On the necessity of on-line-BIST in safety-critical applications-a case-study

This paper analyzes the effect of dormant faults on the mean time to failure (MTTF) of highly reliable systems. The analysis is performed by means of Markov models that allow quantifying the effect of dormant faults and other vital reliability parameters. It turns out that the presence of dormant faults can drastically reduce the MTTF of a system, particularly if the operating system allows a sporadic ("event-driven") change from a regular mode of operation to another mode. Virtually every practical system involves such a change, at least in case of emergency. It is demonstrated that on-line built-in self-test (BIST) is an effective means to overcome the deteriorating effect of dormant faults and re-establish a high MTTF. A very moderate test period may already be sufficient. The analysis Is performed for the example of a fail-silent communication system for safety-critical real-time applications.