The effective use of model-based formal methods in the development of complex embedded systems requires the integration of discrete-event models of controllers with continuous-time models of their environments. This paper proposes a new approach to the development of such combined models (co-models), in which an initial discrete-event model may include approximations of continuous-time behaviour that can subsequently be replaced by couplings to continuous-time models. An operational semantics of co-simulation allows the discrete and continuous models to run on their respective simulators and managed by a coordinating co-simulation engine. This permits the exploration of the composite co-model's behaviour in a range of operational scenarios. The approach has been realised using the Vienna Development Method (VDM) as the discrete-event formalism, and 20-sim as the continuous-time framework, and has been applied successfully to a case study based on the distributed controller for a personal transporter device.

We show that timed automata can be used to model and to analyze timeliness properties of embedded system architectures. Using a case study inspired by industrial practice, we present in detail how a suitable timed automata model is composed. Exact upper bounds on the timeliness properties can be found with the Uppaal model checker for a number of usage scenarios. We compare our results with three other performance modeling techniques. This comparison shows that if the state space of the model is tractable, Uppaal gives the most accurate results at similar cost. The proposed modeling strategy can be automated, which alleviates the difficulty and error-proneness of manually constructing timed automata models