Open Serial port and select DTR/RTS pins high/low

gistfile1.txt

# LICENSE: MIT
# WARN: AI tool assisted
# INFO: seems like on my USB controller both are high while port open, then low. 

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

int main(int argc, char *argv[]) {
    if (argc != 4) {
        fprintf(stderr, "Usage: %s <device> <RTS|DTR> <on|off>\n", argv[0]);
        return EXIT_FAILURE;
    }

    // Determine control line
    int line;
    if (strcmp(argv[2], "RTS") == 0) {
        line = TIOCM_RTS;
    } else if (strcmp(argv[2], "DTR") == 0) {
        line = TIOCM_DTR;
    } else {
        fprintf(stderr, "Invalid control line\n");
        return EXIT_FAILURE;
    }

    // Determine operation
    unsigned int cmd;
    if (strcmp(argv[3], "on") == 0) {
        cmd = TIOCMBIS;
    } else if (strcmp(argv[3], "off") == 0) {
        cmd = TIOCMBIC;
    } else {
        fprintf(stderr, "Invalid state\n");
        return EXIT_FAILURE;
    }

    // Open device
    int fd = open(argv[1], O_RDWR | O_NOCTTY);
    if (fd == -1) {
        perror("Open failed");
        return EXIT_FAILURE;
    }

    // Execute control operation
    if (ioctl(fd, cmd, &line) == -1) {
        perror("Control failed");
        fprintf(stderr, "See https://tldp.org/HOWTO/Serial-HOWTO-16.html");
        close(fd);
        return EXIT_FAILURE;
    }

    usleep(200000000);
    close(fd);
    return EXIT_SUCCESS;
}