Speculative Fetch Memory Protocol Method
Original Publication Date: 2002-May-02
Included in the Prior Art Database: 2003-Jun-21
This disclosure describes a Speculative Fetch protocol for a command response interface between a memory requester and a central storage memory controller of a computer memory subsystem that 1) improves the utilization of the bidirectional data bus between them, and 2) improves the utilization of fetch resources, while not adding any additional latency to a memory access. The protocol allows the memory requester to either 1) acquire requested data or not and 2) in the case where data is not acquired, to re-use a memory controller fetch resource before the current operation being processed by that resource has completely ended. In a highly pipelined memory subsystem with a distributed L2 cache, in order to minimize the access time required to obtain data from central storage when it is not found in the local L2 cache (cache miss), the memory requester will initiate a directory search of the remote L2 caches, while simultaneously initiating a fetch access to central storage for the data.