#include <sys/ioctl.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <asm/ioctls.h>
#include <errno.h>
#include <termios.h>  
 
//Control struct for setting the port in 485 mode
struct rs485_ctrl {
  unsigned short rts_on_send;
  unsigned short rts_after_sent;
  unsigned int  delay_rts_before_send;
  unsigned short enabled;
};
 
//This struct is only needed if we would like to write with ioctl()
struct rs485_wrt {
  unsigned short outc_size;
  unsigned char *outc;
};
 
int main(void)
{
  char texttosend[] = "Prova\n\r00";
  struct rs485_ctrl ctrl485;
  struct rs485_wrt io485;
  int status;
  int fd;
  char dev[] = "/dev/ttyS3";
  unsigned char buf[100];
  int size; 
  struct termios ti;
  
  //open the port
  fd = open(dev, O_RDWR); // to open as non blocking use "O_RDWR|O_NONBLOCK"
  if (fd < 0) {
    printf("ERROR! Failed to open %s\n", dev);
    return -1;
  }
 
  // Set the port in 485 mode
  ctrl485.rts_on_send = 0;
  ctrl485.rts_after_sent = 1;
  ctrl485.delay_rts_before_send = 1;
  ctrl485.enabled = 1;
  status = ioctl(fd, TIOCSERSETRS485, &ctrl485);
  if (status) {
    printf("ERROR PORT 1! TIOCSERSETRS485 failed %i", status);
    return -1;
  }
 
  // Set the port in raw mode
  tcgetattr(fd, &ti);
  ti.c_cflag |= B9600;
  ti.c_cflag |= CS8;    // 8 data bit
  ti.c_iflag |= IGNPAR; // Ignore framing errors and parity errors. 

  cfmakeraw(&ti);
  tcsetattr(fd, TCSANOW, &ti);
 
  // Writing with ioctl
  for (;;) {
    io485.outc_size = strlen(texttosend);
    io485.outc = texttosend;
    status = ioctl(fd, TIOCSERWRRS485, &io485);
    if (status != io485.outc_size) {
      printf("ERROR! TIOCSERWRRS485 failed %i (%s) \r\n", status, dev);
    }
    sleep(1);
  }
  
  // Writing with write()
  /*
  for (;;) {
    if (write(fd, texttosend, strlen(texttosend)) != strlen(texttosend)) {
      printf("ERROR! write() failed \r\n");
    }
    sleep(1);
  }
  */

#if 0 
  // Read with read()
  size = read(fd, buf, sizeof(buf)-1);
  if (size > 0) {
    printf("Read the following %d byte(s): %s \r\n", size, buf);
  }
  else if (size == 0) { 
    printf("End of file... \r\n");
  }
  else { //some error...
		// This indicates that no new data is aviable if we opened the file descriptor as non blocking
    if (errno == EAGAIN) {
      printf("No new data...\r\n");
    }
    else {
      printf("ERROR reading %s: %i %m\r\n", dev, errno);
    }
  }
#endif
 
  return 0;
}