A Hard Real Time Demo for Dynamic Ticks and Timed SCCharts

Abstract:
Synchronous programming languages, such as Esterel, Lustre, SCADE or SCCharts, have been developed for designing reactive systems. They abstract from computation times and assume that outputs are synchronous with their inputs. This leads to a deterministic semantics, without race conditions, which makes synchronous languages particularly suitable for safety-critical systems. However, even though synchronous languages have been designed with real-time applications in mind, the handling of physical time is traditionally left to the execution environment. This makes e.g. the expression of arbitrary time-outs difficult and may lead to excessive “busy waiting” computations. The recent proposal of dynamic ticks alleviates this by making physical time a first-class citizen within the synchronous programming model. In this paper, we explore and demonstrate the practical merits of dynamic ticks, including improved timing accuracy and reduced computational requirements, in the context of Timed SCCharts. As demonstration platform, we present a hardware/software platform that involves two stepper motors whose operation must be synchronized at microsecond accuracy to avoid physical damage.