A Technique to Analyze the Tolerance to Transient Overloads of a Fault-Tolerant Real-Time System

Fault-tolerance and real-time computing have been traditionally considered as different domains. However, missing deadlines is a fault in a real-time system. In order to build fault free real-time systems, a real-time fault-tolerant architecture based on a Redundancy eXecutive (RX) is presented. The timing properties of such an executive are predictable. On this basis, a technique, based on fixed priority schedulability analysis, for predicting the temporal behaviour of a system is provided. Moreover, this analysis can be applied to hard and soft real-time systems that present bounded transient overloads. In these systems the number of missed deadlines over a given period of time is bounded. The architecture, together with a dual time-out scheme, masks both value errors and timing errors. Thus, providing a feasible mechanism for achieving fault-tolerance for both the functional aspects and the timing aspects. Its application leads to cost-effective systems because the resources do not have to be sized for the worst case and, moreover, the response times are sometimes better than in the non-fault-tolerant equivalent system. I