Simulink model not plotting my Sine

Hi, I'm trying to build a simulink model working with S-function written in C. However, when I run the Simulink model, the scope is just a straight line, but it's suppose to be a sine wave. I used Legacy Code Toolbox to generate my S-function. My header file is just

int Sine_value(double amplitude, double vitesse_ang, double phase);

and my main file is

#include "Sine_value.h"

#include <math.h>

int Sine_value(double amplitude,

double vitesse_ang,

double phase,

)

{

int t[101];

int i;

int y0[101]

for (i = 0; i <= 100 ; i++) {

t[i] = i;

y0[i] = amplitude * sin(vitesse_ang * t[i] + phase);

}

return *y0;

}

To compile these file into the S-function, i used all these commands from the Legacy Code Toolbox :

def = legacy_code('initialize')

def.SFunctionName = 'S_function1'

def.OutputFcnSpec = 'y0 = Sine_value(double u1, double u2, double u3)'

def.HeaderFiles = {'Sine_value.h'}

def.SourceFiles = {'main.c'}

legacy_code('sfcn_cmex_generate', def)

legacy_code('compile', def)

I also attached all my files required.

Answer 1

[Fangjun Jiang]

I understand this might be just an exercise to learn Legacy Code Toolbox and S-function, but there are a couple of things wrong

1. I would think it would be wrong to specify the returned sine value to be an integer
2. Once the s-function is compiled and built, it will be executed at every simulation step. With this in mind, you would need the C function just calculate one value, y=sin(x), and leave the rest to Simulink. Calculating the full cycle of sine wave in C makes it impossible to be used to build the s-function.

[Pierre-Olivier Desrosiers]

Hi Fangjun, thanks for the answer. However, I've got some follow-up questions.

1) Instead of returning an integer, what should I return as a type ?

2) As i understood, I just need to return one value, because after each step, it will "save" a new value ? My question is : How can I get ALL the output values to plot them ?

[Fangjun Jiang]

1. Double
2. Make a simple Simulink model, Clock block, feed to a Sine Wave block and then feed to a Scope block. Run simulation and you will see the sine wave. You can also log the data and plot the wave in MATLAB.
3. Develop your s-function and then replace the Sine Wave block.

[Pierre-Olivier Desrosiers]

Hi Fangjun, I had a last question. How do I call my time constant in my C function so my simulink model take the step time parameters to calculate the sine wave ?

[Pierre-Olivier Desrosiers]

Found my answer here :

https://www.mathworks.com/matlabcentral/answers/5999-how-do-i-use-simulation-time-as-realtime-changing-variable