Fetching Primary and Redundant Instructions in Turn for a Fault-Tolerant Embedded Microprocessor

With the development of semiconductor technology, microprocessors become more and more susceptible to transient faults. Some proposed schemes support redundant execution of a program in a superscalar processor for fault tolerance. However, they require a huge queue to accommodate interim states, which enlarge the hardware cost significantly. This paper analyzes the effect of halving a processor¿s instruction fetch bandwidth on a program¿s performance. We find that the performance degradation resulted from halving instruction fetch bandwidth declines when instruction latency is lengthened, branch prediction accuracy deteriorates or cache miss rate increases. Since an embedded microprocessor is characterized by long instruction latency, high branch misprediction rate and cache miss rate, a fault-tolerant scheme is proposed, in which two threads fetch instructions in turn and execute in the same processor core simultaneously without any extra queue. The simulation results from eight embedded applications show that performance penalty of our solution ranges from 6.5% to 30.1%, with an average of 22.5%, which is lower than that of the other proposed schemes. The experiment also indicates that our scheme can effectively detect faults occurring in the entire pipeline with short fault detection latency and minimal hardware cost. It is well suited for our solution to realize a reliable embedded microprocessor.