Floating-priority storage control for processors in a multi-processor

Abstract

The disclosure describes a floating-priority storage access control arrangement for plural processors to a shared main storage in a multi-processing (MP) system. The shared main storage logically couples the main storage units provided with each of the processors into a single expanse of real addresses available to each processor. Exclusive access to the shared storage is given to any processor for as long as that processor can provide a burst of one or more successive storage requests. The burst ends when that processor misses a storage cycle by not providing a locally granted request. The shared storage access is controlled in each processor by means of an MP priority pointer circuit which receives storage requests granted by a local priority circuit in the processor. The MP priority pointer circuits are interconnected between the processors. When a burst ends for one processor, another processor having one or more pending storage requests is given priority and begins its burst during the missed cycle, continuing with highest priority until it completes its burst by not having a locally granted request during a cycle. If no processor makes a request during a storage cycle, and both processors simultaneously make a request during a following cycle, priority for an access burst is given to the processor which last had priority. Thus, priority flip-flops back and forth between the processors as they respectively access main storage in bursts of requests.