An apparatus and method is provided for scheduling USB transaction processing
tasks. A periodic queue head list associated with a USB host controller is configured
to be processed once every polling period. The periodic queue head list describes
a location of the USB transaction processing tasks scheduled for processing. The
entries in a frame list of the USB host controller are linked to identify a corresponding
periodic queue head list. A USB transaction processing task processed by the USB
host controller is assigned to one of the periodic queue head list. A desired response
time for the USB transaction processing task is matched with the polling period
of the periodic queue head list.