Converting Level-1 C MEX S-Functions to Level-2

Guidelines for Converting Level-1 C MEX S-Functions to Level-2

Level-2 S-functions were introduced with Simulink version 2.2. Level-1 S-functions refer to S-functions that were written to work with Simulink version 2.1 and previous releases. Level-1 S-functions are compatible with Simulink version 2.2 and subsequent releases; you can use them in new models without making any code changes. However, to take advantage of new features in S-functions, Level-1 S-functions must be updated to Level-2 S-functions. Here are some guidelines:

• Start by looking at simulink/src/sfunctmpl_doc.c. This template S-function file concisely summarizes Level-2 S-functions.

• At the top of your S-function file, add this define:

  #define S_FUNCTION_LEVEL 2
  

• Update the contents of mdlInitializeSizes. In particular, add the following error handling for the number of S-function parameters:

  ssSetNumSFcnParams(S, NPARAMS); /*Number of expected parameters*/
  if (ssGetNumSFcnParams(S) != ssGetSFcnParamsCount(S)) {
  	/* Return if number of expected != number of actual parameters */
    	return;
  }
  Set up the inputs using: 
  if (!ssSetNumInputPorts(S, 1)) return; /*Number of input ports */
  ssSetInputPortWidth(S, 0, width);      /* Width of input 
                                            port one (index 0)*/ 
  ssSetInputPortDirectFeedThrough(S, 0, 1); /* Direct feedthrough
                                               or port one */
  ssSetInputPortRequiredContiguous(S, 0);
  Set up the outputs using:
  if (!ssSetNumOutputPorts(S, 1)) return;
  ssSetOutputPortWidth(S, 0, width);     /* Width of output port
                                            one (index 0) */
  

• If your S-function has a nonempty mdlInitializeConditions, update it to the following form:

  #define MDL_INITIALIZE_CONDITIONS
  static void mdlInitializeConditions(SimStruct *S)
  {
  }
  

  Otherwise, delete the function.

  • Access the continuous states using ssGetContStates. The ssGetX macro has been removed.

  • Access the discrete states using ssGetRealDiscStates(S). The ssGetX macro has been removed.

  • For mixed continuous and discrete state S-functions, the state vector no longer consists of the continuous states followed by the discrete states. The states are saved in separate vectors and hence might not be contiguous in memory.

• The mdlOutputs prototype has changed from

  static void mdlOutputs( real_T *y, const real_T *x, 
  	const real_T *u, SimStruct *S, int_T tid)
  

  to

  static void mdlOutputs(SimStruct *S, int_T tid)
  

  Since y, x, and u are not explicitly passed in to Level-2 S-functions, you must use

  • ssGetInputPortSignal to access inputs

  • ssGetOutputPortSignal to access the outputs

  • ssGetContStates or ssGetRealDiscStates to access the states

• The mdlUpdate function prototype has changed from

  void mdlUpdate(real_T *x, real_T *u, Simstruct *S, int_T tid)
  

  to

  void mdlUpdate(SimStruct *S, int_T tid)
  

• If your S-function has a nonempty mdlUpdate, update it to this form:

  #define MDL_UPDATE
  static void mdlUpdate(SimStruct *S, int_T tid)
  {
  }
  

  Otherwise, delete the function.

• If your S-function has a nonempty mdlDerivatives, update it to this form:

  #define MDL_DERIVATIVES
  static void mdlDerivatives(SimStruct *S)
  {
  }
  

  Otherwise, delete the function.

• Replace all obsolete SimStruct macros. See Obsolete Macros for a complete list of obsolete macros.

• When converting Level-1 S-functions to Level-2 S-functions, you should build your S-functions with full (i.e., highest) warning levels. For example, if you have gcc on a UNIX^[1] system, use these options with the mex utility.

  mex CC=gcc CFLAGS=-Wall sfcn.c
  

  If your system has Lint, use this code.

  lint -DMATLAB_MEX_FILE -I<matlabroot>/simulink/include 
      -Imatlabroot/extern/include sfcn.c 
  

  On a PC, to use the highest warning levels, you must create a project file inside the integrated development environment (IDE) for the compiler you are using. Within the project file, define MATLAB_MEX_FILE and add

  matlabroot/simulink/include 
  matlabroot/extern/include 
  

  to the path (be sure to build with alignment set to 8).

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Obsolete Macros

The following macros are obsolete. Replace each obsolete macro with the macro specified in the following table.

^[1] UNIX is a registered trademark of The Open Group in the United States and other countries.

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Debugging C MEX S-Functions

Creating C++ S-Functions

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