Protocol Modelling Semantics for Embedded Systems

The properties of a domain oriented modelling approach or language are determined by the dominant semantics of the domain. A significant subclass that needs particular attention, because of its prevalence, is that of deterministic interactive embedded systems. Embedded systems contain both hardware and software components interacting with each other and with the users. The components should be modelled separately, and behaviour should be explicitly defined in order to ensure correct interaction between the components. In this paper we argue that a semantic framework known as protocol modelling provides a good basis for modelling interactive deterministic embedded systems. Firstly, we explain how protocol modelling represents interaction, and how it supports Hoare's CSP composition operator, thus allowing components of the solution to be modelled separately. Secondly, we show how protocol modelling can employ different modelling notations, focusing particularly on coloured Petri nets and state charts. Finally, we describe how it guarantees local reasoning about the trace behaviour of a composite based on consideration of the components. We illustrate these explanations using a simple mobile phone case study.