Proper way to close a USB accessory connection

android usb adk accessory
Ytai picture Ytai · Nov 26, 2011 · Viewed 7.3k times · Source

What is the proper way to close a connection to a UsbAccessory in Android? It seems the even in the stock Google example, if I connect and accessory, exit the app and then go back to it, the connection is not re-established.

Looking closely, it seems that after calling close() on the FileDescriptor, it won't open again, and a "could not open /dev/usb_accessory" log is emitted. NOT calling close() is a bad option, as a thread blocking on read() will not be released. Upon physical disconnection / reconnection of the device everything is OK.

It seems really surprising that the simple use-case of exiting the app and then opening it again does not work in the reference application and even more surprising if it is not feasible.

I'm using a Nexus S running stock Android 2.3.6.

Answer

Ytai picture Ytai · Nov 27, 2011

The problem is that the reading thread never exits, thus the file descriptor stays open, and cannot be opened again when the app is resumed.

This has been confirmed to be a bug: http://code.google.com/p/android/issues/detail?id=20545

Vote on this bug if you care about it.

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