Worst Case Execution Time Estimation for Control Code of Automation Systems

Control code in automation systems is scheduled to run with tasks with a pre-defined execution order. Tasks, in turn, are connected to Program Organization Units (POUs) implemented in compliance with languages defined by the IEC 61131-3 standard. The execution order of tasks can be accurately determined if the worst-case execution time of the tasks are known a priori. We propose an algorithm for estimation of Worst Case Execution Time (WCET) of control code statically, in a platform-independent way, mainly based on the control flow structure of the code. We use abstract interpretation based techniques to estimate worst case bounds of execution of loops in the code and add minimal platform related parameters to tighten our bounds. Our results on several domain-specific examples have been able to yield good estimates of WCET.