Master-slave cache system with de-coupled data and tag pipelines and

Abstract

A cache system has a large master cache and smaller slave caches. The slave caches are coupled to the processor's pipelines and are kept small and simple to increase their speed. The master cache is set-associative and performs many of the complex cache management operations for the slave caches, freeing the slaves of these bandwidth-robbing duties. The master cache has a tag pipeline for accessing the tag RAM array, and a data pipeline for accessing the data RAM array. The tag pipeline is optimized for fast access of the tag RAM array, while the data pipeline is optimized for overall data transfer bandwidth. The tag pipeline and the data pipeline are bound together for retrieving the first sub-line of a new miss from the slave cache. Subsequent sub-lines only use the data pipeline, freeing the tag pipeline for other operations. Bus snoops and cache management operations can use just the tag pipeline without impacting data bandwidth. Loop-back flows are performed which cancel an intervening flow in the tag pipeline when the index portions of the addresses match.