Applying the handler-based execution model to IEC 61499 basic and composite function blocks

Abstract

We defined the so-called "handler-based execution model" as a real-time capable execution model for CNet [H. Wurmus, 2002] [N. Hagge and B. Wagner, 2005]. Traditional controller implementations typically consist of big loops with a fix sequential execution scan order. This was not appropriate for Petri-net based CNet that is characterized by a high degree of concurrency and locality. Our execution model is purely based on events to dynamically schedule the evaluation of firing conditions and avoids unnecessary calculations. There are no global event queues. Event-flow is handled locally which is beneficial for multithreaded and/or distributed platforms. This execution model is part of a full automatic code generator that translates CNet controller models into (real-time) Java code. Examining IEC 61499 revealed that function blocks networks similarly feature concurrency and locality, but that execution environments for function blocks are still developed based on traditional fixed sequential scan approaches. This paper will introduce the main concepts of the "Handler- based execution model" and show its possible application to IEC 61499 function blocks for automatic code generation.