Design Patterns to Support the Migration between Event-Triggered and Time-Triggered Software Architectures

There are two main architectures used to develop software for modern embedded systems: these can be labelled as “event-triggered” (ET) and “time-triggered” (TT). This thesis is concerned with the issues involved in migration between these two architectures. Although TT architectures are widely used in safety-critical applications (for example, in aerospace and medical systems) they are less familiar to developers of mainstream embedded systems. The work in this thesis began from the premise that – for a broad class of systems that have been implemented using an ET architecture – migration to a TT architecture would improve reliability. It may be tempting to assume that conversion between ET and TT designs will simply involve converting all event-handling software routines into periodic activities. However, the required changes to the software architecture are, in many cases rather more profound. The main contribution of the work presented in this thesis is to identify ways in which the significant effort involved in migrating between existing ET architectures and “equivalent” (and effective) TT architectures could be reduced. The research has taken an innovative step in this regard by introducing the use of ‘Design patterns’ for this purpose for the first time. This thesis describes the development, experimental testing and preliminary assessment of a novel set of design patterns. The thesis goes on to evaluate the effectiveness of some of the key patterns in the development of some representative systems. The pattern evaluation process involved both controlled laboratory experiments on real-time applications, and comprehensive feedback from experts in industry. The results presented in this thesis suggest that pattern-based approaches have the potential to simplify the migration process between ET and TT architectures. The thesis concludes by presenting suggestions for future work in this important area