Apparatus and method for performing write-combining in a pipelined microprocessor using tags

摘要

A tag-based write-combining apparatus in a microprocessor. The apparatus includes a register that stores the store address of the last write-combinable store passing through the store stage of the pipeline. Tag allocation logic compares the last store address with the store address of a new store and allocates the same tag as was previously allocated to the last store if the addresses are in the same cache line, and assigns the next incremental tag otherwise. Tag registers store write buffer tags associated with store data in write buffers waiting to be written to memory on the processor bus. When the new store reaches the write buffer stage, tag comparators compare the new store tag with the write buffer store tags. If the tags match, the write buffer control logic combines the new store data with the store data in the write buffer with the matching tag.