METHOD FOR DIRECT MEMORY ACCESS BLOCK MOVEMENT USING DESCRIPTOR PREFETCH, DIRECT MEMORY ACCESS DEVICE, AND DATA PROCESSING SYSTEM

摘要

PROBLEM TO BE SOLVED: To provide a DMA device prefetching descriptors into a descriptor prefetch buffer. SOLUTION: The size of the descriptor prefetch buffer holds an appropriate number of descriptors for a given latency environment. To support a linked list of descriptors, sequential descriptors are prefetched, and descriptors contrary to them are discarded. A DMA engine 412 keeps the descriptor prefetch buffer full by requesting multiple descriptors per transaction whenever possible. A bus engine 414 fetches these descriptors from a system memory 430 and writes them in the prefetch buffer. The DMA engine may use an aggressive prefetch where the bus engine requests the maximum number of descriptors that the buffer supports when there is any space in the descriptor prefetch buffer. COPYRIGHT: (C)2008,JPO&INPIT