Design and evaluation of flexible time-triggered task schedulers for dynamic control applications

A statically-scheduled time-triggered (TT) software architecture demonstrates very predictable patterns of temporal behaviour and is – therefore – widely considered to be an appropriate platform for many high integrity and safety-critical embedded applications. However, there remains an important class of highly dynamic control systems for which it is considered that TT architectures are not a good match and for which the use of ―event triggered‖ (ET) designs is usually preferred. These applications include the control systems for internal combustion engines, brushless DC motors and synchronous AC motors. The aim of the research project presented in this thesis was to explore ways in which a static TT architecture could be adapted in order to better meet the requirements of such highly-dynamic control systems. The project had three main outcomes. The first project outcome was that a novel ―flexible TT architecture was developed. This architecture differs significantly from conventional TT designs in that – during the system operation – only the timing of the next system interrupt is known in advance (that is, the timing of subsequent interrupts is unknown). This allows for considerable flexibility in the task scheduling while retaining most of the features that make static TT approaches attractive. The second project outcome was that two novel schedulers were designed and implemented, in order to demonstrate (by means of an ―existence proof‖) that it was possible to construct a practical implementation of the flexible TT architecture. The third outcome from this project was that a comprehensive evaluation of the flexible TT architecture and the associated scheduler implementations was carried by means of two representative case studies. The case studies involved engine synchronisation and control of a brushless DC motor (BLDCM). In the engine synchronisation case study, the flexible TT architecture was shown to be a viable alternative to ET in conditions where a static TT was unable to cope with the system demands. In the BLDCM case study, while both static TT and flexible TT were viable alternatives, the flexible TT was able to provide similar levels of performance to the static TT solution at a fraction of the resource usage.