStatus; 
    private int mBatteryHealth; 
    private boolean mBatteryPresent; 
    private int mBatteryLevel; 
    private int mBatteryVoltage; 
    private int mBatteryTemperature; 
    private String mBatteryTechnology; 

    //在BatteryService.java中声明的变量，在com_android_server_BatteryService.cpp中共用，即 在com_android_server_BatteryService.cpp中其实操作的也是BatteryService.java中声明的变量 
   

   gFieldIds.mAcOnline = env->GetFieldID(clazz, "mAcOnline", "Z"); 
    gFieldIds.mUsbOnline = env->GetFieldID(clazz, "mUsbOnline", "Z"); 
    gFieldIds.mBatteryStatus = env->GetFieldID(clazz, "mBatteryStatus", "I"); 
    gFieldIds.mBatteryHealth = env->GetFieldID(clazz, "mBatteryHealth", "I"); 
    gFieldIds.mBatteryPresent = env->GetFieldID(clazz, "mBatteryPresent", "Z"); 
    gFieldIds.mBatteryLevel = env->GetFieldID(clazz, "mBatteryLevel", "I"); 
    gFieldIds.mBatteryTechnology = env->GetFieldID(clazz, "mBatteryTechnology", "Ljava/lang/String;"); 
    gFieldIds.mBatteryVoltage = env->GetFieldID(clazz, "mBatteryVoltage", "I"); 
    gFieldIds.mBatteryTemperature = env->GetFieldID(clazz, "mBatteryTemperature", "I"); 


   
    //上面这些变量的值，对应是从下面的文件中读取的，一只文件存储一个数值。 


    #define AC_ONLINE_PATH "/sys/class/power_supply/ac/online" 
    #define USB_ONLINE_PATH "/sys/class/power_supply/usb/online" 
    #define BATTERY_STATUS_PATH "/sys/class/power_supply/battery/status" 
    #define BATTERY_HEALTH_PATH "/sys/class/power_supply/battery/health" 
    #define BATTERY_PRESENT_PATH "/sys/class/power_supply/battery/present" 
    #define BATTERY_CAPACITY_PATH "/sys/class/power_supply/battery/capacity" 
    #define BATTERY_VOLTAGE_PATH "/sys/class/power_supply/battery/batt_vol" 
    #define BATTERY_TEMPERATURE_PATH "/sys/class/power_supply/battery/batt_temp" 
    #define BATTERY_TECHNOLOGY_PATH "/sys/class/power_supply/battery/technology" 

    Android是运行在Linux内核上面的，/sys/class/power_supply亦是Linux内核下面的目录。至于这些文件时怎么生成的，则是由Platform来控制的。 

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2. 数据传送 
        电池的这些信息是通过何种方式，被其他应用所获得的。可以想到的有两种方式，第一种，应用主动从BatteryService获得数据；第二种，BatteryService主动把数据传送给所关心的应用程序。 

       BatteryService采用的是第二种方式，所有的电池的信息数据是通过Intent传送出去的。在BatteryService.java中，Code如下： 

       Intent intent = new Intent(Intent.ACTION_BATTERY_CHANGED); 
       intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY); 

        intent.putExtra("status", mBatteryStatus); 
        intent.putExtra("health", mBatteryHealth); 
        intent.putExtra("present", mBatteryPresent); 
        intent.putExtra("level", mBatteryLevel); 
        intent.putExtra("scale", BATTERY_SCALE); 
        intent.putExtra("icon-small", icon); 
        intent.putExtra("plugged", mPlugType); 
        intent.putExtra("voltage", mBatteryVoltage); 
        intent.putExtra("temperature", mBatteryTemperature); 
        intent.putExtra("technology", mBatteryTechnology); 

       ActivityManagerNative.broadcastStickyIntent(intent, null); 

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3. 数据接收 
    应用如果想要接收到BatteryService发送出来的电池信息，则需要注册一个Intent为Intent.ACTION_BATTERY_CHANGED的BroadcastReceiver。 

    注册方法如下： 
              IntentFilter mIntentFilter = new IntentFilter(); 
              mIntentFilter.addAction(Intent.ACTION_BATTERY_CHANGED); 
              registerReceiver(mIntentReceiver, mIntentFilter); 

      private BroadcastReceiver mIntentReceiver = new BroadcastReceiver() { 
             @Override 
             public void onReceive(Context context, Intent intent) { 
                   // TODO Auto-generated method stub 
                     String action = intent.getAction(); 
                     if (action.equals(Intent.ACTION_BATTERY_CHANGED)) { 
         
                           int nVoltage = intent.getIntExtra("voltage", 0); 
                           if(nVoltage!=0){        
                                   mVoltage.setText("V: " + nVoltage + "mV - Success..."); 
                          } 
                            else{ 
                                   mVoltage.setText("V: " + nVoltage + "mV - fail..."); 
                            } 
                   }   
              }    
      }; 

