Android中的BatteryService及相关组件 

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文章出处：http://www.limodev.cn/blog


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);
            }