DMA controller with prefetch cache rechecking in response to memory fetch decision unit's instruction when address comparing unit determines input address and prefetch address coincide

摘要

A computer which can efficiently perform DMA transfer even if the bus on an input/output adapter side is operating at a high speed and the bus on a main memory side is operating at a low speed. In this computer, the DMA controller functions to prefetch the data to the cache from the main memory and is provided with a prefetch address table holding the prefetch address; an address comparing unit which compares the prefetch address and the input address; a hit recheck control unit which judges if there is a hit in the cache again; and a memory fetch decision unit which instructs the hit recheck control unit to perform a hit recheck when the input address is a cache miss (mis-hit) and a comparison of the input address and the prefetch address shows they coincide while makes a read request to the main memory system when it shows they do not coincide.