FMU4cpp

FMU4cpp is a GitHub template repository that allows you to easily create cross-platform FMUs compatible with FMI 2.0 & FMI 3.0 for Co-simulation using CMake and C++.

The framework generates the required modelDescription.xml and further packages the necessary content into a ready-to-use FMU archive.

How do I get started?

1. Clone this repository using the "Use this template" button.
2. Browse the example models from the examples branch.
3. Implement your own model by inheriting from the provided fmu_base abstract class.
4. Create an FMU target by using the provided generate_fmu CMake function.
5. Build. Models for your platform are located in a models folder within the build folder.
6. Upload your changes to GitHub to trigger cross-compilation and validation against fmusim.
7. Download cross-compiled FMUs from the Actions tab.

Alternate workflow using CMake FetchContent

You can also use FMU4cpp as a CMake FetchContent dependency in a pre-existing CMake project.

include(FetchContent)
FetchContent_Declare(
    fmu4cpp
    GIT_REPOSITORY https://github.com/Ecos-platform/fmu4cpp.git
    GIT_TAG git_tag_commit_or_branch_to_use
)
FetchContent_MakeAvailable(fmu4cpp)

Then, you can create your own FMU by inheriting from fmu4cpp::fmu_base and using the generate_fmu function.

Example (BouncingBall)

#include <fmu4cpp/fmu_base.hpp>

using namespace fmu4cpp;


class BouncingBall : public fmu_base {

public:
    FMU4CPP_CTOR(BouncingBall) {

        register_real(
                "height", &height)
                .setCausality(causality_t::OUTPUT)
                .setVariability(variability_t::CONTINUOUS))
                .setInitial(initial_t::EXACT);

        register_real(
                "velocity", &velocity)
                .setCausality(causality_t::LOCAL)
                .setVariability(variability_t::CONTINUOUS);

        register_real(
                "gravity", &gravity)
                .setCausality(causality_t::PARAMETER)
                .setVariability(variability_t::FIXED);

        register_real(
                "bounceFactor", &bounceFactor)
                .setCausality(causality_t::PARAMETER)
                .setVariability(variability_t::FIXED);


        BouncingBall::reset();
    }

    bool do_step(double dt) override {
        // Update velocity with gravity
        velocity += gravity * dt;
        // Update height with current velocity
        height += velocity * dt;

        // Check for bounce
        if (height <= 0.0f) {
            height = 0.0f;                      // Reset height to ground level
            velocity = -velocity * bounceFactor;// Reverse velocity and apply bounce factor
        }

        return true;
    }

    void reset() override {
        height = 10;
        velocity = 0;
        gravity = -9.81f;
        bounceFactor = 0.6f;
    }

private:
    double height{};      // Current height of the ball
    double velocity{};    // Current velocity of the ball
    double gravity{};     // Acceleration due to gravity
    double bounceFactor{};// Factor to reduce velocity on bounce
};

model_info fmu4cpp::get_model_info() {
    model_info info;
    info.modelName = "BouncingBall";
    info.description = "A bouncing ball model";
    return info;
}

FMU4CPP_INSTANTIATE(BouncingBall);

Cross-compilation

Cross-compilation (64-bit linux/windows) occurs automatically when you push your changes to GitHub.

Such easy, such wow.

Requirements

• C++17 compiler
• CMake >= 3.15