Android powered device in USB host mode

问题

Android has implemented the USB host mode in Android 3.1 and newer.

I've gone through documents in the following link:

http://developer.android.com/guide/topics/connectivity/usb/index.html

http://developer.android.com/guide/topics/connectivity/usb/host.html

However, the information provided by Android official website is relatively too high level for me to understand the whole story.

I know that OTG is necessary to implement USB host mode.

I have some questions listed in the following:

1. How kernel deals with USB host mode? Does it need to configure any file?

2. How Android enters USB host mode in the low level ?

3. How Android switch between USB host mode and device mode?

4. To turn into this mode, is USB driver needed?

Please let me know if you have any idea about this.

Thanks

来源：https://stackoverflow.com/questions/23511900/android-powered-device-in-usb-host-mode