Process Control Design Using SPIN

This paper reports an experience with the modeling, verification and concurrent implementation of a medium-sized process control problem. The case study was proposed by Forschungszentrum Informatik, Karlsruhe in 1993 in order to promote the usage of formal methods in industry. It concerns an industrial robotics application that processes metal plates. A top-down design approach is followed where successive CCS and Promela specification levels of decreasing abstraction are considered, each layer little by little allows verification of parts of the security requirements thus providing a mean for coping with state explosion. The level refinements are checked with the Concurrency Workbench a CCS-based tool. Safety and liveness requirements are expressed in linear temporal logic and checked with SPIN. From the ultimate specification, two different implementations are derived. The first one is in Synchronous C++, a concurrent extension of C++ and the second in Regis/Darwin. This application shows that SPIN is also quite appropriate for developing control process problem from scratch and with requirements to be checked in mind. It appeared clearly that the specification phase was very important for obtaining a satisfactory specification from which a well behaved implementation was derived easily in a few days.