OSP examples

This directory is a small collection of FMI and Open Simulation Platform (OSP) examples. It contains C++ FMU sources, a PythonFMU model, and an OSP system description that connects generated FMUs.

Directory map

osp-examples/
|-- .git/                    Git metadata for this examples checkout
|-- cpp-fmus/                C++ FMU project based on CPPFMU
|-- PythonFMU/               PythonFMU resistor model and build files
`-- system/                  OSP system structure and FMU files

cpp-fmus/

The C++ FMU project contains:

• CMakeLists.txt and cmake/ for configuring and packaging FMUs.
• src/ with the example FMU implementations.
• cppfmu/ with the CPPFMU framework submodule.
• fmi/ with FMI headers and support files.
• tools/ with utilities such as MergeFMUs.cmake.
• build.ps1 for the Windows build workflow.
• fail/, mock/, null/, and vector/ with example FMU sources.

Build it from this directory with CMake:

Set-Location cpp-fmus
git submodule update --init --recursive
cmake -S . -B build
cmake --build build

The generated FMUs are placed in the build/ directory. The project README also documents optional FMI compliance checks and merging platform-specific FMUs.

PythonFMU/

This directory contains a PythonFMU resistor example:

• demoslave.py defines the Resistor FMI 2.0 co-simulation slave.
• requirements.txt lists the model dependencies.
• build.ps1 contains the pythonfmu build command.

Build the example from this directory after installing PythonFMU:

Set-Location PythonFMU
pythonfmu build -f demoslave.py requirements.txt

PythonFMU host runtime

Important

When loading a PythonFMU in a non-Python host on Linux, set LD_PRELOAD to the full path of the shared library for the Python runtime that will execute the FMU before starting the host process. The library must match the Python version and architecture available on the target system; PythonFMU does not bundle Python.

For example, launch the host with:

LD_PRELOAD=/usr/lib/x86_64-linux-gnu/libpython3.11.so cosim run path/to/system

Replace the example path and version with the libpython library installed on your system. Setting LD_PRELOAD after the host has already started is too late. This Linux-specific step is needed for non-Python hosts; it is not required when the host process is Python itself.

On Windows, LD_PRELOAD does not exist. Instead, make the directory containing the matching Python DLL (python3.dll or a versioned DLL such as python311.dll) available on PATH before starting the non-Python host:

$env:PATH = "C:\Path\To\Python311;$env:PATH"
.\cosim.exe run path\to\system

Use a Python DLL with the same version and architecture as the environment that will execute the FMU. If the DLL is already discoverable by the host, no additional environment change is required.

system/

This is a runnable OSP system example:

• OspSystemStructure.xml selects fixed-step execution with a base step of 0.01 seconds.
• Resistor.fmu is the PythonFMU resistor model.
• vector.fmu supplies the voltage inputs and receives the resistor currents.

The connections in the system structure are:

vector.output[0]        -> resistor.positive_pin_v
vector.output[1]        -> resistor.negative_pin_v
resistor.positive_pin_i -> vector.input[0]
resistor.negative_pin_i -> vector.input[1]

Pass system/ to an OSP-compatible co-simulation runner to execute it and write simulation results.

Open simulation tools

Tool	Purpose	Link
libcosim	C++ co-simulation library and OSP execution engine.	GitHub repository
libcosim-cli / cosim	Command-line tool for running OSP/SSP simulations and inspecting FMUs. The upstream repository is named cosim-cli.	GitHub repository
libcosimpy	Python wrapper for libcosim through the C API.	GitHub repository
libcosimc	C API wrapping a subset of libcosim.	GitHub repository
cosim-demo-app	Server-client demo application demonstrating libcosim features.	GitHub repository
demo-cases	OSP co-simulation cases with OspSystemStructure.xml and SSP SystemStructure.ssd configurations.	GitHub repository
PythonFMU	Builds Python model code into FMI 2.0 co-simulation FMUs.	GitHub repository / PyPI package