MATLAB: C++ S-Function DYNAMICALLY_SIZED only known after mdlStart

simulinksimulink c++ s-function sfunction dynamically_sized

Is there a way to set the Input-/Outputports during mdlStart? My Problem is that i am creating an instance of an object during the mdlStart function, and until this point I can't be sure about the size of my output signal.

Of course i could already create a dummy object during mdlInitializeSizes and free the Memory at the end of the function, but this would mean quite an overhead every time this function is called.

Is there any way I could avoid this? The examples from the helpfile did not help me as this example use parameters from simulink, which are already available during the call to mdlInitializeSizes.

Thanks for helping.

Best Answer

Unfortunately, no, the Simulink Engine allocates memory for the input and output signals in time for mdlStart, so the S-function needs to specify the number/size of the inputs and outputs before mdlStart.

Related Solutions

MATLAB: How to allocate and free memory for a PWork vector in a C-MEX S-function

First, the S-Function needs to specify how many PWork vectors it needs (using ssSetNumPWork) either in mdlInitializeSizes or in mdlSetWorkWidths. Simulink calls the above functions in the S-Function at the beginning of the model initialization stage (internally we refer to this part of the initialization stage as the compile phase). Towards the end of model initialization stage (internally we refer to this part of the initialization stage as the link phase), Simulink allocates the specified number of PWorks. Upon completing the model initialization stage, Simulink calls the S-Function's mdlStart. In the mdlStart function, the S-Function can allocate memory and store a pointer to it in the PWork array. The following code snippet illustrates specifying, allocating, using, and freeing memory using PWorks.

mdlInitializeSizes(SimStruct* S) 
{ 
/* snip */
ssSetNumPWork(S, 1);
/* snip */ 
}
mdlStart(SimStruct* S) 
{ 
/* snip */
void* ptr = malloc(1024 /* number of bytes */); 
if (ptr == NULL) { 
/* report memory allocation error */ 
ssSetErrorStatus(S, "Memory allocation error"); 
return; 
} 
ssSetPWorkValue(S, 0, ptr);
/* snip */ 
}
mdlOutputs(SimStruct* S, int_T tid) 
{ 
void* ptr = ssGetPWorkValue(S, 0);
/* snip */ 
}
mdlTerminate(SimStruct* S) 
{ 
/* snip */
/* free the memory allocated in mdlStart */ 
if (ssGetPWork(S) != NULL) { 
void* ptr = ssGetPWorkVale(S,0); 
if (ptr != NULL) free(ptr); 
}
/* snip */ 
}

For a more complete example on using PWork vectors please look at the following example in the documentation.

http://www.mathworks.com/help/releases/R2009b/toolbox/simulink/sfg/bre1pj2.html#bre1ps0

MATLAB: Do I get a Port Width mismatch error in the CMEX S-function when using dynamically_sized for either the inputs or outputs

In Level 1 S-functions (Simulink 2.1 and below) the only workaround, is to either set both the input and the output to dynamically_size or both to a fixed size.

However, in Level 2 S-functions (Simulink 2.2 and above) you need to use the two new macros introduced in Level 2: mdlSetInputPortWidth and mdlSetOutputPortWidth. This is described in the S-function section of the Using Simulink User's Guide.

To fix the above code, you need to include the following after the mdlInitializeSizes subfunction:

#if defined(MATLAB_MEX_FILE)
# define MDL_SET_INPUT_PORT_WIDTH
    static void mdlSetInputPortWidth(SimStruct *S, int_T port,
                                      int_T inputPortWidth)
    {
        ssSetInputPortWidth(S,port,inputPortWidth);
        ssSetOutputPortWidth(S,port,NOUTPUT);
    }
# define MDL_SET_OUTPUT_PORT_WIDTH
    static void mdlSetOutputPortWidth(SimStruct *S, int_T port,
                                       int_T outputPortWidth)
    {
        ssSetInputPortWidth(S,port,DYNAMICALLY_SIZED);
        ssSetOutputPortWidth(S,port,NOUTPUT);
    }
#endif

Best Answer

Related Solutions

MATLAB: How to allocate and free memory for a PWork vector in a C-MEX S-function

MATLAB: Do I get a Port Width mismatch error in the CMEX S-function when using dynamically_sized for either the inputs or outputs

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