From CRSM to a Tasking Design

Abstract

This paper introduces elements to facilitate crossing of the gap between analysis and design in the case of real-time applications relying on multitasking operating system. The chosen specification method is based on the use of Shaw’s CRSM (Communicating Real-Time States Machines) and our purpose is to put the basis of a method for an easier translation of a CRSM-based modelling of a system into a real-time multitasking execution model. In order to do this, we present guidelines for translating the basic constructs of a CRSM model (communicating machines, channels, transitions) into programs involving the usual objects and primitives found in off-the shelf real-time multitasking operating systems (tasks or threads, message passing, event signalling ...). The guidelines are illustrated with the classical specification example of the Martian Lander. The aim is to overcome the gap between a specification made with the CRSM and a multitasking execution model: this will then enable good possibilities for verification. The specification can be executed and the design can be verified for correctness (liveliness, safety). Eventually, a comparison between the behaviour of the specified model and that of the target program can be made.