Simulink Customize send component to ONLY receive event/message from external c/c++ code

Hi,

for a test project, I want to use this example by some small changes.

currently, there is a Send Component in the example, responsible to send sine wave data to a receiver component. my problem is that, this process is being done in a somehow "Scheduled" manner and even when I changed sine wave with a Constant block, it also sends the message in every time step. My goal is to create a project that messages ONLY can be sent from an external c/c++ code to the send component "Not every time step and only whenever my c/c++ code decides to send".

thanks

Answer 1

[Shubham]

Hi Jafar,

It seems that you want to modify your Simulink model to ensure a message is sent only when triggered by external C/C++ code. To achieve this, follow these steps:

1. Create the external C/C++ code.

#include "mex.h"
#include <stdbool.h>

/* External function to determine if a message should be sent */
bool shouldSendMessage() {
    static int counter = 0;
    counter++;
    return (counter % 5 == 0);
}

/* Gateway function for the MEX file */
void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[]) {
    if (nrhs != 0) {
        mexErrMsgIdAndTxt("MyToolbox:shouldSendMessage:nrhs", "No input required.");
    }
    if (nlhs != 1) {
        mexErrMsgIdAndTxt("MyToolbox:shouldSendMessage:nlhs", "One output required.");
    }

    bool result = shouldSendMessage();
    plhs[0] = mxCreateLogicalScalar(result);
}

2. Implement the "S-function" to interface with the external C/C++ code.

#define S_FUNCTION_NAME  my_sfunction
#define S_FUNCTION_LEVEL 2

#include "simstruc.h"
#include "mex.h"

static void mdlInitializeSizes(SimStruct *S) {
    ssSetNumSFcnParams(S, 0);
    if (!ssSetNumInputPorts(S, 0)) return;
    if (!ssSetNumOutputPorts(S, 1)) return;
    ssSetOutputPortWidth(S, 0, 1);
    ssSetNumSampleTimes(S, 1);
}

static void mdlInitializeSampleTimes(SimStruct *S) {
    ssSetSampleTime(S, 0, INHERITED_SAMPLE_TIME);
    ssSetOffsetTime(S, 0, 0.0);
}

static void mdlOutputs(SimStruct *S, int_T tid) {
    real_T *y = ssGetOutputPortRealSignal(S, 0);

    mxArray *lhs[1];
    mexCallMATLAB(1, lhs, 0, NULL, "external_code");

    y[0] = mxGetScalar(lhs[0]);
    mxDestroyArray(lhs[0]);
}

static void mdlTerminate(SimStruct *S) {}

#ifdef MATLAB_MEX_FILE
#include "simulink.c"
#else
#include "cg_sfun.h"
#endif

3. Compile the external C/C++ code and the "S-function" as a MEX file.

4. Connect the output of the "S-Function" block to the input of the "Send Component" in your Simulink model.

5. Run the Simulink model.

The "S-Function" block will call "shouldSendMessage" at each simulation step, sending a message only when "shouldSendMessage" returns true (every 5th step in this example).

For more information on "S-function", refer to the following MathWorks documentation link:

https://mathworks.com/help/releases/R2023b/simulink/slref/sfunction.html

Hope this helps.