High speed memory cloner with extended cache coherency protocols and responses

摘要

A data processing system comprising a coherency protocol that indicates and updates a coherency state of all data lines within said memory subsystem, and responsive to a naked write operation to a memory location containing a modified copy of data, changes the coherency state of the memory location from modified (M) to invalid (I) without initiating a push of the data to a corresponding address location of main memory. Included within the coherency protocol are specific group of responses for dealing with a naked write request that is received at a memory controller. These responses include: (1) issuing a retry response when the memory controller is unable to allocate a buffer for the write data operation and data at said memory location is not in an M state; (2) issuing a Null response when the memory controller is able to allocate the buffer; and (3) issuing a combined Ack_Resend response when the data at the memory location transitions from an M state to an I state. The Ack_Resend response indicates that the coherency state transition has occurred but the memory controller is not yet able to allocate a buffer to the write operation. The protection of the memory location is transferred to the memory cloner when a combined response is received at the memory cloner for a particular naked write operation.