Least recently used (lru) cache replacement implementation using a fifo storing indications of whether a way of the cache was most recently accessed

Abstract

A method and apparatus for calculating a victim way that is always the least recently used way. More specifically, in an m-set, n-way set associative cache, each way in a cache set comprises a valid bit that indicates that the way contains valid data. The valid bit is set when a way is written and cleared upon being invalidated, e.g., via a snoop address, The cache system comprises a cache LRU circuit which comprises an LRU logic unit associated with each cache set. The LRU logic unit comprises a FIFO of n-depth (in certain embodiments, the depth corresponds to the number of ways in the cache) and m-width. The FIFO performs push, pop and collapse functions. Each entry in the FIFO contains the encoded way number that was last accessed.