Verification on Interrupt Timed Automata

The class of Interrupt Timed Automata (ITA) has been introduced to model multi-task systems with interruptions in a single processor environment. This is a subclass of hybrid automata in which real valued variables consist of a restricted type of stopwatches (variables with rate 0 or 1) organized along levels. While reachability is undecidable with usual stopwatches, it was proved that this problem is decidable in ITA and that untimed languages of ITA are effectively regular. Here we investigate the problem of model checking timed extensions of CTL over ITA and show in contrast that this problem is undecidable. On the other hand, we prove that model checking is decidable for two relevant fragments of this timed logic: (1) the first one where formula contain only model clocks and (2) the second one where formulas have a single external clock.