VCOM problem

Hi All,

I have intermittent problem with my VCOM driver. The VCOM driver works as a
serial port to USB converter.
Sometimes the VCOM driver will hang when the system resumes from standby.
The problem can be resolved by plugging a USB device into any of the
remaining USB ports. I am thinking of querying the USB port status in the
system resume routine, and to reset the USB port if the status is abnormal.
Does anyone know how to query the status of the USB port?
Can someone tell me how I can reset the USB port?
Some sample code or reference document would be much appreciated.