Illegal call sequence

[AnHeuermann]

Description

I think I'm using FMI.jl to call FMI2 functions in an illegal call sequence.
When the FMU is in event mode it should not be allowed to call fmi2SetReal on a non-input variable.

I'm not sure if I want this to get fixed, because I'm doing it wrong by changing a non-input variable that is not a state
and need this capability of FMI.jl.

How to reproduce

Create a FMI 2 ModelExchange FMU with e.g. OpenModelica for

model simpleLoop
  Real r(min = 0);
  Real s(min = -sqrt(2), max = sqrt(2));
  Real x(start=1.0), y(start=0.5);
  Real x_ref, y_ref;
equation
  r = 1+time;
  s = sqrt((2-time)*0.9);

  r^2 = x^2 + y^2;
  r*s = x + y;

  x_ref = r * (s/2 + sqrt(1/2-s^2/4));
  y_ref = r*s - x_ref;
end simpleLoop;

Here variables r and s should have default variability continuous and causality local:

<ScalarVariable
  name="r"
  valueReference="0"
  >
  <Real min="0.0"/>
</ScalarVariable>
<ScalarVariable
  name="s"
  valueReference="1"
  >
  <Real min="-1.414213562373095" max="1.414213562373095"/>
</ScalarVariable>

Judging from the State Machine of Calling Sequence (FMI Specification 2.0.2 section 3.2.3) it is only allowed to call fmi2SetReal on a real input variables.
So if it has causality=input and variability=continuous
or it has causality=input and variability=discrete
or variability=tunable.

As far as I can tell FMI.jl is not stopping me from calling fmiSet on r or s.

import FMI
import FMIImport
fmu = FMI.fmiLoad("simpleLoop.fmu")
FMI.fmiInstantiate!(fmu)
# FMU instantiated
FMI.fmiSetupExperiment(fmu, 0.0, 1.0)
FMI.fmiEnterInitializationMode(fmu)
# FMU in initialization iode
FMI.fmiExitInitializationMode(fmu)
# FMU in event mode
FMIImport.fmi2SetReal(fmu, "r", 42)  # Illegal call

Expected Result

Throw an error when calling fmi2SetReal is not allowed and add a flag to allow illegal call sequences anyway.

Versions 'n Stuff

• Julia: Julia Version 1.8.1
• OS: Ubuntu Focal
• FMI.jl v0.10.0
• FMIImport.jl v0.11.1

[ThummeTo]

Jap, we can check for that.
However most FMUs return warnings/errors if calling sequence is violated - in some cases variables are settable without issues (and applied) even if it's against the calling sequence (e.g. because the properties defined in the model description aren't 100% correct), so we should not prevent the user from doing so if the FMU can handle it. Warning seems a nice in-between.