A model for a hard real time system executive

Abstract This paper presents a model of task activation in a real time software system. The model perceives such a system to be composed of a finite set of ‘reactions’, and provides a formal pattern for classification and specification of each single ‘reaction’. The model is complete in the sense that it covers all possible patterns of behaviour required of a task in a real time system. The paper proceeds to describe an executive - named RSEX - which implements the model. The ‘system calls’ to the executive are formulated according to the specification of a ‘reaction’, thus providing an ‘executable requirements’ language. The executive uses the ‘earliest deadline’ criterion for task scheduling, thus yielding an optimal implementation on a single processor system.