Formal specification of a reactive system: an exercise in VHDL, LOTOS and UNITY

Summary form only given. We are developing a specification and proof environment, called PREVAIL, which is to support several input languages (currently, only VHDL is supported) and which proposes a set of proof tools to verify appropriate descriptions/specifications. Nqthm is one of these tools, and we are working at defining an induction-based method to validate concurrent systems using this prover. To give such systems a formal specification, our first task was to choose between VHDL and one of the formal languages that can be of interest to hardware/software developers. Using a simple but significant reactive system as a running example, we give a comparative evaluation of VHDL and two formal languages: the ISO Formal Description Technique LOTOS, and the computational model UNITY. Thus we draw conclusions about the accuracy of each one of them with respect to different aspects (sequential behaviours, communications, non determinism, fairness, etc.).