setserialsignal.c

《嵌入式Linux－硬件

/*
 * setSerialSignal v0.1 9/13/01
 * www.embeddedlinuxinterfacing.com
 *
 *
 * The original location of this source is
 * http://www.embeddedlinuxinterfacing.com/chapters/06/setSerialSignal.c
 *
 * This program is free software; you can redistribute it and/or modify 
 * it under the terms of the GNU Library General Public License as 
 * published by the Free Software Foundation; either version 2 of the 
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but 
 * WITHOUT ANY WARRANTY; without even the implied warranty of 
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public 
 * License along with this program; if not, write to the 
 * Free Software Foundation, Inc.,
 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */

/* setSerialSignal
 * setSerialSignal sets the DTR and RTS serial port control signals.
 * This program queries the serial port status then sets or clears
 * the DTR or RTS bits based on user supplied command line setting.
 *
 * setSerialSignal clears the HUPCL bit. With the HUPCL bit set, 
 * when you close the serial port, the Linux serial port driver 
 * will drop DTR (assertion level 1, negative RS-232 voltage). By
 * clearing the HUPCL bit, the serial port driver leaves the 
 * assertion level of DTR alone when the port is closed. 
 */

/*
gcc -o setSerialSignal setSerialSignal.c
*/


#include <sys/ioctl.h>
#include <fcntl.h>
#include <termios.h>

/* we need a termios structure to clear the HUPCL bit */
struct termios tio;

int main(int argc, char *argv[])
{
  int fd;
  int status;

  if (argc != 4)
  {
    printf("Usage: setSerialSignal port                  DTR RTS\n");
    printf("Usage: setSerialSignal /dev/ttyS0|/dev/ttyS1 0|1 0|1\n");
    exit( 1 );
  }

  if ((fd = open(argv[1],O_RDWR)) < 0)
  {
    printf("Couldn't open %s\n",argv[1]);
    exit(1);
  }

  tcgetattr(fd, &tio);          /* get the termio information */
  tio.c_cflag &= ~HUPCL;        /* clear the HUPCL bit */
  tcsetattr(fd, TCSANOW, &tio); /* set the termio information */

  ioctl(fd, TIOCMGET, &status); /* get the serial port status */

  if ( argv[2][0] == '1' )      /* set the DTR line */
    status &= ~TIOCM_DTR;
  else
    status |= TIOCM_DTR;

  if ( argv[3][0] == '1' )      /* set the RTS line */
    status &= ~TIOCM_RTS;
  else
    status |= TIOCM_RTS;

  ioctl(fd, TIOCMSET, &status); /* set the serial port status */

  close(fd);                    /* close the device file */
}