PORTS Forum

Ports and Interfaces => USB => Topic started by: jmag999 on July 24, 2014, 10:12:31 am

Title: What causes device to be removed from Device Manager
Post by: jmag999 on July 24, 2014, 10:12:31 am

I have a device that needs to be removed from device manager after a timeout occurs (30 minutes of bus inactivity).  The USB cable is still connected at this point, but the device will go to sleep and stop communicating to conserve battery life.  The user must then unplug and re-plug the usb cable to resume communication.

I have tried powering down the USB peripheral, different pull-up/down options etc..., but the device still remains in device manager.  What causes it to be removed (short of an unplug).

Title: Re: What causes device to be removed from Device Manager
Post by: Jan Axelson on July 24, 2014, 10:27:53 am

If it's low or full speed, emulate detach by removing the pull-up on D+ or D-.

Or see:

http://msdn.microsoft.com/en-us/library/windows/hardware/ff540144%28v=vs.85%29.aspx

Title: Re: What causes device to be removed from Device Manager
Post by: jmag999 on July 24, 2014, 12:14:59 pm

Thanks so much.  I could not find that detail in any of my searching, and sure enough, it works!  Not many devices purposely detach themselves from the host I guess.

Title: Re: What causes device to be removed from Device Manager
Post by: Jan Axelson on July 24, 2014, 05:02:31 pm

I'm not an attorney, but for commercial products, be aware of Cypress patent on emulating detach and re-enumerating.