USB----调用过程和简单解释

01）设置包中对mUsbManager的调用

mUsbManager.setCurrentFunction(function, false);

---> frameworks/base/core/java/android/hardware/usb/UsbManager.java

/**
* Sets the current USB function.
* If function is null, then the current function is set to the default function.
*
* @param function name of the USB function, or null to restore the default function
* @param makeDefault true if the function should be set as the new default function
*
* {@hide}
*/
public void setCurrentFunction(String function, boolean makeDefault) {
try {
mService.setCurrentFunction(function, makeDefault);
} catch (RemoteException e) {
Log.e(TAG, "RemoteException in setCurrentFunction", e);
}
}

/*mService 的赋值之处如下*/

    /**
     * {@hide}
     */
    public UsbManager(Context context, IUsbManager service) {
        mContext = context;
        mService = service;
    }

----->frameworks/base/core/java/android/hardware/usb/IUsbManager.aidl

/* Sets the current USB function. */
void setCurrentFunction(String function, boolean makeDefault);

该文件具体实现在如下文件

------->frameworks/base/services/usb/java/com/android/server/usb/UsbService.java

@Override
public void setCurrentFunction(String function, boolean makeDefault) {
mContext.enforceCallingOrSelfPermission(android.Manifest.permission.MANAGE_USB, null);

// If attempt to change USB function while file transfer is restricted, ensure that
// the current function is set to "none", and return.
UserManager userManager = (UserManager) mContext.getSystemService(Context.USER_SERVICE);
if (userManager.hasUserRestriction(UserManager.DISALLOW_USB_FILE_TRANSFER)) {
if (mDeviceManager != null) mDeviceManager.setCurrentFunctions("none", false);
return;
}

if (mDeviceManager != null) {
mDeviceManager.setCurrentFunctions(function, makeDefault);
} else {
throw new IllegalStateException("USB device mode not supported");
}
}

如此，便调到了最常用的类frameworks/base/services/usb/java/com/android/server/usb/UsbDeviceManager.java

public void setCurrentFunctions(String functions, boolean makeDefault) {
if (DEBUG) Slog.d(TAG, "setCurrentFunctions(" + functions + ") default: " + makeDefault);
mHandler.sendMessage(MSG_SET_CURRENT_FUNCTIONS, functions, makeDefault);
}

.........

<pre name="code" class="java">                case MSG_SET_CURRENT_FUNCTIONS:
String functions = (String)msg.obj;
boolean makeDefault = (msg.arg1 == 1);

mSettingUsbCharging = false;
mSettingUsbBicr = false;

/* In BICR evo, it's hard to confirm that the current disconnect is caused by switching usb function or unplugging usb cable*/
/* So add a flag to know it*/
mIsUserSwitch = true;

if (functions != null && functions.equals(UsbManager.USB_FUNCTION_CHARGING_ONLY)) {
mSettingUsbCharging = true;
mCurrentFunctions = removeFunction(mCurrentFunctions, UsbManager.USB_FUNCTION_MTP);
mCurrentFunctions = removeFunction(mCurrentFunctions, UsbManager.USB_FUNCTION_PTP);
updateUsbState();
if (DEBUG) Slog.d(TAG, "handleMessage - MSG_SET_CURRENT_FUNCTION - CHARGING_ONLY - makeDefault: " + makeDefault);
} else if (functions != null && functions.equals(UsbManager.USB_FUNCTION_BICR)) {
mSettingUsbBicr = true;
if (DEBUG) Slog.d(TAG, "handleMessage - MSG_SET_CURRENT_FUNCTION - BICR - makeDefault: " + makeDefault);
} else if (functions == null && mDefaultFunctions.equals(UsbManager.USB_FUNCTION_CHARGING_ONLY)) {
functions = mDefaultFunctions;
mSettingUsbCharging = true;
makeDefault = true;
updateUsbState();
if (DEBUG) Slog.d(TAG, "handleMessage - MSG_SET_CURRENT_FUNCTION - [Tethering Off] USB_FUNCTION_CHARGING_ONLY - makeDefault: " + makeDefault);
}

setEnabledFunctions(functions, makeDefault);

mIsUserSwitch = false;
//ALPS00428998
if(mMtpAskDisconnect) mMtpAskDisconnect = false;
//ALPS00428998

if (DEBUG) Slog.d(TAG, "handleMessage - MSG_SET_CURRENT_FUNCTION - functions: " + functions);
break;

最后有一点说明：

与usb相关的两个系统属性值：'persist.sys.usb.config'和'sys.usb.config'

reboot之后是不是默认的charging模式，主要是看'persist.sys.usb.config'属性值是不是'charging'(或者'charging,adb')，插拔usb线会不会到默认的功能是看'sys.usb.config'属性值是不是'charging'(或者'charging,adb').

也可参详http://blog.csdn.net/lylianlll/article/details/8446675
http://blog.csdn.net/chief1985/article/details/4551242