Processor and method for delaying the processing of cache coherency

Abstract

A processor and method for delaying the processing of cache coherency transactions during outstanding cache fills in a multi-processor system using a shared memory. A first processor fetches data having a specified address by addressing a cache memory, and when the specified address is not in the cache, saving the specified address in a fill address memory, and sending a fill request to the shared memory. Before return of fill data, the first processor receives a cache coherency request including the specified address from a second processor requesting invalidation of an addressed block of data. The first processor responds by checking whether the fill address memory includes the specified address, and upon finding the specified address in the fill address memory, delaying execution of the cache coherency request until the fill data is returned, and when the fill data is returned, using the fill data without retaining a validated block of the fill data in the cache. In a preferred embodiment, the fill memory is a content-addressable memory including a plurality of entries, and each entry has a fill address, an ownership fill bit (OREAD), an ownership-read invalidate pending bit (OIP), and a read invalidate pending bit (RIP). The OIP or RIP bit is set when execution of a cache coherency request is delayed, and these bits are read upon completion of a fill to execute the delayed request.