Serial Port 4 in TivaC not working but if I use the Port 0 it works fine in my TivaC launchpad

Hello;

I'm making a program in Simulink where I use a TivaC to send information by Serial4, but the problem is that the program runs fine for a little seconds, then the program crash. During the little time that the program runs the variables that don't have any relation with the UART 4 begins to change of values in erratic way.

I tried changing to the port 0, and the program works perfect.

This is the code in the s-function for the serial transmit:

/*
 * Include Files
 *
 */
#if defined(MATLAB_MEX_FILE)
#include "tmwtypes.h"
#include "simstruc_types.h"
#else
#include "rtwtypes.h"
#endif

/* %%%-SFUNWIZ_wrapper_includes_Changes_BEGIN --- EDIT HERE TO _END */
# ifndef MATLAB_MEX_FILE
# include <Energia.h>
# include <math.h>   
# endif
/* %%%-SFUNWIZ_wrapper_includes_Changes_END --- EDIT HERE TO _BEGIN */
/*
 * Create external references here.  
 *
 */
/* %%%-SFUNWIZ_wrapper_externs_Changes_BEGIN --- EDIT HERE TO _END */
/* extern double func(double a); */
/* %%%-SFUNWIZ_wrapper_externs_Changes_END --- EDIT HERE TO _BEGIN */

/*
 * Output functions
 *
 */
extern "C" void Radio_Link_Outputs_wrapper(const real_T *UART_1,
			const real_T *xD,
			const int_T u_width)
{
/* %%%-SFUNWIZ_wrapper_Outputs_Changes_BEGIN --- EDIT HERE TO _END */
if (xD[0] == 1){
# ifndef MATLAB_MEX_FILE  
int as=0;    
Serial4.print('$');
for (as=0;as<u_width;as=as+1){  
Serial4.print(UART_1[as],6);
     if (as!=(u_width-1)){
        Serial4.print(',');
     }
}
Serial4.println('%'); 


# endif   
}
/* %%%-SFUNWIZ_wrapper_Outputs_Changes_END --- EDIT HERE TO _BEGIN */
}

/*
  * Updates function
  *
  */
extern "C" void Radio_Link_Update_wrapper(const real_T *UART_1,
			real_T *xD,
			const int_T u_width)
{
  /* %%%-SFUNWIZ_wrapper_Update_Changes_BEGIN --- EDIT HERE TO _END */
if (xD[0] != 1){
    # ifndef MATLAB_MEX_FILE
    Serial4.begin(57600);
    # endif    
    xD[0] = 1;
}
/* %%%-SFUNWIZ_wrapper_Update_Changes_END --- EDIT HERE TO _BEGIN */
}

Do you have some idea of why the problem appears in other port less the port 0??

Thanks

Alberto