anybaud.c

/*
 * Allows to set arbitrary speed for the serial device on Linux.
 * stty allows to set only predefined values: 9600, 19200, 38400, 57600, 115200, 230400, 460800.
 */
#include <stdio.h>
#include <fcntl.h>
#include <errno.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <stdarg.h>
#include <sys/ioctl.h>
#include <asm/termbits.h>

#define error_exit(f, args...)				       		       \
	printf_exit("%s: " f ": %s (code: %d)\n", __func__, ##args,	       \
						  strerror(errno), errno)

static void printf_exit(char *f, ...) {
	va_list va;

	va_start(va, f);
	vfprintf(stderr, f, va);
	va_end(va);

	exit(EXIT_FAILURE);
}

static void usage(char* argv[]) {
	printf("%s device speed\n\n"
	       "Set speed for a serial device.\n"
	       "For instance:\n"
	       "    %s /dev/ttyUSB0 75000\n", argv[0], argv[0]);
	exit(EXIT_FAILURE);
}

int main(int argc, char* argv[]) {

	int fd, speed;
	struct termios2 tio;

	setbuf(stdout, NULL);

	if (argc != 3)
		usage(argv);

	fd = open(argv[1], O_RDONLY);
	if (fd < 0)
		error_exit("opening tty");

	speed = atoi(argv[2]);

	if (ioctl(fd, TCGETS2, &tio) < 0)
		error_exit("TCGETS2 ioctl");

	tio.c_cflag &= ~CBAUD;
	tio.c_cflag |= BOTHER;
	tio.c_ispeed = speed;
	tio.c_ospeed = speed;

	if (ioctl(fd, TCSETS2, &tio) < 0)
		error_exit("TCSETS2 ioctl");
	if (ioctl(fd, TCGETS2, &tio) < 0)
		error_exit("TCGETS2 ioctl");
	close(fd);

	printf("%s speed changed to %d baud\n", argv[1], tio.c_ospeed);
	return 0;
}

Thanks, this was incredibly helpful.