Design of real-time periodic control systems through synchronisation and fixed priorities

Control systems are often designed using a set of cooperating periodic modules running under control of a real-time operating system. A correct behaviour of the closed-loop controller requires that the system meets timing constraints like periods and latencies, which can be expressed as deadlines. The software uses the fixed priority based preemption service of the operating system. Latencies are controlled through precedence constraints and more or less tight synchronisation between modules. Such a system can be modelled with timed event graphs, and its temporal behaviour can be analysed using the underlying (max,plus) algebra. Examples coming from a uni-processor robot controller are provided