ENGINEERING A HARD REAL-TIME SYSTEM - FROM THEORY TO PRACTICE

More and more programmers find their software being used in performance critical applications. Unfortunately, they have limited techniques at their disposal to help guarantee this particular aspect of their programs. There has been considerable activity in recent years on developing analysis techniques for hard real-time systems. Inevitably these techniques make simplifying assumptions so as to reduce the complexity of the problem to be solved. For example hard real-time schedulability analysis techniques often assume that the timing properties of the underlying kernel can be accounted for by incorporating extra execution time into the application tasks. Furthermore, they assume that the application task structure is very simple and uniform. This paper considers the implications of using these techniques in the analysis of a typical single processor application, the attitude and orbital control system (AOCS) for the Olympus satellite. The paper outlines a common approach for estimating the response times for tasks, and then extends the scheduling equations so that they can be used in the engineering of realistic real-time systems.