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Abstract

Methods of maintaining cache coherency of a virtual cache memory system in a data processing system are disclosed. The entries of the virtual cache memory include physical address information and logical address information. A memory access operation may be initiated on one or more predetermined memory locations based on physical address information. A determination may be made if the memory access operation may involve cache coherent memory. If the memory access operation may involve cache coherent memory, then a cache coherency command may be issued that contains physical address information of the memory access operation. Based on the cache coherency command and the physical address information, a determination may be made if there is a match between the physical address information of the memory access operation and the physical address information stored in the virtual cache. If there is a match, then a determination may be made whether data associated with the particular entry of the virtual cache memory is dirty. If the data associated with the particular entry of the virtual cache memory is dirty, then a write back operation may be initiated, and data in the particular entry of the virtual cache memory may be written to memory. A command may then be issued that indicates that the virtual cache memory and the memory locations of the memory access operation are cohered, and the memory access operation may be completed. A determination also may be made whether the memory access operation is a write operation. If the memory access operation is a write operation, then the particular entry of the virtual cache memory may be invalidated. The virtual cache memory may be included in a single chip microprocessor, and a device external to the single chip microprocessor may initiate the memory access operation. A circuit that bridges between the external device and an internal bus may receive a command from the external device to initiate the memory access operation.

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First Claim