From CRSM to a Tasking Design

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.