Direct access mode for a cache

(12) United States Patent

Rowlands et al.

US006732234B1

(io) Patent No.: US 6,732,234 Bl (45) Date of Patent: May 4,2004

(54) DIRECT ACCESS MODE FOR A CACHE

(75) Inventors: Joseph B. Rowlands, Santa Clara, CA (US); Michael P. Dickman, San Jose, CA (US)

(73) Assignee: Broadcom Corporation, Irvine, CA (US)

( * ) Notice: Subject to any disclaimer, the term ol this patent is extended or adjusted under 35 U.S.C. 154(b) by 125 days.

(21) Appl. No.: 09/633,544

(22) Filed: Aug. 7, 2000

(51) Int. CI.7 G06F 12/00

(52) U.S. CI 711/117; 711/118; 711/128;

711/133; 711/136; 711/145; 711/702; 711/108;

711/119

(58) Field of Search 711/117, 118,

711/128, 133, 160, 136, 139, 145; 702/108,

119

(56) References Cited

U.S. PATENT DOCUMENTS

A cache is configured to receive direct access transactions. Each direct access transaction explicitly specifies a cache storage entry to be accessed in response to the transaction. The cache may access the cache storage entry (bypassing the normal tag comparisons and hit determination used for memory transactions) and either read the data from the cache storage entry (for read transactions) or write data from the transaction to the cache storage entry (for write transactions). The direct access transactions may, for example, be used to perform testing ol the cache memory. As another example, direct access transactions may be used to perform a reset ol the cache (by writing known data to each cache entry). In embodiments employing error checking and correction (ECC) mechanisms, direct access write transactions could also be used to recover from uncorrectable ECC errors, by overwriting the lailing data to eliminate the errant data. In one embodiment, the cache may alter the state ol its replacement policy in response to a direct access transaction explicitly specilying a particular way ol the cache.

40 Claims, 13 Drawing Sheets

Page 2

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