This report describes the usage and semantics of finite-state machines (FSMs) and modal models in Ptolemy II. FSMs are actors whose behavior is described using a finite set of states and transitions between the states. The transitions between the states are enabled by guards, which are boolean-valued expressions that can reference inputs to the actor and parameters in scope. The transitions can produce outputs and can update the value of parameters in scope. Modal models extend FSMs by allowing states to have refinements, which are hierarchical Ptolemy II models. The refinements may themselves be FSMs, modal models, or any composite actor containing a director compatible with the domain in which the modal model is being used. This report describes the operational semantics, the practical usage, and the semantics of time in modal models.
Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. Abstract This paper defines a suite of requirements for future hybrid cosimulation standards, and specifically provides guidance for development of a hybrid cosimulation version of the Functional Mockup Interface (FMI) standard. A cosimulation standard defines interfaces that enable diverse simulation tools to interoperate. Specifically, one tool defines a component that forms part of a simulation model in another tool. We focus on components with inputs and outputs that are functions of time, and specifically on inputs and outputs that are mixtures of discrete events and continuous time signals. This hybrid mixture is not well supported by existing cosimulation standards, and specifically not by FMI 2.0, for reasons that are explained in this paper. The paper defines a suite of test components, giving a mathematical model of an ideal behavior, plus a discussion of practical implementation considerations. The discussion includes acceptance criteria by which we can determine whether a standard supports definition of each component. In addition, the paper defines a set of test compositions of components. These compositions define requirements for coordination between components, including consistent handling of timed events.
The problem addressed by this paper is that real-time embedded software today is commonly built using programming abstractions with little or no temporal semantics. The focus is on computer-based systems where multiple computers are connected on a network and interact with and through physical processes (the plant) via sensors and actuators. Such systems are often termed cyber-physical systems (CPS).The paper discusses the use of an extension to the Ptolemy II framework as a coordination language for the design of distributed real-time embedded systems. Specifically, the paper shows how to use modal models in the context of the PTIDES extension of Ptolemy II to provide a firm basis for the design of an important class of problems. Several examples are given to show the use of this environment in the design of interesting practical real-time systems.
This paper discusses the use of the Ptides model of computation as a coordination language for the design of deterministic, event-driven, real-time, distributed embedded systems. Specifically, the paper shows how the use of synchronized clocks in the context of Ptides enables explicit, platform independent specification of functionality and timing. From this specification, we generate code for two target platforms: Renesas and XMOS. The generated code includes a lightweight operating system which performs scheduling, I/O and network handling as well as application specific tasks.Ptides models are developed in Ptolemy, a design and simulation environment for heterogeneous systems. This framework also contains a code generation framework which is leveraged to derive Ptides implementations from the models. We illustrate our approach by designing a simple Ptides application, a small component in a printing press responsible for on-the-fly changeover between paper rolls. We demonstrate the design process and show that the generated code exhibits identical timing at the cyber-physical boundary on multiple implementation platforms.
We consider certain spaces of linear signals equipped with a standard prefix relation and a suitably defined generalized distance function. We introduce a new class of abstract structures, which we call generalized ultrametric semilattices, and prove a representation theorem stating that every generalized ultrametric semilattice with a totally ordered distance set is isomorphic to a space of that kind. It follows that the formal definition of generalized ultrametric semilattices with totally ordered distance sets constitutes an axiomatization of the first-order theory of those spaces.
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