Real-Time Signaling in SDL

SDL is a formal specification language for distributed systems, which provides significant, yet limited real-time expressiveness by its notion of time (now) and its timer mechanism. In our current work, we are investigating various ways to augment this expressiveness, by proposing language extensions and exploiting degrees of freedom offered by SDL’s formal semantics. This paper presents some recent results of our work: a mechanism for real-time signaling, which can be roughly characterized as a generalization of SDL timers. More specifically, we propose to add the possibility of specifying a time interval for the reception of ordinary SDL signals, by stating their time of arrival and expiry. This extension can be used, for instance, to specify time-triggered scheduling, which is required in many real-time systems. In the paper, we present the concept of real-time signaling, propose a syntactical extension of SDL, define its formal semantics, outline our implementation, show excerpts of a control application, and report on measurement results.