#include <termios.h>
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/signal.h>
#include <sys/types.h>

#define BAUDRATE B9600

#ifdef LINUX
#define MODEMDEVICE "/dev/cua0"
#endif

#ifdef WINDOWS
#define MODEMDEVICE "/dev/com1"
#endif

#define _POSIX_SOURCE 1 /* POSIX compliant source */
#define FALSE 0
#define TRUE 1

volatile int STOP=FALSE; 

void signal_handler_IO (int status);   /* definition of signal handler */
int wait_flag=TRUE;                    /* TRUE while no signal received */

main()
{
  int fd,c, res;
  struct termios oldtio,newtio;
  struct sigaction saio;           /* definition of signal action */
  char buf[255];
  
  /* open the device to be non-blocking (read will return immediatly) */
  fd = open(MODEMDEVICE, O_RDWR | O_NOCTTY | O_NONBLOCK);
  if (fd <0) {perror(MODEMDEVICE); exit(-1); }
  
  /* install the signal handler before making the device asynchronous */
  saio.sa_handler = signal_handler_IO;
    saio.sa_mask = 0;
  saio.sa_flags = 0;
/*  saio.sa_restorer = NULL; */
  sigaction(SIGIO,&saio,NULL);
  
  /* allow the process to receive SIGIO */
  fcntl(fd, F_SETOWN, getpid());
  /* Make the file descriptor asynchronous (the manual page says only 
     O_APPEND and O_NONBLOCK, will work with F_SETFL...) */
  fcntl(fd, F_SETFL, FASYNC);
  
  tcgetattr(fd,&oldtio); /* save current port settings */
  /* set new port settings for canonical input processing */
  newtio.c_iflag = 0; /* input modes */
  newtio.c_oflag = 0; /* output modes */
  newtio.c_cflag = 0; /* control modes */
  newtio.c_lflag = 0; /* local modes */
  
  newtio.c_cflag = BAUDRATE | CS8 | CSTOPB | CREAD;
  newtio.c_cflag &= ~PARENB;
  newtio.c_iflag = IGNPAR | ICRNL | IXON | IXOFF;
  newtio.c_cc[VMIN]=1;
  newtio.c_cc[VTIME]=0;
  tcflush(fd, TCIFLUSH);
  tcsetattr(fd,TCSANOW,&newtio);
  
  /* loop while waiting for input. normally we would do something
     useful here */ 
  c = 'U';
  while (STOP==FALSE) 
    {
      printf(".\n");
/*        usleep(100000); */
      write(fd, &c, 1);
      /* after receiving SIGIO, wait_flag = FALSE, input is available
	 and can be read */
      if (wait_flag==FALSE) { 
	res = read(fd,buf,255);
	buf[res]=0;
	printf(":%s:%d\n", buf, res);
	if (res==1) STOP=TRUE; /* stop loop if only a CR was input */
	wait_flag = TRUE;      /* wait for new input */
      }
    }
  /* restore old port settings */
  tcsetattr(fd,TCSANOW,&oldtio);
}

/***************************************************************************
 * signal handler. sets wait_flag to FALSE, to indicate above loop that     *
 * characters have been received.                                           *
 ***************************************************************************/

void signal_handler_IO (int status)
{
  printf("received SIGIO signal.\n");
  wait_flag = FALSE;
}