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4. 数据更新 
         电池的信息会随着时间不停变化，自然地，就需要考虑如何实时的更新电池的数据信息。在BatteryService启动的时候，会同时通过UEventObserver启动一个onUEvent Thread。 

        每一个Process最多只能有一个onUEvent Thread，即使这个Process中有多个UEventObserver的实例。当在一个Process中，第一次Call startObserving()方法后，这个UEvent thread就启动了。 
而一旦这个UEvent thread启动之后，就不会停止。 
    
     //在BatteryService.java中 
     mUEventObserver.startObserving("SUBSYSTEM=power_supply"); 

     private UEventObserver mUEventObserver = new UEventObserver() { 
        @Override 
        public void onUEvent(UEventObserver.UEvent event) { 
            update(); 
        } 
     }; 

    
     在UEvent thread中会不停调用 update()方法，来更新电池的信息数据。 

    
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5. 附录相关文件： 
（1）. SystemServer.java          (frameworks/frameworks/base/services/java/com/android/server) 
（2）. BatteryService.java       (frameworks/frameworks/base/services/java/com/android/server) 
（3）. UEventObserver.java       (frameworks/frameworks/base/core/java/android/os) 
（4）. com_android_server_BatteryService.cpp (frameworks/frameworks/base/services/jni)

BatteryService作为电池及充电相关的服务，它的实现非常简单： 

o 监听UEvent，读取sysfs里中的状态。 

实现了一个UEvent的观察者。uevent是Linux内核用来向用户空间主动上报事件的机制，对于JAVA程序来说，只实现UEventObserver的虚函数onUEvent，然后注册即可。 

    private UEventObserver mUEventObserver = new UEventObserver() { 
        @Override 
        public void onUEvent(UEventObserver.UEvent event) { 
            update(); 
        } 
    }; 

这里只关注power_supply的事件： 

mUEventObserver.startObserving("SUBSYSTEM=power_supply"); 

当有power_supply相关的事件上报时，就会调用update函数。 

update先调用native_update从sysfs中读取相关状态（com_android_server_BatteryService.cpp）： 

Linux驱动提供了下列文件，供应用程序获取电源相关状态： 

#define AC_ONLINE_PATH "/sys/class/power_supply/ac/online" 
#define USB_ONLINE_PATH "/sys/class/power_supply/usb/online" 
#define BATTERY_STATUS_PATH "/sys/class/power_supply/battery/status" 
#define BATTERY_HEALTH_PATH "/sys/class/power_supply/battery/health" 
#define BATTERY_PRESENT_PATH "/sys/class/power_supply/battery/present" 
#define BATTERY_CAPACITY_PATH "/sys/class/power_supply/battery/capacity" 
#define BATTERY_VOLTAGE_PATH "/sys/class/power_supply/battery/batt_vol" 
#define BATTERY_TEMPERATURE_PATH "/sys/class/power_supply/battery/batt_temp" 
#define BATTERY_TECHNOLOGY_PATH "/sys/class/power_supply/battery/technology" 

在＜DA9034驱动程序阅读笔记(6)＞一文中，我已经提到drivers/power/micco_power.c里注册了充电器(ac)、 usb和电池(battery)三个power_supply。各个power_supply提供的属性和上述文件是对应的，从这些文件中可以读到充电器 (ac)、usb和电池(battery)三个power_supply的相应状态。 

update然后根据读到的状态更新BatteryService的成员变量，并广播一个Intent来通知其它关注电源状态的组件。 

    private final void sendIntent() { 
        //  Pack up the values and broadcast them to everyone 
        Intent intent = new Intent(Intent.ACTION_BATTERY_CHANGED); 
        intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY); 
        try { 
            mBatteryStats.setOnBattery(mPlugType == BATTERY_PLUGGED_NONE, mBatteryLevel); 
        } catch (RemoteException e) { 
            // Should never happen. 
        } 

        int icon = getIcon(mBatteryLevel); 

        intent.putExtra("status", mBatteryStatus); 
        intent.putExtra("health", mBatteryHealth); 
        intent.putExtra("present", mBatteryPresent); 
        intent.putExtra("level", mBatteryLevel); 
        intent.putExtra("scale", BATTERY_SCALE); 
        intent.putExtra("icon-small", icon); 
        intent.putExtra("plugged", mPlugType); 
        intent.putExtra("voltage", mBatteryVoltage); 
        intent.putExtra("temperature", mBatteryTemperature); 
        intent.putExtra("technology", mBatteryTechnology ); 

        ActivityManagerNative.broadcastStickyIntent(intent, null); 
    } 

关注ACTION_BATTERY_CHANGED的地方有好几个： 

o KeyguardUpdateMonitor 这里主要是用来更新锁屏界面下的电池状态。还有低电警告和关机也是在这里做的。 

    private void handleBatteryUpdate(int pluggedInStatus, int batteryLevel) { 
        if (DEBUG) Log.d(TAG, "handleBatteryUpdate"); 
        final boolean pluggedIn = isPluggedIn(pluggedInStatus); 

        if (isBatteryUpdateInteresting(pluggedIn, batteryLevel)) { 
            mBatteryLevel = batteryLevel; 
            mDevicePluggedIn = pluggedIn; 
            for (int i = 0; i < mInfoCallbacks.size(); i++) { 
                mInfoCallbacks.get(i).onRefreshBatteryInfo( 
                        shouldShowBatteryInfo(), pluggedIn, batteryLevel); 
            } 
        } 

