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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)

posted on 2010-09-15 11:29  arm-linux  阅读(3425)  评论(0编辑  收藏  举报