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Section: New Results

Fidelity in Real-Time Programming

Participants : Guillaume Baudart, Timothy Bourke.

In this work we study embedded systems with a significant mix of discrete reactive behaviours and `physical' timing constraints. The idea is to make the most of the advantages of synchronous languages for precisely specifying discrete behaviours but to adapt or extend them to treat real-time constraints more abstractly, that is, without an a priori definition of an eventual sampling interval.

This year we concluded our study of the Loosely Timed-Triggered Architectures (LTTA) by developing simplified models of the underlying implementations and protocols. This enabled us to improve the protocols, simplify the correctness and performance arguments, and compare them to systems built using modern clock synchronization algorithms. We developed our models in the Zélus programming language which enables (instances of) them to be compiled for simulation and contributes to our work on better exploiting synchronous languages for real-time specification and analysis. This work was presented at the EMSOFT conference and a journal article has been submitted.

This year we also concluded our study of the Quasi-synchronous Approach to modelling real-time distributed systems. We formalized the relation between the discrete abstraction proposed by Paul Caspi and the real-time archictectures for which it is intended. This enabled us to precisely state a correctness requirement for the abstraction and to show that it is sound for systems of two nodes (a typical case explored in other publications) but not for general systems of three or more nodes. Our formalization clarifies the relation between the causality of traces of the real-time system and the causality introduced by the synchronous abstraction. This enables us to state and show necessary and sufficient restrictions on the communication topologies and timing characteristics of systems to ensure soundness. A paper explaining this result has been drafted and will be submitted early in 2016.