        // shut down gracefully if our battery is critically low and we are not powered 
        if (batteryLevel == 0 && 
                pluggedInStatus != BATTERY_STATUS_CHARGING && 
                pluggedInStatus != BATTERY_STATUS_UNKNOWN) { 

            ShutdownThread.shutdownAfterDisablingRadio(mContext, false); 

        } 
    } 

o NotificationManagerService 用来更新充电状态（LED) 

            if (action.equals(Intent.ACTION_BATTERY_CHANGED)) { 
                boolean batteryCharging = (intent.getIntExtra("plugged", 0) != 0); 
                int level = intent.getIntExtra("level", -1); 
                boolean batteryLow = (level >= 0 && level <= Power.LOW_BATTERY_THRESHOLD); 
                int status = intent.getIntExtra("status", BatteryManager.BATTERY_STATUS_UNKNOWN); 
                boolean batteryFull = (status == BatteryManager.BATTERY_STATUS_FULL || level >= 90); 

                if (batteryCharging != mBatteryCharging || 
                        batteryLow != mBatteryLow || 
                        batteryFull != mBatteryFull) { 
                    mBatteryCharging = batteryCharging; 
                    mBatteryLow = batteryLow; 
                    mBatteryFull = batteryFull; 
                    updateLights(); 
                } 
            } 

o PowerManagerService 这里主要是做两件事件，先是检查是否在充电时不允许睡眠，并采用相应的行动，其次是触发一个用户行为（会影响下一次睡眠的时间）。 

    private final class BatteryReceiver extends BroadcastReceiver { 
        @Override 
        public void onReceive(Context context, Intent intent) { 
            synchronized (mLocks) { 
                boolean wasPowered = mIsPowered; 
                mIsPowered = mBatteryService.isPowered(); 

                if (mIsPowered != wasPowered) { 
                    // update mStayOnWhilePluggedIn wake lock 
                    updateWakeLockLocked(); 

                    // treat plugging and unplugging the devices as a user activity. 
                    // users find it disconcerting when they unplug the device 
                    // and it shuts off right away. 
                    // temporarily set mUserActivityAllowed to true so this will work 
                    // even when the keyguard is on. 
                    synchronized (mLocks) { 
                        boolean savedActivityAllowed = mUserActivityAllowed; 
                        mUserActivityAllowed = true; 
                        userActivity(SystemClock.uptimeMillis(), false); 
                        mUserActivityAllowed = savedActivityAllowed; 
                    } 
                } 
            } 
        } 
    } 

o LocationManagerService 这里似乎没有什么用处，我没找到mCollector赋值的地方。 

             if (action.equals(Intent.ACTION_BATTERY_CHANGED)) { 
                log("PowerStateBroadcastReceiver: Battery changed"); 
                synchronized (mLocationListeners) { 
                    int scale = intent.getIntExtra(BATTERY_EXTRA_SCALE, 100); 
                    int level = intent.getIntExtra(BATTERY_EXTRA_LEVEL, 0); 
                    boolean plugged = intent.getIntExtra(BATTERY_EXTRA_PLUGGED, 0) != 0; 

                    // Notify collector battery state 
                    if (mCollector != null) { 
                        mCollector.updateBatteryState(scale, level, plugged); 
                    } 
                } 
            } 

o WifiService 根据电源状态来决定是否需要定时唤醒(没搞得太明白，看Wifi服务时再研究)。 

if (action.equals(Intent.ACTION_BATTERY_CHANGED)) { 
                /* 
                 * Set a timer to put Wi-Fi to sleep, but only if the screen is off 
                 * AND we are transitioning from a state in which the device was supposed 
                 * to stay awake to a state in which it is not supposed to stay awake. 
                 * If "stay awake" state is not changing, we do nothing, to avoid resetting 
                 * the already-set timer. 
                 */ 
                int pluggedType = intent.getIntExtra("plugged", 0); 
                if (mScreenOff && shouldWifiStayAwake(stayAwakeConditions, mPluggedType) && 
                        !shouldWifiStayAwake(stayAwakeConditions, pluggedType)) { 
                    long triggerTime = System.currentTimeMillis() + idleMillis; 
                    mAlarmManager.set(AlarmManager.RTC_WAKEUP, triggerTime, mIdleIntent); 
                    mPluggedType = pluggedType; 
                    return; 
                } 
                mPluggedType = pluggedType; 
            } 

o StatusBarPolicy用来更新状态栏上的充电图标。 

if (action.equals(Intent.ACTION_BATTERY_CHANGED)) { 
                updateBattery(intent); 
            }