On the scheduling of flexible and reliable real-time control systems

Many real-time systems, such as manufacturing plants, have long life cycles. To enable the realization of technological innovations and to mitigate the risk and cost of bringing new control technologies into functioning systems, flexible and reliable real-time software architectures such as Simplex have been developed. There is also an emerging trend that integrates the design of controllers and schedulers. For example, algorithms that identify the optimal frequencies of control tasks subject to schedulability constraints have been developed, and the notion of feedback schedulers has been investigated. However, the optimization of the performance of flexible and reliable architectures with analytically redundant software controllers has remained an open problem. In fact, a direct application of the existing optimization methods would not yield the optimal frequencies. In this paper, we present a method that correctly finds the optimal frequencies for systems using analytically redundant controllers. We also show that the proposed method is robust against inaccuracies in the estimation of failure rates of the controllers.