Specification of precise timing in synchronous dataflow models

Abstract

This paper proposes an extension to dataflow models with timing specifications to facilitate the construction of deterministic, platform independent, precisely timed models of software in cyber-physical systems (CPS). Dataflow models are often used to describe the software/cyber part of a CPS, owing to their succinct and analyzable representation of computation and concurrency. To capture the interaction of the cyber with the physical part, it is common practice to augment the dataflow model with nodes to represent physical sensors and actuators and handle the timing outside the dataflow model. However, the precise timing of these interactions is critical to the overall application behavior, and conventional dataflow models do not capture these timing requirements. In this work, we introduce timing configurations in dataflow models to specify when this communication between cyber and physical parts takes place. Timing specifications are derived from application requirements which are independent of the platform execution behavior. A correct implementation must fulfill the dataflow and timing requirements. This paper discusses the extension of the well-studied Synchronous Dataflow (SDF) model with timing configurations, shows how traditional SDF analysis for consistency and deadlock freedom is adapted for this model, and discusses hierarchical composition and analysis of composite SDF nodes with timing configurations. We believe that a model for the cyber part of a CPS must allow for the specification of application timing behavior as an integral part of the model. Timing extensions for dataflow models accomplish this in a natural and comprehensible manner. By illustrating timing configurations for SDF, we lay the groundwork for their application to a variety of dataflow models.