Electronic computer system with means for issuing a non-store request

Abstract

In a computer system of a microprogram control type which processes a succession of instructions to produce a succession of store data units and a succession of store requests under control by a microprogram controller, the store data units being written into a memory by control of a memory controller according to the store requests, a specific one of the instructions being retried from a checkpoint on occurrence of an error during current processing of the specific instruction, the microprogram controller controls execution of a state transition which results in cancellation of the checkpoint on occurrence of the state transition during processing the specific instruction. In order to enable execution of the state transition without waiting for completion of writing previous store data units into the memory according to the store requests issued prior to the occurrence of the state transition, the microprogram controller comprises a control program for producing a non-store imitative request in place of the store request and an imitative store data unit and then producing an indication for executing the state transition. On occurence of the error, the memory controller produces a retry request in absence of the non-store store request and produces a system down signal in the presence of the non-store request.