Same S-Function used twice, one works one doesn't - matlab

Question

I have a simulink model and I made a simple s-function block to add to my model and it works.
The catch if if I copy or use that same s-function twice in my model, when I run it only the last s-function called will do what it's supposed to do, the other will output a 0.
#define S_FUNCTION_NAME DivByZero
#define S_FUNCTION_LEVEL 2
#define NUMBER_OF_INPUTS 1
#define NUMBER_OF_OUTPUTS 1
#include "DivByZero.h"
#include "mex.h"
#if !defined(MATLAB_MEX_FILE)
/*
* This file cannot be used directly
*/
# error This_file_can_be_used_only_during_simulation_inside_Simulink
#endif
float32 DivByZeroInput;
float32 DivByZeroOutput;
const void * inputPorts[NUMBER_OF_INPUTS];
const void * outputPorts[NUMBER_OF_OUTPUTS];
static void mdlInitializeSizes(SimStruct *S)
{
uint8 i;
ssSetNumSFcnParams(S, 0);
if (ssGetNumSFcnParams(S) != ssGetSFcnParamsCount(S))
{
return; /* Parameter mismatch reported by the Simulink engine */
}
if (!ssSetNumInputPorts(S, NUMBER_OF_INPUTS)) return;
ssSetInputPortWidth(S, 0, 1);
ssSetInputPortDataType(S, 0, SS_SINGLE);
for (i = 0; i < NUMBER_OF_INPUTS; i++)
{
ssSetInputPortDirectFeedThrough(S, i, 1); /* Set direct feedthrough flag */
ssSetInputPortRequiredContiguous(S, i, 1); /*direct input signal access*/
}
if (!ssSetNumOutputPorts(S, NUMBER_OF_OUTPUTS)) return;
ssSetOutputPortWidth(S, 0, 1);
ssSetOutputPortDataType(S, 0, SS_SINGLE);
/* Set Sample Time */
ssSetNumSampleTimes(S, 1);
/* Specify the sim state compliance to be same as a built-in block */
ssSetSimStateCompliance(S, USE_DEFAULT_SIM_STATE);
ssSetOptions(S, SS_OPTION_ALLOW_PORT_SAMPLE_TIME_IN_TRIGSS);
ssSupportsMultipleExecInstances(S, true); //set so the s-function can be used in a for each subsystem block
}
static void mdlInitializeSampleTimes(SimStruct *S)
{
/* Inherits sample time from the driving block */
ssSetSampleTime(S, 0, INHERITED_SAMPLE_TIME);
ssSetOffsetTime(S, 0, 0.0);
ssSetModelReferenceSampleTimeDefaultInheritance(S);
}
#define MDL_START
#if defined(MDL_START)
static void mdlStart(SimStruct *S)
{
uint8 i;
/* Save Input ports */
for (i = 0; i < NUMBER_OF_INPUTS; i++)
{
inputPorts[i] = ssGetInputPortSignal(S, i);
}
/* Save Output ports */
for (i = 0; i < NUMBER_OF_OUTPUTS; i++)
{
outputPorts[i] = ssGetOutputPortRealSignal(S, i);
}
}
#endif
static void mdlOutputs(SimStruct *S, int_T tid)
{
memcpy(&DivByZeroInput, inputPorts[0], sizeof(DivByZeroInput));//gets the input port info
if (fabs(DivByZeroInput) > 0.00001f)
{
DivByZeroOutput = DivByZeroInput;
}
else
{
if (DivByZeroInput >= 0.0f)
{
DivByZeroOutput = 0.00001f;
}
else
{
DivByZeroOutput= -0.00001f;
}
}
memcpy(outputPorts[0], &DivByZeroOutput, sizeof(DivByZeroOutput));//sets the output port
}
static void mdlTerminate(SimStruct *S)
{
/* MODEL TERMINATE */
}
/* END OF TEMPLATE */
#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
The s-function is supposed to provide a simple division by zero protection as you can see from the code.
In the image below, if I delete S-Function1, S-Function will then work as intended.
I tried putting it in a library block and just put 2 library blocks and I got the same result

Answer 1

You are defining these variables:
float32 DivByZeroInput;
float32 DivByZeroOutput;
const void * inputPorts[NUMBER_OF_INPUTS];
const void * outputPorts[NUMBER_OF_OUTPUTS];
These variables are shared across both instances, which means both S-Functions write to the same output addresses.
Side note: Do you really have to use an S-Function? Creating the same from a few native simulink blocks is probably much easier.