Section: New Results

Quasi-synchrony

Participants : Guillaume Baudart, Timothy Bourke, Marc Pouzet.

We study the implementation of critical control applications on the so-called quasi-periodic distributed architectures. These architectures, used in civil avionics (e.g., Airbus A380), consist of a collection of distributed processors running with quasi-periodic clocks, that is, un-synchronized physical clocks subject to bounded jitterring. The theory of quasi-synchrony has been introduced by Paul Caspi in the 2000'  [29] . Loosely Time-Triggered Architectures (LTTA) denotes such architectures with the prototocol used to implement a synchronous program on top of it.

Over the last ten year two protocols were considered: (1) Back-Pressure LTTA  [25] based on a acknowledgement mechanism reminiscent of elastic circuit  [43] . (2) Time-Based LTTA  [28] which uses timing constraints of the architecture to mimic a synchronous execution.

During year 2014, we have entirelly reformulated the model of LTTA using synchronous semantics and principles. Compared to previous formalizations based on Petri nets  [24] , this new presentation is is simpler and more uniform with the same theoretical model used for both the application and the protocol ((1) or (2)). Moreover, it is easier to consider mixed protocols (a whole application with part based on time-based communication and others based on back-pressure). Besides this, we also proposed a new and more flexible Time-Based LTTA, allowing for pipelining by not reconstructing global synchronization, unlike what was done in previous Time-Based LTTA.