USB----调用过程和简单解释

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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

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