Advanced Methodologies for Real-Time Discrete Event Modelling and Simulation

嵌入式实时系统是由与周围环境相互作用的组件组成的。这些都是高度反应性的系统，其中的决策可能导致对货物或生命的灾难性后果（工业自动化，运输，机器人等）。在这些系统中，不仅正确性很重要，执行系统任务的时机也很重要。建模和仿真已被证明是一种实用的方法来验证这些系统，降低成本和风险。正式的建模和仿真提供了更好的结果，因为可以更快、更安全地构建软件构件。特别是，离散事件系统规范形式化（DEVS）是一种基于通用动态系统概念的形式化建模和仿真框架，适合处理这些问题。***最近的研究主要集中在使用DEVS作为实时系统开发方法的框架。此外，通过在DEVS中建立严格的量子化系统理论，对DEVS理论进行了扩展。然而，用于实时系统的现有DEVS环境和形式都没有考虑RT应用中众所周知的问题，例如容错、传感器复制或瞬态系统过载。系统故障的发生通常会动态产生新的实时告警任务，使任务负荷超出系统的支持范围。已经提出了几种技术来解决这个问题。例如，不精确计算技术允许在瞬态过载下提供可控的退化（通过将任务划分为强制性部分以提供基本结果，可选部分以改进获得的结果；也可以提供相同任务的多个版本，根据当前负载使用不同的版本）。***我们的研究计划的目标是结合这些理论框架，提供一种基于DEVS的不精确实时计算技术。从方法论的角度来看，我们感兴趣的是开发一种使用不精确计算的动态实时DEVS理论。目标是提供安全性，减少开发时间，以及开发模拟的正式框架的优势。仿真结果可用于实时系统的开发。***从实际的角度来看，我们希望提供一套工具，可以应用于开发实时软件和模拟硬件在环（需要实时响应）。通过调用适当的执行引擎，我们将提供在逻辑时间（通常的仿真时钟）和实时时间（受限于挂钟时间）中执行模型的能力。这些工具可广泛应用于移动通信、应急规划或交通控制系统等领域。

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.