Terminating barriers in streams of access requests to a data store while maintaining data consistency

摘要

A memory controller for a slave memory that controls an order of data access requests is disclosed. There is a read and write channel having streams of requests with corresponding barrier transactions within the request streams indicating where reordering should not occur. The controller has barrier response generating circuitry located on the read and said write channels and being responsive to receipt of one of said barrier transactions: to issue a response to the received barrier transaction such that subsequent requests in said stream of requests are not blocked by the barrier transaction and can be received and to terminate the received barrier transaction and not transmit the received barrier transaction further; and to mark requests subsequent to the received barrier transaction in the stream of requests with a barrier context value identifying the received barrier transaction. The memory controller comprises a point of data consistency on the write channel prior to the memory; and the memory controller comprises comparison circuitry configured to compare the bather context value of each write request to be issued to the memory with the barrier context values of at least some pending read requests, the pending read requests being requests received at the memory controller but not yet issued to the memory and: in response to detecting at least one of the pending read requests with an earlier barrier context value identifying a bather transaction that has a corresponding barrier transaction in the stream of requests on the write channel that is earlier in the stream of requests than the write request, stalling the write request until the at least one pending read request has been performed; and in response to detecting no pending read requests with the earlier barrier context value, issuing the write request to the memory.