Linux/Custom Buad Rate

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Usage

screen /dev/ttyUSB3
linux-custom-baudrate /dev/ttyUSB3 115200
linux-custom-baudrate /dev/ttyUSB3 195360
# linux-custom-baudrate: actual baudrate is 60000000 / 307 = 195439.734375

Source

linux-custom-baudrate.c:

#include <termio.h>
#include <fcntl.h>
#include <err.h>
#include <linux/serial.h>
#include <stdio.h>

static int rate_to_constant(int baudrate) {
#define B(x) case x: return B##x
	switch(baudrate) {
		B(50);     B(75);     B(110);    B(134);    B(150);
		B(200);    B(300);    B(600);    B(1200);   B(1800);
		B(2400);   B(4800);   B(9600);   B(19200);  B(38400);
		B(57600);  B(115200); B(230400); B(460800); B(500000); 
		B(576000); B(921600); B(1000000);B(1152000);B(1500000); 
	default: return 0;
	}
#undef B
}    

/* Open serial port in raw mode, with custom baudrate if necessary */
int serial_open(const char *device, int rate)
{
	struct termios options;
	struct serial_struct serinfo;
	int fd;
	int speed = 0;

	/* Open and configure serial port */
	if ((fd = open(device,O_RDWR|O_NOCTTY)) == -1)
		return -1;

	speed = rate_to_constant(rate);

	if (speed == 0) {
		/* Custom divisor */
		serinfo.reserved_char[0] = 0;
		if (ioctl(fd, TIOCGSERIAL, &serinfo) < 0)
			return -1;
		serinfo.flags &= ~ASYNC_SPD_MASK;
		serinfo.flags |= ASYNC_SPD_CUST;
		serinfo.custom_divisor = (serinfo.baud_base + (rate / 2)) / rate;
		if (serinfo.custom_divisor < 1) 
			serinfo.custom_divisor = 1;
		if (ioctl(fd, TIOCSSERIAL, &serinfo) < 0)
			return -1;
		if (ioctl(fd, TIOCGSERIAL, &serinfo) < 0)
			return -1;
		if (serinfo.custom_divisor * rate != serinfo.baud_base) {
			warnx("actual baudrate is %d / %d = %f",
			      serinfo.baud_base, serinfo.custom_divisor,
			      (float)serinfo.baud_base / serinfo.custom_divisor);
		}
	}

	fcntl(fd, F_SETFL, 0);
	tcgetattr(fd, &options);
	cfsetispeed(&options, speed ?: B38400);
	cfsetospeed(&options, speed ?: B38400);
	cfmakeraw(&options);
	options.c_cflag |= (CLOCAL | CREAD);
	options.c_cflag &= ~CRTSCTS;
	if (tcsetattr(fd, TCSANOW, &options) != 0)
		return -1;

	return fd;
}

void main(int argc, char *argv[])
{
    if (serial_open(argv[1], atoi(argv[2])) < 0)
    {
        fprintf(stderr, "failed\n");
    }
    pause();
}

Source: https://jim.sh/ftx/files/linux-custom-baudrate.c

Reference:


Compile

gcc linux-custom-baudrate.c -o linux-custom-baudrate
cp linux-custom-buadrate /usr/local/sbin/