Coupling timed plant and controller models without introducing deadlocks

This paper focuses on timed models which represent closed-loop systems composed of a plant and a logic controller. Both plant and controller models are described in a formalism where urgent transitions are possible, to avoid non-realistic evolutions, and without deadlock when they are separated. It is first shown that deadlocks may occur in the plant model once the two models are coupled. To solve this issue, shared variables which model the changes of the inputs of the controller are defined and introduced in some actions of the plant model as well as in some guards of the controller model; the aim of these variables is to authorize evolutions of the controller only when at least one input has changed. This solution removes the previously pinpointed deadlocks and guarantees the reactivity of the controller.