Patent ID: 9086975
Filing Date: 2015-07-21
Classification: G06F

Abstract:
1. A method of data processing, comprising: receiving, at a coherent attached processor proxy (CAPP) of a primary coherent system, a memory access request from an attached processor (AP) external to the primary coherent system, wherein the CAPP includes a CAPP directory of contents of a cache memory in the AP that holds copies of memory blocks belonging to a coherent address space of the primary coherent system, and wherein the receiving includes receiving an expected coherence state of a target address of the memory access request with respect to the cache memory of the AP; in response to receiving the memory access request at the CAPP, the CAPP determining a coherence state of the target address with respect to the CAPP and determining whether or not the expected coherence state matches the coherence state determined by the CAPP; in response to determining that the expected coherence state matches the coherence state determined by the CAPP, the CAPP issuing, on behalf of and in stead of the AP, a memory access request corresponding to that received from the AP on a system fabric of the primary coherent system; and in response to determining that the expected coherence state does not match the coherence state determined by the CAPP, the CAPP transmitting a failure message to the AP without issuing on the system fabric a memory access request corresponding to that received from the AP.