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Writing Noninlined S-Functions

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About Noninlined S-Functions Guidelines for Writing Noninlined S-Functions Noninlined S-Function Parameter Type Limitations

About Noninlined S-Functions

Noninlined S-functions are identified by the absence of an sfunction.tlc file for your S-function. The filename varies depending on your platform. For example, on a 32–bit Microsoft Windows system, the file name would be sfunction.mexw32. Type mexext in the MATLAB Command Window to see which extension your system uses.

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Guidelines for Writing Noninlined S-Functions

• The MEX-file cannot call MATLAB functions.

• If the MEX-file uses functions in the MATLAB External Interface libraries, include the header file cg_sfun.h instead of mex.h or simulink.c. To handle this case, include the following lines at the end of your S-function:

  #ifdef MATLAB_MEX_FILE /* Is this file being compiled as a MEX-file? */
  #include "simulink.c"  /* MEX-file interface mechanism */
  #else
  #include "cg_sfun.h"   /* Code generation registration function */
  #endif
  

• Use only MATLAB API function that the code generator supports, which include:

  mxGetEps

  mxGetInf

  mxGetM

  mxGetN

  mxGetNaN

  mxGetPr

  mxGetScalar

  mxGetString

  mxIsEmpty

  mxIsFinite

  mxIsInf

• MEX library calls are not supported in generated code. To use such calls in MEX-file and not in the generated code, conditionalize the code as follows:

  #ifdef MATLAB_MEX_FILE
  #endif
  

• Use only full matrices that contain only real data.

• Do not specify a return value for calls to mxGetString . If you do specify a return value, the MEX-file will not compile correctly. Instead, use the function's second input argument, which returns a pointer to a string.

• Make sure that the #define s-function_name statement is correct. The S-function name that you specify must match the S-function's filename.

• Use the data types real_T and int_T instead of double and int, if possible. The data types real_T and int_T are more generic and can be used in multiple environments.

• Provide the Real-Time Workshop build process with the names of all modules used to build the S-function. You can do this by using the Real-Time Workshop template make file or the set_param function. For example, suppose you build your S-function with the following command:

  mex sfun_main.c sfun_module1.c sfun_module2.c

  You can then use the following call to set_param to include all the required modules:

  set_param(sfun_block, "SFunctionModules","sfun_module1 sfun_module2')

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Noninlined S-Function Parameter Type Limitations

Parameters to noninlined S-functions can be of the following types only:

• Double precision

• Characters in scalars, vectors, or 2-D matrices

For more flexibility in the type of parameters you can supply to S-functions or the operations in the S-function, inline your S-function and consider using an mdlRTW S-function routine.

Use of other functions from the MATLAB matrix.h API or other MATLAB APIs, such as mex.h and mat.h, is not supported. If you call unsupported APIs from an S-function source file, compiler errors occur. See the file matlabroot/rtw/c/src/rt_matrx.h(.c) for details on supported MATLAB API functions.

If you use mxGetPr on an empty matrix, the function does not return NULL; rather, it returns a random value. Therefore, you should protect calls to mxGetPr with mxIsEmpty.

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Introduction to S-Functions for Code Generation

Writing Wrapper S-Functions

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