The Tool KRONOS

KRONOS [6, 8] is a tool developed with the aim to assist the user to validate complex real-time systems. The tool checks whether a real-tinae system modeled by a t imed automaton [4] satisfies a timing property specified by a formula of the temporal logic TCTL [3]. KRONOS implements the symbolic model-checking algorithm presented in [11], where set of states are symbolically represented by linear constraints over the clocks of the timed automaton. In this work we present two other verification approaches we have recently implemented in KRONOS, namely forward analysis and minimization, that rely on the same symbolic representation of the state space. The emphasis is given in illustrating the interest of the two approaches rather than thoroughly presenting their technical details which can be found in [15, 7]. Forward analysis is based on the symbolic simulation of a timed automaton. By computing the set of all possible runs, starting from some given set of initial states, we can veri~" some interesting temporal properties on the behavior of the system, such as reachabilily, invariance and bou~ded response. This method turns to be in many cases more efficient than model-checking and it has the advantage that it allows error diagnosis. Minimization consists in constructing the smallest finite quotient of the timed model with respect, to a bisimulation equivalence. This method allows using timed au tomata not only for describing the behavior of the system but also for speci~'ing the requirements. We can then check whether the minimal model of the system simulates or is equivalent to the one of the specification. The paper is organized as follows. In section 2 we review timed automata. In section 3 we present the basis of symbolic forwardanalysis and the algorithms implemented in KROXOS. and in section 4 we apply this method for verifying the FDDI protocol [12]. In section 5 we present the minimization algorithm and in section 6 we analyze the Fischer's mutual exclusion protocol [1].