int main(void)
{
    char *portname = "/dev/ttyO4";

    int fd = open (portname, O_RDWR | O_NOCTTY | O_SYNC);
    if (fd < 0)
    {
        printf ("error %d opening %s: %s", errno, portname, strerror (errno));
        return 0;
    }

    set_interface_attribs (fd, BAUD_RATE, 0);
    set_blocking (fd, 1);

    tcflush(fd, TCIOFLUSH);

    char s[] = "XBMCA";
    std::string ans = "";

    int n;

    while (true)
    {
        do {
            n = write (fd, s, sizeof(s));

            if (n < 0)
            {
                std::cout << "ERROR";
            }
        } while (n == 0);

        //write (fd, (void*)s, strlen(s));
        char buf[100];

        do {
            n = read(fd, buf, 99);

            if (n < 0 && errno != EAGAIN)
            {
                std::cout << "ERROR";
            }
            if (n < 0 && errno == EAGAIN)
            {
                continue;
            }
        } while (n == 0);

        //int b = read (fd, (void*)buf, 99);
        buf[n] = '\0';

        std::cout << buf;
        std::cout.flush();
        sleep(1);
    }

    return 0;
}