Scheduling of Time-Triggered Real-Time Systems

Abstract

This paper introduces a new class of applications for constraint programming. This new type of application originates out of a special class of real-time systems, enjoying increasing popularity in areas such as automotive electronics and aerospace industry. Real-time systems of this kind are time triggered in the sense that their overall behavior is globally controlled by a recurring clock tick. Being able to compute an appropriate pre-runtime schedule automatically is the major challenge for such an architecture. What makes this specific off-line scheduling problem somewhat untypical is that a potentially indefinite, periodic processing has to be mapped onto a single time window. In this article we will show how this problem can be solved by constraint programming and we will describe which techniques from traditional scheduling and real-time computing led to success and which failed when confronted with a large-scale application of this type. The techniques that proved to be the most successful were special global constraints and an elaborate search heuristics from Operations Research. Also for finding a valid schedule mere serialization is shown to be sufficient. The actual implementation was done in the concurrent constraint programming language Oz.