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Functional Mock-up Interface

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The Functional Mock-up Interface (or FMI) defines a standardized interface to be used in computer simulations to develop complex cyberphysical systems.

Functional Mock-up Interface
AbbreviationFMI
StatusPublished
Year started2010
Latest version1.0
OrganizationMODELISAR
DomainComputer simulation
LicenseCC_BY_SA 3.0
WebsiteFMI website

The vision of FMI is to support this approach: if the real products is to be assembled from a wide range of parts interacting together in complex ways that each is controlled by a complex set of physical laws , then it should be possible to create a virtual product that can be assembled from a set of models that each represent a combination of parts, interacting using each a model of the physical laws as well as a model of the control systems (using electronics, hydraulics, digital software, ..) assembled digitally. FMI thus provide the means for model based development of systems, and is used for example for designing functions that are driven by electronic devices inside vehicles (eg. ESP controller, active safety systems, combustion controller). Activities from systems modeling, simulation, validation and test can be covered with the FMI based approach.

To create FMI, a large number of software companies and research centers have worked in a cooperation project established through a European consortium that is conducted by Dassault Systèmes under the name of MODELISAR. The MODELISAR project has been initialized in 2008 to define the FMI specifications, deliver technology studies, and prove the FMI concepts through Use Cases elaborated by the consortium partners.

The development of the FMI specifications was coordinated by Daimler AG.

The FMI specifications are distributed under open source licence.

The four required FMI aspects of creating models capable of being assembled have been covered in in Modelisar project:

  • FMI for Model Exchange,
  • FMI for Co Simulation,
  • FMI for Applications,
  • FMI for PLM (integration of models and related data in the Product Life Cycle Management).


[1]

FMI has two objectives[2]:

  • A modeling environment can export a model composed of C (programming language) code packaged with an XML definition documenting the model. This XML definition is for a model is called FMU (Functional Mock-up Unit)
  • Several models can communicate at runtime in a co-simulation environment by using the definitions of their interfaces.

Architecture

Each FMU (Functional Mock-up Unit) model is distributed in zip files with the extension ".fmu" which contains[1]:

  • An XML file containing among other things the definition of the variables used by the FMU.
  • All the equations used by the model (defined as a set of C functions).
  • optional other data, such as parameter tables, User Interface, documentation which may be needed by the model.

Example

below is an example of an FMI model description issued from Modelica. 

<?xml version="1.0" encoding="UTF8"?>
<fmiModelDescription
  fmiVersion="1.0"
  modelName="ModelicaExample"
  modelIdentifier="ModelicaExample_Friction"
...
  <UnitDefinitions>
     <BaseUnit unit="rad">
        <DisplayUnitDefinition displayUnit="deg" gain="23.26"/>
     </BaseUnit>
  </UnitDefinitions>
  <TypeDefinitions>
     <Type name="Modelica.SIunits.AngularVelocity">
        <RealType quantity="AngularVelocity" unit="rad/s"/>
     </Type>
  </TypeDefinitions>
  <ModelVariables>
     <ScalarVariable
        name="inertia1.J"
        valueReference="16777217"
        description="Moment of inertia"
        variability="parameter">
        <Real declaredType="Modelica.SIunits.Torque" start="1"/>
     </ScalarVariable>
...
  </ModelVariables>
</fmiModelDescription>

FMI proponents explain that FMI models have several advantages over Simulink S-Functions[3]:

  • S-Functions format is proprietary, whereas the FMI schema is licensed under a BSD license,
  • The building blocks of S-Functions are much more complex than FMI, making it very difficult to integrate in other simulators than Simulink itself. Furthermore, the S-Functions format is specific to Simulink.
  • S-Functions are not suited for embedded systems, due to the memory overhead of S-Functions

Support

As of January 2011, FMI is supported on the following simulation frameworks[1]:

See also

References

  1. ^ a b c "Functional Mockup Interface (FMI)". modelica.org. January 2010. Retrieved 2011-012-22. On Jan. 26, version 1.0 of the open Functional Mockup Interface was released (FMI for model exchange 1.0). This interface was developed in the ITEA2 MODELISAR project to support the model exchange between modelling and simulation tools. The Modelisar project is coordinated by Dassault Systèmes. The FMI development has been organized by Daimler. {{cite web}}: Check date values in: |accessdate= (help)
  2. ^ "FMI". modelisar.org. Retrieved 2011-01-22.
  3. ^ Martin Otter, Hilding Elmqvist, Torsten Blochwitz, Jakob Mauss, Andreas Junghanns, Hans Olsson. "Functional Mockup Interface – Overview" (PDF). http://synchronics.inria.fr (INRIA). Retrieved 2011-01-23. {{cite web}}: External link in |publisher= (help)CS1 maint: multiple names: authors list (link)
 

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