Monitoring and Fault-Diagnosis with Digital Clocks

International audienceWe study the monitoring and fault-diagnosis problems for dense-time real-time systems, where observers (monitors and diagnosers) have access to digital rather than analog clocks. Analog clocks are infinitely-precise, thus, not implementable. We show how, given a specification modeled as a timed automaton and a timed automaton model of the digital clock, a sound and optimal (i.e., as precise as possible) digital-clock monitor can be synthesized. We also show how, given plant and digital clock modeled as timed automata, we can check existence of a digital-clock diagnoser and, if one exists, how to synthesize it. Finally, we consider the problem of existence of digital-clock diag- nosers where the digital clock is unknown. We show that there are cases where a digital clock, no matter how precise, does not exist, even though the system is diagnosable with analog clocks. Finally, we provide a sufficient condition for digital-clock diagnosability. check whether the observed behavior satisfies the specification. This is the objective of the observer, which in this case is called a monitor. Our goal is to synthesize a monitor automatically from the specification. In the fault-diagnosis problem, we have a model of the system, for instance, in the form of an (untimed or timed) automaton. We also know that the system may produce some faults. However, these faults are not directly observable, thus, their occurrence must be deduced from other observations (this can be seen as a grey-box setting). The objective of the observer, which in this case is called a diagnoser, is to detect whether a fault occurred or not, and this as soon as possible after the fault happened. In this case, before we attempt to synthesize a diagnoser, we must first check existence of a diagnoser, called diagnosability. Indeed, a diagnoser may not exist in cases where the syste