// testserial.c

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

int main(int argc, char *argv[])
{
    // const int rts_bit = TIOCM_RTS;
    // const int dtr_bit = TIOCM_DTR;
    int i, fd, flags;

    if (argc != 2) {
        fprintf(stderr, "Usage: testserial /dev/cua0\n");
        return 1;
    }
    if ((fd = open(argv[1], O_RDWR | O_NDELAY)) < 0) {
        perror("testserial");
        return 1;
    }
    // Now DTR and RTS should be high
    // ioctl(fd, TIOCMBIS, &rts_bit);  // set   RTS (high)
    // ioctl(fd, TIOCMBIC, &rts_bit);  // clear RTS (low)
    // ioctl(fd, TIOCMBIS, &dtr_bit);  // set   DTR (high)
    // ioctl(fd, TIOCMBIC, &dtr_bit);  // clear DTR (low)
    for (i = 0; i < 100; i++) {
        ioctl(fd, TIOCMGET, &flags);
        printf("DSR = %4s, CTS = %4s\n",
               (flags & TIOCM_DSR) ? "high" : "low",
               (flags & TIOCM_CTS) ? "high" : "low");
        sleep(1);           // in seconds
        // usleep(100000);  // in microseconds
    }
    close(fd);  // close, or just terminate this process
    // Now DTR and RTS should be low
    return 0;
}