Android電力情報

1.バッテリーの電力管理
Androidの電力量はFramework層で放送メッセージとして発表され、発表者はBatteryServicesである.java. BatteryServiceの原理は、UeventObserverの一例を用いてkernel層の電力量の変化を監視するイベントである.電力の駆動ファイルはすべて/sys/class/power_に置かれています.supplyディレクトリの下には、電圧、電力量パーセント、AC/USB状態などの情報が含まれています.JNIファイルcom_android_server_BatteryService.cppは/sys/class/power_supplyのすべての情報はBatteryServicesに更新されます.JAvaで

static void android_server_BatteryService_update(JNIEnv* env, jobject obj)
{
    setBooleanField(env, obj, gPaths.acOnlinePath, gFieldIds.mAcOnline);
    setBooleanField(env, obj, gPaths.usbOnlinePath, gFieldIds.mUsbOnline);
    setBooleanField(env, obj, gPaths.batteryPresentPath, gFieldIds.mBatteryPresent);
    
    setIntField(env, obj, gPaths.batteryCapacityPath, gFieldIds.mBatteryLevel);
    setVoltageField(env, obj, gPaths.batteryVoltagePath, gFieldIds.mBatteryVoltage);
    setIntField(env, obj, gPaths.batteryTemperaturePath, gFieldIds.mBatteryTemperature);
    
    const int SIZE = 128;
    char buf[SIZE];
    
    if (readFromFile(gPaths.batteryStatusPath, buf, SIZE) > 0)
        env->SetIntField(obj, gFieldIds.mBatteryStatus, getBatteryStatus(buf));
    else
        env->SetIntField(obj, gFieldIds.mBatteryStatus,
                         gConstants.statusUnknown);
    
    if (readFromFile(gPaths.batteryHealthPath, buf, SIZE) > 0)
        env->SetIntField(obj, gFieldIds.mBatteryHealth, getBatteryHealth(buf));

    if (readFromFile(gPaths.batteryTechnologyPath, buf, SIZE) > 0)
        env->SetObjectField(obj, gFieldIds.mBatteryTechnology, env->NewStringUTF(buf));
}

BatteryServiceは、電力情報をブロードキャスト形式で配信

    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
                | Intent.FLAG_RECEIVER_REPLACE_PENDING);

        int icon = getIcon(mBatteryLevel);

        intent.putExtra(BatteryManager.EXTRA_STATUS, mBatteryStatus);
        intent.putExtra(BatteryManager.EXTRA_HEALTH, mBatteryHealth);
        intent.putExtra(BatteryManager.EXTRA_PRESENT, mBatteryPresent);
        intent.putExtra(BatteryManager.EXTRA_LEVEL, mBatteryLevel);
        intent.putExtra(BatteryManager.EXTRA_SCALE, BATTERY_SCALE);
        intent.putExtra(BatteryManager.EXTRA_ICON_SMALL, icon);
        intent.putExtra(BatteryManager.EXTRA_PLUGGED, mPlugType);
        intent.putExtra(BatteryManager.EXTRA_VOLTAGE, mBatteryVoltage);
        intent.putExtra(BatteryManager.EXTRA_TEMPERATURE, mBatteryTemperature);
        intent.putExtra(BatteryManager.EXTRA_TECHNOLOGY, mBatteryTechnology);
        intent.putExtra(BatteryManager.EXTRA_INVALID_CHARGER, mInvalidCharger);

        if (false) {
            Slog.d(TAG, "level:" + mBatteryLevel +
                    " scale:" + BATTERY_SCALE + " status:" + mBatteryStatus +
                    " health:" + mBatteryHealth +  " present:" + mBatteryPresent +
                    " voltage: " + mBatteryVoltage +
                    " temperature: " + mBatteryTemperature +
                    " technology: " + mBatteryTechnology +
                    " AC powered:" + mAcOnline + " USB powered:" + mUsbOnline +
                    " icon:" + icon  + " invalid charger:" + mInvalidCharger);
        }

        ActivityManagerNative.broadcastStickyIntent(intent, null);
    }

傍受を登録すれば

Intent.ACTION_BATTERY_CHANGED

のブロードキャストですべてのバッテリステータス情報を取得できます