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

dynamicfixedportsimulink

Why do I get a Port Width mismatch error in my CMEX S-function when using dynamically_sized for either my inputs or outputs? The other input is set to a fixed value. For example, in my Level 2 S-function I have the following:

if (!ssSetNumInputPorts(S, 1)) return;
      ssSetInputPortWidth(S, 0, DYNAMICALLY_SIZED);
      ssSetInputPortDirectFeedThrough(S, 0, 1);
if (!ssSetNumOutputPorts(S, 2)) return;
      ssSetOutputPortWidth(S, 0, NOUTPUT);              
      ssSetOutputPortWidth(S, 1, NOUTPUT);

where NOUTPUT was defined as 22.

However, when I run the model, I receive errors that look like the following:

 --> Port width mismatch. Output Port 1 of 'untitled/Subsystem/In1' has a width of 12.
 --> Input Port 1 of 'untitled/Subsystem/S-function' has a width of 22

How can I get around this?

Best Answer

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

Related Solutions

MATLAB: Is there an example of dynamically sized input ports with different widths in a C-MEX S-function

Here is an example showing how to write a C-MEX S-function with dynamically sized input ports that accepts 1-D (vector) signals with different widths in Simulink 6.2 (R14SP2).

In Level 2 S-functions you need to use the two new methods: mdlSetInputPortWidth and mdlSetOutputPortWidth. This is described in the S-function section of the Using Simulink User's Guide.

If you open up the attached S-function source file, you will notice the following lines after mdlInitializeSizes:

#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);
    }
# define MDL_SET_OUTPUT_PORT_WIDTH
    static void mdlSetOutputPortWidth(SimStruct *S, int_T port,int_T outputPortWidth)
    {
        ssSetOutputPortWidth(S,port,outputPortWidth);
    }
#endif

These methods are called with the candidate widths for dynamically sized ports. If the proposed widths are acceptable, the methods proceed to set the actual ports widths using ssSetInputPortWidth and ssSetOutputPortWidth.

MATLAB: Dynamically sized IO ports in simulink

The code above is mostly right, but there are some minor changes that you will need to make:

The calls to "mdlSetOutputPortWidth" and "mdlSetInputPortWidth" can occur for any port that was originally set as dynamically typed, even if was assigned a dimension later on. As a result, you should confirm that the output port is still dynamically typed before you assign the output port dimension in "mdlSetInputPortWidth". If it's still dynamically typed, assign it. If it isn't check to see if the output port dimensions match what you would have assigned. If not, throw an error.
The "mdlSetOutputPortWidth" should be a mirror-image/reverse of your "mdlSetInputPortWidth" function. People often mistakenly assume that dimensions only propagate "downstream", but it is entirely possible that your block's output port dimension gets assigned first. In this case, you should assign that dimension to the second input port as well.
"mdlSetDefaultPortDimensionInfo" gets called if any of the ports are still dynamically typed, so it is incorrect to assume that it means that all of the ports are still unspecified. Therefore, instead of just assigning dimensions to all of the ports, you should check each one to confirm that it is still dynamically typed, and only assign dimensions in that case.

Best Answer

Related Solutions

MATLAB: Is there an example of dynamically sized input ports with different widths in a C-MEX S-function

MATLAB: Dynamically sized IO ports in simulink

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