Silicon Graphics, Incorporated

Mips Computer Systems, Inc.

Elxsi

Allen W Roberts

George S Taylor

Timothy P Layman

P Michael Farmwald

Huy X Ngo

Harold L McFarland, Jr

Timonty S Fu

Harlan Lau

A method of invalidating a line in a designated cache in each level of a multiple level, multiple cache memory system. Each line of the cache memory system includes a tag field, a data field, and a bit indicative of the validity of the line. The method provides a software invalidate instruction which bypasses any address translation mechanism. Included in the software invalidate instruction is a first field to identify within which multiple cache the line is to be avoided. A target address is generated to index each level of the cache memory system. The state of the bit is changed in accordance with the address and the invalidate instruction.

Software invalidation in a multiple level, multiple cache system

A two-level cache memory system for use in a computer system including two primary cache memories, one for storing instruction and one for storing data. The system also includes a secondary cache memory for storing both instructions and data. The primary and secondary caches each employ their own separate tag directory. The primary caches use a virtual addressing scheme employing both virtual tags and virtual addresses. The secondary cache employs a hybrid addressing scheme which uses virtual tags and partial physical addresses. The primary and secondary caches operate in parallel unless the larger and slower secondary cache is busy performing a previous operation. Only if a 'miss' is encountered in both the primary and secondary caches does the system processor access the main memory.

Cache memory system employing virtual address primary instruction and

A two-level cache memory system for use in a computer system including two primary cache memories, one for storing instructions and one for storing data. The system also includes a secondary cache memory for storing both instructions and data. The primary and secondary caches each employ their own separate tag directory. The primary caches use a virtual addressing scheme employing both virtual tags and virtual addresses. The secondary cache employs a hybrid addressing scheme which uses virtual tags and partial physical addresses. The primary and secondary caches operate in parallel unless the larger and slower secondary cache is busy performing a previous operation. Only if a 'miss' is encountered in both the primary and secondary caches does the system processor access the main memory.

Two-level cache memory system

A solution to the problem in differential buses that the bus state for a given line pair is undefined when no unit is driving either of the bus lines in the pair. The lines in the bus pair are terminated to different voltage levels, thereby establishing a desired default condition when no unit is driving either line. The voltage offset between the two bus lines must be sufficient that differential receivers coupled to the bus when the bus is not driven can respond to the offset. At the same time, the offset must not be so great that a driver attempting to drive the bus pair cannot overcome the offset with enough margin for the receivers.

Differential bus with specified default value

In a high speed data bus system, each functional unit has an associated port which operates to accept all related information that makes up a communication, or if this cannot be done, to accept none of the information. More particularly, an information transfer, depending on its nature, may comprise one BIQ or more than one BIQ (a 'BIQ' is a bus information quantum which is placed on the bus for one bus cycle). To implement the indivisibility of multiple-BIQ transfers, the control logic for each port includes screening circuitry responsive to the state of the port's input buffers, and further responsive to flags from the functional unit for selectively accepting or rejecting BIQ's, and further includes screening constraint circuitry to ensure that the port accepts all or none of the BIQ's that make up the transfer. Depending on the flag, the rejection may be total, or may apply only to a designated class of transfers (for example, operations).

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Union City, CA, United States of America

Allen W Roberts