Data received before coherency window for a snoopy bus

Abstract

Where a null response can be expected from devices snooping a load operation, data may be used by a requesting processor prior to the coherency response window. A null snoop response may be determined, for example, from the availability of the data without a bus transaction. The capability of accelerating data in this fashion requires only a few simple changes in processor state transitions, required to permit entry of the data completion wait state prior to the response wait state. Processors may forward accelerated data to execution units with the expectation that a null snoop response will be received during the coherency response window. If a non-null snoop response is received, an error condition is asserted. Data acceleration of the type described allows critical data to get back to the processor without waiting for the coherency response window.