Single cycle processor/cache interface

Abstract

An improved interface between a processor and an external cache system, having particular application for use in high speed computer systems. A cache memory for storing frequently accessed data is coupled to a cache address register (CAR). A processor generates addresses which correspond to locations of desired data in the cache, and provides these addresses to the CAR. Upon the receipt of a clock signal, the CAR couples the address to the cache memory. The processor includes a data register for receiving accessed cache data over a data bus. Data is latched into the register upon the receipt of a clock signal. Due to inherent delays associated with digital logic comprising the processor, clock signals provided by an external clock are received by the CAR prior to their receipt by the processor's data register. This delay (a fraction of a clock cycle) provides additional time to access the cache memory before the data is expected on the data bus. The CAR is fabricated out of a technology that allows it to drive the address to the large capacitive load of the cache memory in much less time than the processor itself could drive such a load. Thus, due to this buffering capability of the CAR, the cache can be much larger than what could be supported by the processor itself. The time expended sending the address from the processor to the CAR buffer, which would otherwise not be present if the processor addressed the cache directly from an internal register, does not subtract from the processor cycle time since the processor can compute the cache address and send it to the CAR in less than the time required to access the cache.