Mac only C code to reboot an ESP32 device into bootloader mode

device-bootloader.c

/*
 * This code works on my Mac, developed in conjuntion with a logic analyzer.
 */

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

static char *prog;

void usage(void)
{
    fprintf(stderr, "Usage: %s <device>\n", prog);
    exit(1);
}

int main(int ac, char **av)
{
    prog = av[0];

    if (ac < 2) {
        fprintf(stderr, "%s: requires device path argument\n", prog);
        usage();
    }

    int fd = open(av[1], O_RDWR | O_NOCTTY | O_NDELAY);
    if (fd < 0) {
        fprintf(stderr, "%s: failed to open %s because: %s\n", prog, av[1], strerror(errno));
        usage();
    }

    struct termios options;
    fcntl(fd, F_SETFL, 0);
    tcgetattr(fd, &options);
    cfsetispeed(&options, B115200);
    cfsetospeed(&options, B115200);

    printf("Configuring port now\n");

    options.c_cflag |= (CLOCAL | CREAD | CRTSCTS);
    options.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG);
    options.c_oflag &= ~OPOST;
    options.c_cc[VMIN] = 0;
    options.c_cc[VTIME] = 10;
    tcsetattr(fd, TCSANOW, &options);

    int status;
    if (ioctl(fd, TIOCMGET, &status)) {
        fprintf(stderr, "%s: TIOCMGET failed because %s\n", prog, strerror(errno));
        usage();
    }

    printf("got status: %x\n", status);
    printf("status & TIOCM_DTR: %d\n", status & TIOCM_DTR);
    printf("status & TIOCM_DSR: %d\n", status & TIOCM_DSR);
    printf("status & TIOCM_RTS: %d\n", status & TIOCM_RTS);
    printf("status & TIOCM_CTS: %d\n", status & TIOCM_CTS);
    sleep(1);

    // Step | DTR | RTS
    // 1    | 1   | 1
    // 2    | 0   | 0
    // 3    | 1   | 0
    // 4    | 0   | 1

    // Logic analyzer shows that set bits in the ioctl
    // are actually digital low -- thus the XORing
    // These same steps without the XORing will do a regular
    // reboot
    status = 6; // step 1: DTR & RTS high
    status ^= 6;
    ioctl(fd, TIOCMSET, &status);

    status = 0; // step 2: DTR & RTS low
    status ^= 6;
    ioctl(fd, TIOCMSET, &status);

    status = 2; // step 3: DTR high, RTS low
    status ^= 6;
    ioctl(fd, TIOCMSET, &status);

    status = 4; // step 4: DTR low, RTS high
    status ^= 6;
    ioctl(fd, TIOCMSET, &status);

    usleep(50000);

    status = 6; // normal state: DTR & RTS high
    status ^= 6;
    ioctl(fd, TIOCMSET, &status);

    printf("The device should be in bootloader mode\n");

    return 0;
}