Marten Lohstroh

FIDE: an FMI integrated development environment

This paper presents FIDE, an Integrated Development Environment (IDE) for building applications using Functional Mock-up Units (FMUs) that implement the standardized Functional Mock-up Interface (FMI). FIDE is based on the actororiented Ptolemy II framework and leverages its graphical user interface, simulation engine, and code generation feature to let a user arrange a collection of FMUs and compile them into a portable and embeddable executable that efficiently co-simulates the ensemble. The FMUs are orchestrated by a well-vetted implementation of a master algorithm (MA) that deterministically combines discrete and continuous-time dynamics. The ability to handle these interactions correctly hinges on the implementation of extensions to the FMI 2.0 standard. We explain the extensions, outline the architecture of FIDE, and show its use on a particularly challenging example that cannot be handled without the proposed extensions to FMI 2.0 for co-simulation.

Hybrid co-simulation: it’s about time

Model-based design methodologies are commonly used in industry for the development of complex cyber-physical systems (CPSs). There are many different languages, tools, and formalisms for model-based design, each with its strengths and weaknesses. Instead of accepting some weaknesses of a particular tool, an alternative is to embrace heterogeneity, and to develop tool integration platforms and protocols to leverage the strengths from different environments. A fairly recent attempt in this direction is the functional mock-up interface (FMI) standard that includes support for co-simulation. Although this standard has reached acceptance in industry, it provides only limited support for simulating systems that mix continuous and discrete behavior, which are typical of CPS. This paper identifies the representation of time as a key problem, because the FMI representation does not support well the discrete events that typically occur at the cyber-physical boundary. We analyze alternatives for representing time in hybrid co-simulation and conclude that a superdense model of time using integers only solves many of these problems. We show how an execution engine can pick an adequate time resolution, and how disparities between time representations internal to co-simulated components and the resulting effects of time quantization can be managed. We propose a concrete extension to the FMI standard for supporting hybrid co-simulation that includes integer time, automatic choice of time resolution, and the use of absent signals. We explain how these extensions can be implemented modularly within the frameworks of existing simulation environments.

An Interface Theory for the Internet of Things

This paper uses interface automata to develop an interface theory for a component architecture for Internet of Things (IoT) applications. Specifically, it examines an architecture for IoT applications where so-called “accessors” provide an actor-oriented proxy for devices (“things”) and services. Following the principles of actor models, an accessor reacts to input stimuli and produces outputs that can stimulate reactions in other accessors or actors. The paper focuses on a specialized form of actor models where inputs and outputs to accessors and actors are time-stamped events, enabling timing-sensitive IoT applications. The interaction between accessors and actors via time-stamped events forms a “horizontal contract,” formalized in this paper as an interface automaton. The interaction between an accessor and the thing or service for which it is a proxy is a “vertical contract,” also formalized as an interface automaton. Following common practice in network programming, our vertical contract uses an asynchronous atomic callback (AAC) pattern. The formal composition of these interface automata allows us to reason about the combination of a timed actor model and the AAC pattern, enabling careful evaluation of design choices for IoT systems.

Step revision in hybrid Co-simulation with FMI

This paper presents a master algorithm for co-simulation of hybrid systems using the Functional Mock-up Interface (FMI) standard. Our algorithm introduces step revision to achieve an accurate and precise handling of mixtures of continuous-time and discrete-event signals, particularly in the situation where components are unable to accurately extrapolate their input. Step revision provides an efficient means to respect the error bounds of numerical approximation algorithms that operate inside co-simulated FMUs. We first explain the most fundamental issues associated with hybrid co-simulation and analyze them in the framework of FMI. We demonstrate the necessity for step revision to address some of these issues and formally describe a master algorithm that supports it. Finally, we present experimental results obtained through our reference implementation that is part of our publicly available open-source toolchain called FIDE.

Hybrid Co-simulation: It's About Time

Model-based design methodologies are commonly used in industry for the development of cyber-physical systems (CPSs). There are many different languages, tools, and formalisms for model-based design ...

Contextual callbacks for resource discovery and trust negotiation on the internet of things: work-in-progress

This paper introduces contextual callbacks, which allow environments to authenticate themselves to nearby devices and advertise local services in response to the reception of radio-broadcast announcements that are emitted by mobile devices.

Demo Abstract: Building IoT Applications with Accessors in CapeCode

We demonstrate CapeCode, a tool for composing actor-oriented building blocks for applications in the Internet of Things design space.