I'm trying to add USB hub support to an Atmel microcontroller with USB host. I was able to get the hub to enumerate as well as a second device attached to the hub. When I detach the latter device, the host gets notified (via the status change interrupt endpoint) but I get a halt condition when trying to send a Get Port Status and can't figure out why. What could be possible causes and is there anything that should be done between receiving the interrupt IN transfer and sending a control transfer?