Passel : A Verification Tool for Parameterized Networks of Hybrid Automata

The Passel verification tool for parameterized networks of hybrid automata is presented in this paper. Passel automatically proves safety properties of networks of arbitrarily many interacting copies of a template hybrid automaton with rectangular dynamics by using a combination of invariant synthesis and inductive invariant proving. The invariant synthesis method generates quantified inductive invariants by transforming the set of reachable states of finite instantiations of the network. This is an extension to hybrid automata of the project-and-generalize method used in the invisible invariants method for synthesizing inductive invariants for parameterized networks of discrete automata. We use this extended method in a fixed-point iteration that is complete in the sense that it is ensured to generate an inductive invariants of a certain class of assertions for the parameterized network of hybrid automata. We present some of the engineering and design choices made in developing Passel, and present promising experimental results where the invariant synthesis procedure has been useful in automatically proving safety properties of examples like Fischer’s mutual exclusion protocol (with rectangular dynamics instead of clocks), a conceptual air-traffic control protocol, and others.