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Determining the worst-case reaction time of IEC 61499 function blocks

The IEC 61499 is an international standard for describing industrial process-control systems. Such systems typically consist of embedded computers that interact closely with physical processes within a feedback loop. In order to correctly control these physical processes, computations in response to inputs need to be done in a timely manner. A program's worst-case reaction time (WCRT) to inputs is usually used to ensure that timing constraints are met. Unfortunately, the standard has no provisions for specifying real-time constraints. Moreover, typical implementations of IEC 61499 are tightly coupled to their runtime environments—each with possibly different semantics and temporal properties—which makes it difficult to automate the estimation of their WCRTs. We propose to adopt a synchronous model for IEC 61499 programs. This allows the programs to be executed without the need of a run-time environment. Consequently, we are able to use a novel model-checking technique to estimate the WCRT of IEC 61499 programs. Experimental results on a suite of programs show that this approach provides conservative estimates that are, on average, less than 10 percent off from the actual WCRT.