Dynamic management of snoop granularity for a coherent asynchronous DMA cache

摘要

A system and method dynamically changes the snoop comparison granularity between a sector and a page, depending upon the state (active or inactive) of a direct memory access (DMA) I/O device which is writing to a device on the system bus asynchronously when compared to the CPU clock. By using page address granularity, erroneous snoop hits will not occur, since potentially invalid sector addresses are not used during the snoop comparison. Sector memory addresses may be in a transition state at the time when the CPU clock determines a snoop comparison is to occur, because this sector address has been requested by a device operating asynchronously with the CPU clock. Once the asynchronous device becomes inactive the system dynamically returns to a page and sector address snoop comparison granularity.