Modelling and verification of embedded systems based on Petri net oriented representations

FACULTY OF ENGINEERING ELECTRONICS AND COMPUTER SCIENCE DEPARTMENT Doctor of Philosophy MODELLING AND VERIFICATION OF EMBEDDED SYSTEMS BASED ON PETRI NET ORIENTED REPRESENTATIONS by Mauricio Varea Driven by the demand for more functionality, the complexity involved in the design of embedded systems continues to increase. This has lead to a progressive increase in the amount of control and data flow that current embedded systems need to deal with. This dissertation addresses the interaction between these two domains and investigates its influence on the design of embedded systems, in terms of overall design cost. The first part of this dissertation presents the formalisation of a new design representation, called Dual Flow Net (DFN), which provides a tight control and data flow interaction. This is achieved by means of two new concepts. Firstly, the structure of the new DFN model is formulated employing a tripartite graph, as opposed to previous approaches based on a bipartite graph. Such a structure allows the use of a unique semantics to model the control flow, data flow, and its interactions. Secondly, a marking scheme that captures the changes in the state of the system produced by the separated effects of control and data flow is described. The analysis of behavioural properties using such a marking is proposed, and illustrative examples are given. The second part of this dissertation is concerned with the verification of DFN models through formal methods. A new set of algorithms for the symbolic model checking of DFN models is proposed. Behavioural properties of embedded systems, such as reachability, safety and liveness, are verified, using both Computation Tree Logic (CTL) and Linear Temporal Logic (LTL) formulae. The description of a new estimation method is provided, which is capable of allocating resources to the verification process efficiently, hence dealing with the state explosion problem. The algorithms and estimation method have been validated by examples of varying complexity, ranging from simple systems, in order to understand the modelling and verification principles, up to complex arrangements that depict real-life embedded systems, including an Ethernet coprocessor. The final part of this dissertation investigates the applicability of DFN models to the co-synthesis of hardware/software systems, as a potential application of the new design representation. It has been shown how the DFN model provides a flexible design framework for system-level trade-offs in the generated solution. ii