Robert A French

US Patent:

58601058, Jan 12, 1999

Filed:

Nov 13, 1995

Appl. No.:

8/557977

Inventors:

Mark W. McDermott - Austin TX
Robert W. French - Austin TX
Antone L. Fourcroy - Ft. Collins CO
Mark E. Burchfield - Austin TX
Xiaoli Y. Mendyke - Plano TX

Assignee:

National Semiconductor Corporation - Santa Clara CA

International Classification:

G06F 1200

US Classification:

711135

Abstract:

An NDIRTY cache line lookahead technique is used to expedite cache flush and export operations by providing a mechanism to avoid scanning at least some cache lines that do not contain dirty data (and therefore will not have to be exported). The exemplary cache organization uses one-line lookahead where each cache line but the last has associated with it an NDIRTY bit that indicates whether the next cache line contains dirty data. For cache flush and export operations, when a cache line (N) is read to check for dirty data that must be exported, the NDIRTY bit for that cache line is also tested to determine whether the next cache line (N+1) contains dirty data--if the NDIRTY bit is clear, indicating that the next cache line is clean, then that line is skipped and the scan proceeds with the line after that (N+2). This exemplary one-line lookahead implementation is readily extendible to N-line lookahead. The cache line lookahead technique reduces the number of cache line accesses required during flush/export operations, with the attendant advantages of reduced flush/export penalty cycles and power, thereby improving overall system performance.