Real Time Behavior of Data in Distributed Embedded Systems

Abstract

Nowadays, embedded systems appear more and more as distributed systems structured as a set of communicating components. Therefore, they show a less deterministic global behavior than centralized systems and their design and analysis must address both computation and communication scheduling in more complex configurations. We propose a modeling framework centered on data. More precisely, the interactions between the data located in components are expressed in terms of a so-called observation relation. This abstraction is a relation between the values taken by two variables, a source and an image, where the image gets past values of the source. We extend this abstraction with time constraints in order to specify and analyze the availability of timely sound values.

The formal description of the observation-based computation model is stated using the formalism of transition systems, where real time is handled as a dedicated variable. As a first result, this approach allows to focus on specifying time constraints attached to data and to postpone task and communication scheduling matters. At this level of abstraction, the designer has to specify time properties about the timeline of data such as their freshness, stability, latency… As a second result, a verification of the global consistency of the specified system can be automatically performed. The verification process can start either from the timed properties (e.g. the period) of data inputs or from the timed requirements of data outputs (e.g. the latency). Lastly, communication protocols and task scheduling strategies can be derived as a refinement towards an actual implementation.