Modelica Association: FMI¶

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Specifics¶

The Functional Mock-up Interface (FMI standard) is a standard for the exchange and simulation of Functional Mock-up Units (FMUs). With ecu.test FMUs can be tested and validated.

FMU simulation with ecu.test¶

For simulating FMUs, ecu.test uses the FMPy library. Both 64-bit and 32-bit FMUs are supported. To use 32-bit FMUs, a 64-bit wrapper is required, which can be added via the FMPy GUI.

Steps to integrate 32-bit FMUs:

1. Install FMPy and start the FMPy GUI.

2. Open the 32-bit FMU: File > Open

3. Add the 64-bit wrapper: Tool > Add Remoting > Windows 32-bit on Windows 64-bit

Simulation model configuration¶

As model file either an FMU (*.fmu) or a PythonFMU compatible Python file (*.py) can be used. For Python files ecu.test automatically generates a temporary PythonFMU when starting the configuration.

Access to signals and parameters¶

With ecu.test signals and parameters of an FMU can be read, written, and recorded. Stimulation of scalar test quantities is also possible.

The FMI standard distinguishes between continuous and discrete signals:

Discrete signals

Value changes occur only at solver event points.

Continuous signals

Values are kept current over the entire time span.

When stimulating FMU inputs, ecu.test processes value changes internally using a sampling frequency (communication step size). For discrete inputs external events (input events) are triggered so that value changes can be applied outside of solver events.

Simulation of multiple FMUs (Co-Simulation)¶

For simultaneous simulation of multiple FMUs a so-called Container FMU is required. The open-source project FMPy provides support for this:

• FMU container

• FMU container test

The Container FMU can be used like a regular FMU as model file.

FMU lifecycle¶

Procedure when working with FMUs:

1. Start configuration: FMU is unpacked to

   • Windows: %TEMP%/ecu.test_FMI/<Portname>

   • Linux: /tmp/ecu.test_FMI/<Portname>

   Alternatively the target directory can be adjusted using the environment variable ECUTEST_FMI_TEMPDIR so that the FMU is unpacked to %ECUTEST_FMI_TEMPDIR%/<Portname>.

2. Start simulation: Load the DLL (.so on Linux) via fmi2Instantiate.

3. Simulating: During the test case, model time in stepwise execution (see Temporal behaviour) is advanced by time-related test steps (e.g. Wait, or read/write with enabled Time Options).

4. Stop simulation: Unload the FMU via fmi2FreeInstance.

5. Stop configuration: Temporary files created for simulation are cleaned up.

Layered Standard for Network Communication (FMI-LS-BUS)¶

The Layered Standard for Network Communication extends the FMI 3.0 standard with the ability to simulate complex communication networks (e.g. CAN, LIN, FlexRay, CAN FD, CAN XL, Ethernet). FMI-LS-BUS defines a physical signal abstraction (High-Cut) and a network abstraction (Low-Cut) to enable detailed or simplified bus simulations. Via FMI-LS-BUS network signals can be defined as input and output variables of an FMU.

Configuration:

• For each terminal a separate Port BUSACCESS - CAN port must be added in the test bench configuration and the Bus terminal name must be configured. (Bus terminals are defined in the FMU’s terminalsAndIcons.xml.)

• The associated bus database must be specified either in the test bench configuration or in the Bus access tab of the test configuration.

After configuration start the available bus quantities are shown in the action window (Bus access tab).

Layered Standard for XCP (FMI-LS-XCP)¶

The Layered Standard for XCP extends the FMI 2.0 and 3.0 standard to include the ability to define the description and implementation of the XCP (Universal Measurement and Calibration Protocol) for FMUs. An FMU that supports XCP in accordance with FMI-LS-XCP allows access to internal measurement and calibration variables.

ecu.test enables access to measurement and calibration variables in FMUs that support FMI-LS-XCP.

Test bench configuration:

MODELACCESS-Port

Activate Automatic start/stop simulation

APPLICATION-Port

For Connection setup select At start of test execution

Priority

The MODELACCESS port must be started before the APPLICATION port and therefore have a lower Prio number. This ensures that the FMU is loaded first and the simulation is started before the APPLICATION port can access the XCP service, which is already running.

Test configuration:

A2L file

In the tab Control units, select the A2L file that was previously extracted from the FMU in a manual step.

A2L transport layer

Select XCP_ON_TCP_IP.

Properties 🛈¶