android电源

于 2011-04-01 18:54:00 发布
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分类专栏： android进阶 文章标签： android path linux内核 thread server 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);
========================================================================================
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。

-----------------------------------------------------------------------------------------------------------------------------------
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);

-----------------------------------------------------------------------------------------------------------------------------------
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...");
                            }
                   }  
              }   
      };

-----------------------------------------------------------------------------------------------------------------------------------
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。

   
-----------------------------------------------------------------------------------------------------------------------------------
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);
            }
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