Advanced Methodologies for Real-Time Discrete Event Modelling and Simulation

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Embedded real-time systems are built as sets of components interacting with their surrounding environment. These are highly reactive systems, where the decisions can lead to catastrophic consequences for goods or lives (industrial automation, transport, robotics, etc.). In these systems, not only correctness is critical, but also the timing for executing the system tasks. Modeling and Simulation has proven to be a practical approach to verification of these systems with reduced costs and risks. Formal modeling and simulation provides even better results as the software artifacts can be built faster and safer. In particular, the Discrete-EVent Systems specification formalism (DEVS), a formal modeling and simulation framework based on generic dynamic systems concepts, is suitable to deal with these issues. ***Recent research has been oriented in using DEVS as a framework for Real-time systems development method. In addition, DEVS theory has been extended by formulating a rigorous theory of quantized systems in DEVS. Nevertheless, none of the existing DEVS environments and formalisms used for real-time systems has considered well-known problems in RT applications, for instance, fault tolerance, sensor replication or transient system overloading. The occurrences of system failures usually generate new real-time alarm tasks dynamically, generating a task load that cannot be supported by the system. Several techniques have been proposed to solve this problem. For instance, the techniques of imprecise computation allow to provide controlled degradation under transient overloads (by dividing the tasks in a mandatory part to provide basic results, and an optional part to improve the results obtained; also multiple versions of the same task can be provided, using a different version depending on the present load). ***The goal of our research program is to combine these theoretical frameworks, providing a technique for imprecise real-time computing based on DEVS. From the methodological point of view, we are interested in developing a theory of dynamic real-time DEVS using imprecise computing. The goal is to provide security, reduction in the development times, and the advantages of a formal framework to develop simulations. The results of the simulated system can be applied in the development in the real-time system. ***From the practical point of view, we expect to provide a set of tools that can be applied to develop real-time software and simulations with hardware-in-the-loop (requiring real-time response). By invoking appropriate execution engines, we will provide the ability to execute models in both logical time (the usual simulation clock) and real time (constrained to wall-clock time). These tools can be applied to a wide range of applications, ranging from mobile communication, emergency planning or traffic control systems.