termios.c

#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

#ifdef USE_TERMIOS2
#include <asm/termbits.h>
#include <sys/ioctl.h>

typedef struct termios2 termios_t;

static int tcgetattr(int fd, termios_t *tio)
{
    return ioctl(fd, TCGETS2, tio);
}

static int tcsetattr(int fd, int actions, const termios_t *tio)
{
    unsigned long request;

    switch (actions) {
    case TCSANOW:
        request = TCSETS2;
        break;
    case TCSADRAIN:
        request = TCSETSW2;
        break;
    case TCSAFLUSH:
        request = TCSETSF2;
        break;
    default:
        errno = EINVAL;
        return -1;
    }

    return ioctl(fd, request, tio);
}

static int set_speed(termios_t *tio, unsigned int baudrate)
{
    tio->c_cflag &= ~CBAUD;
    tio->c_cflag |= BOTHER;
    tio->c_ispeed = baudrate;
    tio->c_ospeed = baudrate;

    return 0;
}
#else
#include <termios.h>

typedef struct termios termios_t;

static int set_speed(termios_t *tio, unsigned int baudrate)
{
    speed_t speed;

    switch (baudrate) {
    case 9600:
        speed = B9600;
        break;
    case 19200:
        speed = B19200;
        break;
    case 38400:
        speed = B38400;
        break;
    case 57600:
        speed = B57600;
        break;
    case 115200:
        speed = B115200;
        break;
    default:
        errno = EINVAL;
        return -1;
    }

    if (cfsetispeed(tio, speed) < 0 || cfsetospeed(tio, speed) < 0)
        return -1;

    return 0;
}
#endif

static int configure_serial(int fd, unsigned int baudrate)
{
    termios_t tio;

    if (tcgetattr(fd, &tio) < 0)
        return -1;

    if (set_speed(&tio, baudrate) < 0)
        return -1;

    tio.c_cflag &= ~(PARENB | CSTOPB | CSIZE);
    tio.c_cflag |= CS8 | CLOCAL | CREAD;

    tio.c_lflag &= ~(ECHO | ECHONL | ICANON | IEXTEN | ISIG);
    tio.c_iflag &= ~(IGNBRK | BRKINT | ICRNL | INLCR |
                     PARMRK | INPCK | ISTRIP | IXON);
    tio.c_oflag &= ~OPOST;
    tio.c_cc[VMIN] = 1;
    tio.c_cc[VTIME] = 0;

    return tcsetattr(fd, TCSANOW, &tio);
}

int main(int argc, char **argv)
{
    char *end;
    unsigned long value;
    int fd;
    int rc;

    if (argc != 3) {
        fprintf(stderr, "Usage: %s DEVICE BAUDRATE\n", argv[0]);
        return EXIT_FAILURE;
    }

    errno = 0;
    value = strtoul(argv[2], &end, 10);
    if (errno != 0 || *end != '\0' || value > 0xffffffffUL) {
        fprintf(stderr, "Invalid baud rate: %s\n", argv[2]);
        return EXIT_FAILURE;
    }

    fd = open(argv[1], O_RDWR | O_NOCTTY);
    if (fd < 0) {
        perror("open");
        return EXIT_FAILURE;
    }

    rc = configure_serial(fd, (unsigned int)value);
    if (rc < 0)
        perror("configure_serial");

    if (close(fd) < 0) {
        perror("close");
        return EXIT_FAILURE;
    }

    return rc == 0 ? EXIT_SUCCESS : EXIT_FAILURE;
}