In one embodiment, a data processing system includes, but is not limited
to, a processor, a memory coupled to the processor, and a universal
serial bus (USB) controller coupled to the processor and the memory. The
USB controller includes a local memory to cache at least one activity
descriptor of at least a portion of a periodic schedule having multiple
frames stored in the main memory. The USB controller defers to service an
active USB device described by one of the activity descriptors until a
corresponding frame is scheduled to be serviced subsequently. Other
methods and apparatuses are also described.