Patent ID: 7194583

Claim:
A host controller comprising: a descriptor fetch unit adapted to send out requests for descriptors and receive descriptors in reply to said requests, said descriptors being data structures for describing attributes of the data transfer to and from devices controlled by said host controller; and a descriptor cache adapted to store prefetched descriptors, wherein said descriptor cache is arranged to store periodically scheduled descriptors and asynchronously scheduled descriptors, wherein said descriptor cache is adapted to let said periodically scheduled descriptors expire at frame boundaries, wherein said descriptor cache is further adapted to store individual replacement control values for at least a part of the stored prefetched descriptors, wherein each said replacement control value is a sympathy value indicative of the usefulness of storing the respective descriptor in said descriptor cache, wherein said descriptor fetch unit is adapted to calculate said sympathy value and wherein said descriptor fetch unit is connected to said descriptor cache to write the calculated sympathy value into said descriptor cache, and wherein the host controller is arranged to replace a stored prefetched descriptor in said descriptor cache by a newly prefetched descriptor based on the replacement control value associated with the stored prefetched descriptor.