External Functions: Reference headers in C-script to compiled dll

Question

Using Dymola 2017.

Case A) Calling an external c-script

I have had success implementing simple external c functions that have no “# include <-->” statements:

Modelica Function:

function chirp

  input Modelica.SIunits.AngularVelocity w_start;
  input Modelica.SIunits.AngularVelocity w_end;
  input Real A;
  input Real M;
  input Real t;
  output Real u "output signal";

  external "C" u=chirp(w_start,w_end,A,M,t)
    annotation(IncludeDirectory="modelica://ExternalFuncTest/Resources/Source/", Include="#include \"chirp.c\"");

end chirp;

C-script:

double chirp(double w1, double w2, double A, double M, double time)
{
  double res;
  res=A*cos(w1*time+(w2-w1)*time*time/(2*M));
    
  return res;
}

Case B) Calling an external function in a .dll file

I also have had success in calling external functions within a compiled dll:

Modelica Function:

function bessel_Jn
  "Bessel function of the 1st kind (regular cylindrical) of order n"

  extends Modelica.Icons.Function;

  input Integer n;
  input Real x;
  output Real y;

  external "C" y=gsl_sf_bessel_Jn(n,x) annotation(LibraryDirectory="modelica://ExternalFuncTest/Resources/Source/gsl-1.8/", Library="libgsl");

end bessel_Jn;

Case C) Calling an external c-script which uses functions from an external .dll via headers

What I want to do now is create a c function that does more interesting things. My current approach is to include header files in the c function that references the compiled dll (in this case a compiled version of the GNU scientific library). This example has the header (although it does not do anything for the moment).

Modelica Function:

function chirp

  input Modelica.SIunits.AngularVelocity w_start;
  input Modelica.SIunits.AngularVelocity w_end;
  input Real A;
  input Real M;
  input Real t;
  output Real u "output signal";

  external "C" u=chirp(w_start,w_end,A,M,t)
    annotation(LibraryDirectory="modelica://ExternalFuncTest/Resources/Source/gsl-1.8/", Library="libgsl",
               IncludeDirectory="modelica://ExternalFuncTest/Resources/Source/", Include="#include \"chirp.c\"");

end chirp;

C-cript:

#include <gsl/gsl_sf_bessel.h> //<-- note the additional header

double chirp(double w1, double w2, double A, double M, double time)
{
  double res;
  res=A*cos(w1*time+(w2-w1)*time*time/(2*M));
  return res;
}

When attempting to call the function above the error indicates failure to translate and nothing else due to the existence of the header file. If the header file is commented out the function will run as expected.

Please let me know if you have any insight as to how to properly go about implementing this feature. Thank you.

For reference: The image below is the path to the external c-script and .dll.

Wrong Path: Note gsl header folder is within gsl-1.8 folder

Correct Path: Note gsl header folder is at the same level as gsl-1.8 folder

UPDATE: Header works but function call causes translation to fail

I have updated the c-script to now call a function that should be handeled by the header. In its current state it won't work. Perhaps it can't find the .dll file although its specified in the modelica code? Do I have to include a load .dll command in the c-scripts?

#include <gsl/gsl_sf_bessel.h>

double chirp(double w1, double w2, double A, double M, double time)
{
  double res;
  double y;
  res=A*cos(w1*time+(w2-w1)*time*time/(2*M));
  y = gsl_sf_bessel_j0(time); // <-- Calls a function from the .dll file using the header
  return res;
}

I would have expected the last example to work (provided headers were located where I think they are). So probably either: file a bug report with Dymola (?) support or try it in another tool first to make sure. — sjoelund.se
@sjoelund.se I've added a picture to hopefully clarify what the folder structure looks like. Does this match what you expected or have I goofed? — Scott G
@sjoelund.se I think I may have found a solution by changing the location of the gsl header folder. I'll update my post above. I swear I already tried it before but it's working now though so I must have changed something else. — Scott G
I cannot reproduce the problem. However, another solution would be use #include "gsl-1.8/gsl/gsl_errno.h" instead. The difference between <> and "" for include is that "" also searches relative to the source file - which may be seen as chirp.c (so people normally use <> for system files and "" for user files). But I cannot see that it makes a difference. — Hans Olsson
You changed the location of the DLL. Did you update the LibraryDirectory? — sjoelund.se

DelmeDelmi DelmeDelmi · Accepted Answer · 2016-12-15T14:20:31

I believe this can only be resolved with relative include paths or future tools that implement future Modelica Language Specification 3.4. See https://trac.modelica.org/Modelica/ticket/2103 for the corresponding update on the Modelica Language Specification.

External Functions: Reference headers in C-script to compiled dll

3 Answers