How to fix number of steps (not time) in Matlab simulink - matlab

Question

This may be a simple question.But I couldn't find a way to go around this.I am using an s function block to input a wave signal to my algorithm.wave signal is being read from file of about 2000 points
First i started with simulation time equal to 50.Then it read only 50 points.I checked the 'tout' variable. It was 0,1,2,....50
Then i increased simulation time to 100.still result is same.only 50 points read.But tout is 0,2,4,6..50
I tried up to 10000.Whatever i do it reads 50 values only with wide time step like 0,200,400,600 etc.
Is it a problem with my s-function or simulink settings?
Here is the c s-function file
/* Give S-function a name */
#define S_FUNCTION_NAME Readip
#define S_FUNCTION_LEVEL 2
/* Include SimStruct definition and file I/O functions */
#include "simstruc.h"
#include <stdio.h>
#include <stdlib.h>
static FILE* file2;
/* Called at the beginning of the simulation */
static void mdlInitializeSizes(SimStruct *S)
{
ssSetNumSFcnParams(S, 0);
if (ssGetNumSFcnParams(S) != ssGetSFcnParamsCount(S)) {
return;
}
if (!ssSetNumOutputPorts(S, 3)) return;
ssSetNumContStates(S, 0);
ssSetNumDiscStates(S, 0);
ssSetOutputPortWidth(S, 0, 1);
ssSetOutputPortDataType(S,0,DYNAMICALLY_SIZED);
ssSetOutputPortOptimOpts(S, 0, SS_REUSABLE_AND_LOCAL);
ssSetOutputPortWidth(S, 1, 1);
ssSetOutputPortDataType(S,1,DYNAMICALLY_SIZED);
ssSetOutputPortOptimOpts(S, 1, SS_REUSABLE_AND_LOCAL);
ssSetOutputPortWidth(S, 2, 1);
ssSetOutputPortDataType(S,2,DYNAMICALLY_SIZED);
ssSetOutputPortOptimOpts(S, 2, SS_REUSABLE_AND_LOCAL);
ssSetNumPWork(S,1);
ssSetNumSampleTimes(S, 1);
}
/* Set sample times for the block */
static void mdlInitializeSampleTimes(SimStruct *S)
{
ssSetSampleTime(S, 0, CONTINUOUS_SAMPLE_TIME);
ssSetOffsetTime(S, 0, 0.0);
}
#define MDL_START /* Change to #undef to remove function */
#if defined(MDL_START)
/* Function: mdlStart ========
===============================================
* Abstract:
* This function is called once at start of model execution. If you
* have states that shou
ld be initialized once, this is the place
* to do it.
*/
static void mdlStart(SimStruct *S)
{
/*at start of model execution, open the file and store the pointer
*in the pwork vector */
void** pwork = ssGetPWork(S);
FILE *datafile;
datafile = fopen("table.data","r");
pwork[0] = datafile;
}
#endif /* MDL_START */
/* Function: mdlOutputs =======================================================
* Abstract:
* In this function, you compute the outputs of your S-function
* block. Generally outputs are placed in the output vector, ssGetY(S).
*/
static void mdlOutputs(SimStruct *S, int_T tid)
{
//get pointer to the block's output signal
real_T *y1 = ssGetOutputPortSignal(S,0);
real_T *y2 = ssGetOutputPortSignal(S,1);
real_T *y3 = ssGetOutputPortSignal(S,2);
char a[10];
char b[10];
char c[10];
/*get pointer to array of pointers, where the first element is the address
*of the open file */
void** pwork = ssGetPWork(S);
/*read a floating point number and then the comma delimiter
*store the result in y*/
fscanf(pwork[0],"%s %s %s",&a,&b,&c);
*y1=atof(a);
*y2=atof(b);
*y3=atof(c);
}
/* Function: mdlTerminate =====================================================
* Abstract:
* In this function, you should perform any actions that are necessary
* at the termination of a simulation. For example, if memory was
* allocated in mdlStart, this is the place to free it.
*/
static void mdlTerminate(SimStruct *S)
{
//close the file
void** pwork = ssGetPWork(S);
FILE *datafile;
datafile = pwork[0];
fclose(datafile);
}
/*=============================*
* Required S-function trailer *
*=============================*/
#ifdef MATLAB_MEX_FILE /* Is this file being compiled as a MEX-file? */
#include "simulink.c" /* MEX-file interface mechanism */
#else
#include "cg_sfun.h" /* Code generation registration function */
#endif

Answer 1

This appears to just be a settings issue. If you do not specify a step-size for your solver and your blocks do not indicate sample time, Simulink will choose a default of Simulation Time / 50. Simply open the Model Configuration Parameters dialog and click on solvers in the left-hand pane. If you are using a fixed-step solver, you can explicitly set the step size. If you are using a variable-step solver, you can specify the max/min step sizes.
Additionally, if you are looking to specify a discrete sample period specifically for your S-function, then you may want to look in to this link to be sure that you are implementing mdlInitializeSampleTimes as desired.

Answer 2

You need to use the fixed step discrete solver.
Set Periodic sample time constraint to 'Unconstrined'
Enter the Fixed-step size and Simulation Stop time so that you get 2000 steps.
For example 1s/step and 2000s stop time, or 0.1s/step and 200s stop time.