Functional Mock-up Interface (FMI)

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The Functional Mock-up Interface (FMI) standard is an open and tool-independent standard for exchange of models between tools. FMI defines a C interface that is implemented by an executable called a Functional Mock-up Unit (FMU). A simulation environment, such as SystemModeler, can use the FMI to create an instance of the FMU and simulate it together with other FMUs or models native to the simulation environment.

The development of FMI was driven by an aspiration to create a standard in which a modeling environment could generate C code of a system model, which could then be utilized by other modeling and simulation environments, thereby making it easier to collaborate in modeling projects where different tools and workflows are used.

SystemModeler currently supports FMI 1.0 and 2.0 for Model Exchange (import and export) and FMI 2.0 for Co-Simulation (export only).

For a more detailed description of the FMU export and import workflow in SystemModeler, see the chapter on FMU Export and Import. The properties of the imported model are covered in Using an Imported FMU.

The Functional Mock-up Unit

An FMU, or a Functional Mock-up Unit, is the executable that implements the interface. During FMU export an FMU archive is generated from a systems model, while during FMU import a systems model is generated from an FMU archive.

An FMU contains the following:

Model Exchange and Co-Simulation

The FMI standards currently specify two types of protocols: FMI for Model Exchange (import and export), and FMI for Co-Simulation (master and slave). The main difference between these two protocols is that in Model Exchange the FMU is simulated using the importing tool's solver, while in Co-Simulation the FMU is shipped with its own solver.

FMI for Model Exchange allows FMUs to be used in offline or online simulation, where several FMUs can be connected together, or in embedded control systems on microprocessors. In both Model Exchange and Co-Simulation, the FMUs can potentially be very large, containing tens of thousands of variables.

For more general information about FMUs and the FMI standard, see www.fmi-standard.org.

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