Non-inclusive cache method using pipelined snoop bus

摘要

A non-inclusive cache system includes an external cache and a plurality of on-chip caches each having a set of tags associated therewith, with at least one of the on-chip caches including data which is absent from the external cache. A pipelined snoop bus is ported to each of the set of tags of the plurality of on-chip caches and transmits a snoop address to the plurality of on-chip caches. A system interface unit is responsive to a received snoop request to scan the external cache and to apply the snoop address of the snoop request to the pipelined snoop bus. A plurality of response signal lines respectively extend from the plurality of on-chip caches to the system interface unit, each of the signal lines for transmitting a snoop response from a corresponding one of the on-board caches to the system interface unit. The set of tags can be implemented by dual-porting the cache tags, or by providing a duplicate and dedicated set of snoop tags.