Abstract: An interface between a storage unit and a system control unit maintains a sequential processing when retrying linestores by providing a single piece of information that the linestore is a "first" in a series. An initial request flag accompanies linestore requests to the system controller and is returned to the storage unit with linestore replies. A mode indicator coupled with the storage unit pipeline sets a retry mode latch in response to a linestore restart reply, and resets the retry mode latch in response to a linestore read reply by the system controller to an initial request. Logic in the pipeline suppresses requests for the system resource in the pipeline, other than initial requests, when the retry mode latch is set, such as by flagging data subject of the second flow as locked or otherwise invalid. The port includes a state machine which preserves the order of pending requests for the system resource.

Abstract: In a multiprocessor system with an interleaved memory, predicted busy terms for interleaves of the main store being accessed are sent to each processor in the system, so that they will not waste pipe flows making requests to the busy interleaves. The predicted busy term is lowered before access to the interleaves is complete, to allow for the latency between the time the processor sets up the request and the time the main store system receives it. Contention occurs when several processors request access to the same interleave of main store. To detect deadlocks, a counter for each processor keeps track of the number of consecutive requests from that processor which have been rejected. Once the number reaches a threshold for a first processor, its counter initiates a state machine which inhibits other processors from making requests to the main store until the first processor is successful in gaining access.