Real-time computers are often used in embedded, life-critical applications where high reliability is important. A common approach to making such systems dependable is to vote on redundant processors executing multiple copies of the same task is described. The processors which make up such voted systems are subjected not only to independently occurring permanent and transient failure, but also to correlated transients brought about by electromagnetic interference from the operating environment. To counteract these transients, checkpointing and time redundancy are required, in addition to processor redundancy. This work analyzes the use of time and device redundancy in systems subject to correlated failure. The tradeoffs in checkpoint placement in such a system are found to be considerably different from those for non-redundant systems without real-time constraints. The authors compare fault-tolerant designs and without a rollback capability, accounting for the increased hardware-failure rate due to processor duplication when faults are detected in hardware, and the doubled execution times when detection is implemented in software.
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