[beagleboard] USB can not wakeup


I use a usb hub to connect to a beagleboard, and plug in a thumb drive on the hub. It works fine.
But when i remove the thumb drive and plug in again after 2 minutes, the thumb drive can not work,
I use dmesg to print out the message. I found a message “suspend root hub”, seems that the root hub doesn’t wake up when i plug in the thumb drive at the second times.

Is there anyone who has encountered the same problem before? And can you please share with me how you solved this problem. thanks.