TOML configuration

Keep reusable settings in source TOML overlays and generate a complete TOML for each run. The generated file records the firmware, tools, model, parameters, and helper commands. The generator resolves tool locations and replaces legacy ${NAME:-default} expressions with their literal defaults.

For reusable changes, write a small overlay, for example my-copter.toml:

[FMU.models.quadrotor.parameters]
mass = 2.7

[Run.processes.mission]
enabled = false

Then generate the complete configuration:

fastdyn-config --base configs/copter462.toml \
  --overlay my-copter.toml --output out/my-copter.toml

Overlays merge tables recursively; an array or scalar replaces the previous value. Repeat --overlay to apply files in order. Model parameters in an overlay are merged with the base parameters, so explicitly override every physical quantity that changes with the vehicle.

Tools and model selection

[FMU]
compiler = "rumoca"
active = "quadrotor"
auto_build = true

[FMU.models.quadrotor]
model = "FastDyn.Copter"
model_file = "modelica/FastDyn/Copter.mo"
source_roots = ["modelica", "third_party/common/modelica_models"]
output = "out/fmi3/Copter"
build = true
release = false

[FMU.models.quadrotor.parameters]
mass = 2.5644001
arm_length = 0.25

compiler can be a name on PATH or the executable path generated by Nix. Without it, FastDyn runs Cargo in the pinned Rumoca submodule. release selects Cargo’s build profile and has no effect on a prebuilt compiler.

auto_build checks whether the FMU is absent or older than the Modelica source files. After changing the compiler revision, explicitly rebuild with utils/build_fmi3_fmu.py; the timestamp check does not detect compiler changes. Numeric scalars and rectangular arrays are passed during FMI initialization. Unknown names and incompatible dimensions are rejected. A compiler can fold derived expressions into constants: when changing physical properties, prefer a Modelica variant and rebuild, then verify the values evaluated by the FMU. The payload study compiles every variant for this reason.

Vehicle parameters

For FastDyn.Copter, mass is in kg and inertia[3,3] is the body inertia tensor in kg m². For a diagonal tensor, a TOML override is:

[FMU.models.quadrotor.parameters]
inertia = [[0.02601237985, 0.0, 0.0], [0.0, 0.02590943825, 0.0], [0.0, 0.0, 0.045571756801]]

An override must refer to an independent FMI parameter. A Modelica parameter bound to another parameter can be exported as calculatedParameter; FastDyn rejects writing it before launching the firmware. Set the independent source parameter instead, or change the Modelica binding and rebuild. The payload’s attachment_b uses explicit motor coordinates so all three components remain editable from TOML. Use the parameter names exposed by the model you are compiling. arm_length is the center-to-motor distance, so the motor diagonal is twice that number. Thrust is Ct * omega²; Cm is the rotor torque-to-thrust ratio in meters. PWM spans pwm_min to pwm_max, mapped to omega_min through omega_max in rad/s. tau_up and tau_down set the motor response times in seconds.

lat0, lon0, and ground_alt_wgs84 define the geodetic origin. If you move it, update the mission waypoint coordinates too. The model source files list the parameters for Plane and Rover.

Firmware and helpers

[[CPU.cpu0]] selects the firmware binary, plugin library, and existing peripheral configuration. [Machine] selects QEMU, the board, and timing. The supplied ArduPilot examples use a 1 ms timer IRQ; keep that setting for these firmware builds.

[Run.processes.mavproxy] records telemetry and starts the viewer. [Run.processes.mission].command supplies the MAVLink endpoint, ArduPilot parameter file, and QGC WPL waypoint file. Edit those literal arguments in TOML to select another mission or tune. ArduPilot’s native parameter file is separate from the plant’s TOML parameters: controller gains change firmware behavior, while mass and inertia change the simulated vehicle.

Set a helper’s enabled = false to disable it. Use terminate_run_on_exit = true for a mission that should end the simulation when it completes. [Rumoca].enabled controls a separate optional Rumoca process; it is false for the FMI-in-QEMU examples.

The repository’s docs/Configuration.md provides the broader peripheral and device-model reference.