Signal handling for 3 serial interrupt.

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <termios.h>
#include <stdio.h>
#include<sys/signal.h>
#include<sys/ioctl.h>
        
#define BAUDRATE 	B9600
#define Modem		"/dev/ttyAM1"
#define _POSIX_SOURCE 1 /* POSIX compliant source */
#define FALSE 0
#define TRUE 1

/********************************************  Functions Prototype  *****************************************************/
void Modem_Interface(void);
void sig_handler(int status);
void serial_cnfg(void);
void modemdelay(void);     
void modemdelay1(void);

/*************************************************************************************************************************/

/*************************************************  Structures  **********************************************************/
struct termios oldtio,newtio;
struct termios oldtio1,newtio1;

/*************************************************************************************************************************/

/**********************************************  Global Variables  *******************************************************/

int FD_Printer, FD_Modem, FD_CM;
unsigned char sig_flag;
int data;
int fd,cashfd,c, res,cntr=0,virus=0;
unsigned int CM_rply_Cntr=0;
char CM_rply_Buf[250];
char rx_data,rx_cntr=0;

/*************************************************************************************************************************/


void sig_handler(int status)
{
	read(FD_Modem,&rx_data,1);
	//read(FD_Modem,CM_rply_Buf,100);
	//CM_rply_Buf[rx_cntr++]=rx_data; 
	printf("rx_data=%c\n",rx_data);
}


void modemdelay(void)
{
	unsigned int i=0,j;
	for(i=0;i<5632;i++)
		for(j=0;j<4234;j++);
}

void modemdelay1(void)
{
	unsigned int i=0,j;
	for(i=0;i<632;i++)
		for(j=0;j<234;j++);
}



void serial_cnfg(void)
{
	struct sigaction sa;
	
	sa.sa_handler	= sig_handler;
	sa.sa_flags	= 0;
	sa.sa_restorer	= NULL;
	
	sigemptyset(&sa.sa_mask);
	sigaction(SIGIO,&sa,NULL);
	
	fcntl(FD_Modem,F_SETOWN,getpid());
      fcntl(FD_Modem,F_SETFL,FASYNC);
}

void Modem_Interface(void)
  {
       
	char cmd[]="AT",data,enter=0x0D;
	unsigned int i=0;
	printf("Transmitting \n");
	while(cmd[i]!='\0')
	{
		data=cmd[i++];
		write(FD_Modem,&data,1);
	}

	write(FD_Modem,0x0D,1);
}


int main(void)
{
	unsigned int i;
	
	while(1)
      {	
       	
	  FD_Printer = open(Printer, O_WRONLY | O_NOCTTY );                 
        if (FD_Printer <0) {perror(Printer); exit(-1); }
        
	  FD_Modem = open(Modem, O_RDWR | O_NOCTTY );                 //for modem
        if (FD_Modem <0) {perror(Modem); exit(-1); }
        
        serial_cnfg();
      
        tcgetattr(FD_Modem,&oldtio); 
        bzero(&newtio, sizeof(newtio));
        
        newtio.c_cflag       = BAUDRATE | CRTSCTS | CS8 | CLOCAL | CREAD;
        newtio.c_iflag 	     = IGNPAR; 
        newtio.c_oflag 	     = 0;
        newtio.c_lflag       = 0;   /* set input mode (non-canonical, no echo,...) */
        newtio.c_cc[VTIME]   = 2;   /* inter-character timer unused */
                
        tcflush(FD_Modem, TCIFLUSH);
        tcsetattr(FD_Modem,TCSANOW,&newtio);
        
        modemdelay();  
              	
        for(i=0;i<248;i++)
        	CM_rply_Buf[i]='\0';
        		
        rx_cntr=0;
        rx_data='\0';
	
        //printf("\nIn Modem_Interface");
        Modem_Interface();

	  modemdelay();  
	  modemdelay(); 
			
 	}
      
	  tcsetattr(FD_Modem,TCSANOW,&oldtio);
    	  return 0;
                
 
}