Digital Equipment Corporation

Richard C Beaven

Tryggve Fossum

Ricky C Hetherington

Ronald M Salett

John E Murray

Michael B Evans

William R Grundmann

In a multiprocessor system, an error occurring in any one of the CPUs may have an impact upon the operation of the remaining CPUs, and therefore these errors must be handled quickly. The errors are grouped into two categories: synchronous errors (those that must be corrected immediately to allow continued processing of the current instruction); and asynchronous errors (those errors that do not affect execution of the current instruction and may be handled upon completing execution of the current instruction). Since synchronous errors prevent continued execution of the current instruction, it is preferable that the last stable state conditions of the faulting CPU be restored and the faulting instruction reexecuted. These stable state conditions advantageously occur between the execution of each instruction. However, in a pipelined computer system, it is difficult to identify the beginning and ending of a selected instruction since multiple instructions are in process at the same time. Accordingly, the execution unit is selected to be the point of synchronization between error handling and instruction execution. Once the error is indentified as asynchronous or synchronous and the execution unit allows the instruction to complete or rolls back the state conditions to their preinstruction values, error analyzing software examines the condition of the suspect data latches in the CPU. A serial diagnostic link stops the system clock of the CPU and serially loads the CPU data latches into the System Processor Unit for error determination. Thereafter, the CPU system clock is restarted and the CPU resumes execution.

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Sudbury, MA, United States of America

Richard C Beaven