Two-level virtual/real set associative cache system and method with

Abstract

A two-level virtual/real cache system, and a method for detecting and resolving synonyms in the two-level virtual/real cache system, are described. Lines of a first level virtual cache are tagged with a virtual address and a real pointer which points to a corresponding line in a second level real cache. Lines in the second level real cache are tagged with a real address and a virtual pointer which points to a corresponding line in the first level virtual cache, if one exists. A translation-lookaside buffer (TLB) is used for translating virtual to real addresses for accessing the second level real cache. Synonym detection is performed at the second level real cache. An inclusion bit I is set in a directory of the second level real cache to indicate that a particular line is included in the first level virtual cache. Another bit, called a buffer bit B, is set whenever a line in the first level virtual cache is placed in a first level virtual cache writeback buffer for updating main memory. When a first level cache miss occurs, the TLB generates a corresponding real address for that page and the first level virtual cache selects a line for replacement and also notifies the second level real cache which line it chooses for replacement. The real address is then used to access the second level real cache. Synonym detection and resolution are performed by the second level real cache.