/*
 * Name: dvm
 *
 * Description:
 *      A simple program to read a value from the Radio Shack
 *      digital multimeter every 60 seconds.
 *
 * Example:
 *      dvm /dev/tty02 > readings
 *
 */

#include <stdio.h>
#include <termio.h>
#include <sys/fcntl.h>
#include <unistd.h>
#include <sys/ioctl.h>

int main (int argc, char *argv[])
{
    int        m;        /* modem control lines */
    int        fd_dev;   /* FD for the open serial port */
    char       c;        /* char received from the DMM */
    struct  termios    tbuf;  /* serial line settings */

    if (argc != 2) {
        printf("Usage: %s [tty port]\n", argv[0]);
        exit(1);
    }

   if (( fd_dev = open(argv[1], O_RDWR, 0)) < 0 ) {
        printf("Unable to open tty port specified\n");
        exit(1);
    }

    /* set up the line parameters : 7,2,N */
    tbuf.c_cflag = CS7|CREAD|CSTOPB|B1200|CLOCAL;
    tbuf.c_iflag = IGNBRK;
    tbuf.c_oflag = 0;
    tbuf.c_lflag = 0;
    tbuf.c_cc[VMIN] = 1; /* character-by-character input */
    tbuf.c_cc[VTIME]= 0; /* no delay waiting for characters */
    if (tcsetattr(fd_dev, TCSANOW, &tbuf) < 0) {
        printf("%s: Unable to set device '%s' parameters\n",argv[0], argv[1]);
        exit(1);
    }

    /* Set DTR (to +12 volts) */
    m = TIOCM_DTR;
    if (ioctl(fd_dev, TIOCMSET, &m) < 0) {
        printf("%s: Unable to set '%s' modem status\n",argv[0], argv[1]);
        exit(1);
    }

    while (1) {
        write(fd_dev,"D", 1);
        do {
            read(fd_dev, &c, 1);
            write(1, &c, 1);
        } while (c != '\r');
        write(1, "\n", 1);
        sleep(60);
    }
    /* This program is rude in that it does not restore the */
    /* serial line parameters on exit. */

    exit(0);
}