Add simulation parameter for setting default clock period

[Bernhard Thiele]

The MLS mentions a default clock at page 195:

A default clock, if neither a Real interval, nor a Rational interval nor a Boolean clock is associated with a base partition. In this case the default clock is associated with the fastest sub-clock partition. [Typically, a tool will use Clock(1.0) as a default clock and will raise a warning, that it selected a default clock.]

My proposal is to add a parameter, e.g., --defaultClockPeriod=1.0, with a default value of 1.0s to set the default clock period used in the C/Cpp runtime.

[Bernhard Thiele]

Should be fixed by ​https://github.com/OpenModelica/OMCompiler/commit/0e016dc235f2d72d19081e52ac2a3db276b5c6c0

[Bernhard Thiele]

The last comment accidentally did go the wrong ticket. Ignore it.

[Rüdiger Franke]

Following the Modelica spec cited above, it should be implemented in the module SynchronousFeatures.

[Rüdiger Franke]

On the other side one might explicitly want an inferred clock, e.g. when exporting an FMU -- meaning that the code generation is the best place for inserting a default sample period into a simulator.

[Lennart Ochel]

How is it currently handled in the cpp runtime?

[Bernhard Thiele]

Replying to rfranke:

Following the Modelica spec cited above, it should be implemented in the module SynchronousFeatures.

This would correspond to set the default clock at compile time, rather than at run time. I have no strong opinion about it. Setting it at run time adds some flexibility, but doing it at compile time might have other advantages.

[Rüdiger Franke]

Both the C and the Cpp templates currently call the frontend function Expression.getClockInterval. It returns 0.0 for an unknown (inferred) clock.

The FMI export does not call this function, but generates a different modelDescription.xml for each possible clock type (integer, real, inferred, ...).

I think that the place where the CodegenC/Cpp.tpl call getClockInterval is where a default clock should be introduced.

[Rüdiger Franke]

4dbbfd4/OMCompiler and 4832d7a4/OMCompiler introduce a the default Clock(1.0) and raise a warning as proposed in the Modelica spec (see above).