Android Battery 分析

一、 Android uevent架构

 

Android很多事件都是通过 uevent跟 kernel来异步通信的。其中类 UEventObserver是核心。 
UEventObserver接收 kernel的 uevent信息的抽象类。 

1、 server层代码 
1)battery server:
frameworks/frameworks/base/services/java/com/android/server/SystemServer.java
frameworks/frameworks/base/services/java/com/android/server/BatteryService.java

2、 java层代码 
frameworks/base/core/java/android/os/UEventObserver.java

3、 JNI层代码 
frameworks/base/core/jni/android_os_UEventObserver.cpp

4、底层代码 
hardware/libhardware_legacy/uevent/uevent.c
读写 kernel的接口 socket(PF_NETLINK, SOCK_DGRAM, NETLINK_KOBJECT_UEVENT);

二、 UEventObserver的使用

类 UEventObserver提供了三个接口给子类来调用： 
1、 onUEvent(UEvent event)
子类必须重写这个 onUEvent来处理 uevent。 
2、 startObserving(String match)
启动进程，要提供一个字符串参数。 
3、 stopObserving()
停止进程。 

例子： 
//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。

 

三、 vold server分析 

1、在 system/vold/NetlinkManager.cpp中： 

if ((mSock = socket(PF_NETLINK,SOCK_DGRAM,NETLINK_KOBJECT_UEVENT)) < 0) {
SLOGE("Unable to create uevent socket: %s", strerror(errno));
return -1;
}
if (setsockopt(mSock, SOL_SOCKET, SO_RCVBUFFORCE, &sz, sizeof(sz)) < 0) {
SLOGE("Unable to set uevent socket options: %s", strerror(errno));
return -1;
}
if (bind(mSock, (struct sockaddr *) &nladdr, sizeof(nladdr)) < 0) {
SLOGE("Unable to bind uevent socket: %s", strerror(errno));
return -1;
}

2、然后在 system/vold/NetlinkHandler.cpp的 NetlinkHandler::onEvent中处理

void NetlinkHandler::onEvent(NetlinkEvent *evt) {
VolumeManager *vm = VolumeManager::Instance();
const char *subsys = evt->getSubsystem();
if (!subsys) {
SLOGW("No subsystem found in netlink event");
return;
}
if (!strcmp(subsys, "block")) {
vm->handleBlockEvent(evt);
} else if (!strcmp(subsys, "switch")) {
vm->handleSwitchEvent(evt);
} else if (!strcmp(subsys, "battery")) {
} else if (!strcmp(subsys, "power_supply")) {
}
}

3、在 system/core/libsysutils/src/NetlinkListener.cpp中监听。 


四、 battery server分析

 

java代码： 
frameworks/frameworks/base/services/java/com/android/server/BatteryService.java

JNI代码： 
frameworks/base/services/jni/com_android_server_BatteryService.cpp

 

1、 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);

2、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”

3、数据传送

BatteryService主动把数据传送给所关心的应用程序，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);

 

4、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…”);
}
}
}
};

5、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。

 

 http://blog.csdn.net/ericyelai/article/details/6221308