Schedulability analysis of distributed cyber-physical applications on mixed time-/event-triggered bus architectures with retransmissions

Abstract

In this paper we study the setup where multiple cyber-physical applications are partitioned and mapped onto spatially distributed electronic control units (ECUs). Further, applications communicate over a mixed time-/event-triggered bus like FlexRay. Such a setting commonly arises in automotive and other distributed cyber-physical systems. All control messages mapped onto the time-triggered or static segment of the bus result in negligible/zero communication delays (viz., the bus and the ECUs can be perfectly synchronized) and hence good control performance. At the other extreme, all messages scheduled in the priority-driven dynamic segment often result in poor control performance because of the intrinsic timing non-determinism of priority-based protocols. In this paper we are concerned with the intermediate case — where messages are dynamically moved between the time- and event-triggered segments in order to meet performance requirements in the presence of disturbances — and formally study the schedulability analysis problem on the bus. In particular, we propose a novel scheduling strategy that considerably reduces the number of static time-triggered slots required in such a switching scheme to meet specified performance requirements. The basic premise of our work is that time-triggered slots are expensive and, hence, they should be used sparingly. We further demonstrate the benefits of our proposed scheme through a number of illustrative examples.