USB----调用过程和简单解释

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我是靠谱客的博主欣慰茉莉，最近开发中收集的这篇文章主要介绍USB----调用过程和简单解释，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

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