Determinate composition of FMUs for co-simulation

David Broman, Christopher Brooks, Lev Greenberg, Edward A. Lee, Michael Masin, Stavros Tripakis, Michael Wetter

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review


In this paper, we explain how to achieve deterministic execution of FMUs (Functional Mockup Units) under the FMI (Functional Mockup Interface) standard. In particular, we focus on co-simulation, where an FMU either contains its own internal simulation algorithm or serves as a gateway to a simulation tool. We give conditions on the design of FMUs and master algorithms (which orchestrate the execution of FMUs) to achieve deterministic co-simulation. We show that with the current version of the standard, these conditions demand capabilities from FMUs that are optional in the standard and rarely provided by an FMU in practice. When FMUs lacking these required capabilities are used to compose a model, many basic modeling capabilities become unachievable, including simple discrete-event simulation and variable-step-size numerical integration algorithms. We propose a small extension to the standard and a policy for designing FMUs that enables deterministic execution for a much broader class of models. The extension enables a master algorithm to query an FMU for the time of events that are expected in the future. We show that a model can be executed deterministically if all FMUs in the model are either memoryless or implement one of rollback or step-size prediction. We show further that such a model can contain at most one "legacy" FMU that is not memoryless and provides neither rollback nor step-size prediction.
Original languageEnglish
Title of host publicationProceedings of the Eleventh ACM International Conference on Embedded Software, EMSOFT '13
Number of pages12
ISBN (Print)9781479914432
Publication statusPublished - 2013
MoE publication typeA4 Article in a conference publication
EventInternational Conference on Embedded Software - Montreal, Canada
Duration: 29 Sep 20134 Oct 2013
Conference number: 13


ConferenceInternational Conference on Embedded Software
Abbreviated titleEMSOFT


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