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Reference FMUs

A set of hand-coded FMUs for development, testing and debugging of the Functional Mock-up Interface.

Use the fmusim executable to simulate an FMU:

> fmusim --help
Usage: fmusim [OPTION]... [FMU]
Simulate a Functional Mock-up Unit and write the output to result.csv.

  --help                           display this help and exit
  --interface-type [me|cs]         the interface type to use
  --tolerance [TOLERANCE]          relative tolerance
  --start-time [VALUE]             start time
  --stop-time [VALUE]              stop time
  --output-interval [VALUE]        set the output interval
  --start-value [name] [value]     set a start value
  --output-variable [name]         record a specific variable
  --input-file [FILE]              read input from a CSV file
  --output-file [FILE]             write output to a CSV file
  --log-fmi-calls                  log FMI calls
  --fmi-log-file [FILE]            set the FMI log file
  --solver [euler|cvode]           the solver to use
  --early-return-allowed           allow early return
  --event-mode-used                use event mode
  --record-intermediate-values     record outputs in intermediate update
  --initial-fmu-state-file [FILE]  file to read the serialized FMU state
  --final-fmu-state-file [FILE]    file to save the serialized FMU state


  fmusim BouncingBall.fmu  simulate with the default settings

You can download the pre-built Reference FMUs and fmusim executables from releases.

CSV file structure

fmusim uses CSV (comma separated values) files with the following structure as input and output format.

  • The file must be UTF-8 encoded.
  • The first line contains the names of the columns.
  • Each column name must match a variable name of the respective FMU.
  • Names that contain commas (,) must be surrounded by double quotes (").
  • The first column is the independent variable.
  • The values of the first column must be monotonically increasing.
  • Every line is terminated by a newline character (\n).
  • Every column is separated by a comma (,).
  • Every line must have the same number of columns.
  • The values must be stored in the same format as the start values of the respective variables in the modelDescription.xml.
  • String and Binary variables can only be scalars or arrays with only one element.
  • String values must be surrounded by double quotes (").


    <Float64 name="time" causality="independent"/>
    <Float64 name="Float64 array">
        <Dimension valueReference="2"/>
    <Boolean name="Boolean array">
        <Dimension valueReference="4"/>
    <Binary name="Binary scalar"/>
time,"Float64 array","Boolean array","Binary scalar"
0,1e-2 -1,0 false 1 true,666f6f
0.1,0.02 -2,1 false 0 true,aa6f6f
0.5,0.03 -3,1 true 0 false,66bb6f

Repository structure


  • config.h - model specific types and definitions
  • FMI{1CS|1ME|2|3}.xml - model descriptions
  • model.c - implementation of the model


  • fmi{|2|3}Functions.h - FMI header files
  • model.h - generic model interface
  • cosimulation.h - generic co-simulation interface


  • fmi{1|2|3}Functions.c - FMI implementations
  • cosimulation.c - generic co-simulation


  • *.c - various FMI 3.0 import examples
  • Examples.cmake - CMake configuration for the example projects


  • sources of the fmusim executable

Build the FMUs

To build the FMUs you need CMake and a supported build tool e.g. Visual Studio ≥ 2013 , Xcode or make:

  • download or clone the repository

  • open the CMakeGUI

  • click Browse Source... and select the cloned or downloaded and extracted repository (that contains CMakeLists.txt)

  • click Browse Build... and select the folder where you want build the FMUs

  • click Configure and select the generator for your IDE / build tool

  • select the FMI_VERSION you want to build and optionally the FMI_TYPE (only for FMI 1.0)

  • click Generate to generate the project files

  • click Open Project or open the project in your build tool

  • build the project

The FMUs will be in the dist folder inside the selected build folder.

Building fmusim

To build the fmusim executable, run the build/build_*.py <platform> Python scripts (where <platform> is the platform to build for, e.g. x86_64-windows) and enable WITH_FMUSIM before generating the CMake project.

License and attribution

Copyright © 2023, Modelica Association Project "FMI". All rights reserved. The code is released under the 2-Clause BSD License.

The Reference FMUs are a fork of the Test FMUs by Dassault Systèmes, which are a fork of the FMU SDK by QTronic, both released under the 2-Clause BSD License.