Schedulability Analysis of Periodic Tasks Implementing Synchronous Finite State Machines

Model-based design of embedded systems using Synchronous Reactive (SR) models is among the best practices for software development in the automotive and aeronautics industry. The correct implementation of an SR model must guarantee the synchronous assumption, that is, all the system reactions complete before the next event. This assumption can be verified using schedulability analysis, but the analysis can be quite challenging when the system also consists of blocks implementing finite state machines, as in modern modeling tools like Simulink and SCADE. In this paper, we discuss the schedulability analysis of such systems, including the applicability of traditional task analysis methods and an algorithmic solution to compute the exact demand and request bound functions. In addition, we define conditions for computing these functions using a periodic recurrent term, even when there is no cyclic recurrent behavior in the model.