Hi, I'm trying to determine the current situation & "best practices" for setting custom baud rates. All the hardware I own, and all USB-serial ICs I know of, support baud rates beyond the set of ~15 "standard" rates defined over 20 years ago, but there still seems to be no straightforward, portable method of setting custom baud rates ! So far, I've found 3 methods that *may* be able to set custom baud rates, in *some* cases : 1- B38400 + ASYNC_SPD_CUST: (source: comments in drivers/usb/serial/ftdi_sio.c ): **** Set tty->termios->c_cflag speed to B38400 Sall TIOCSSERIAL ioctl with (struct serial_struct) set as follows: -flags & ASYNC_SPD_MASK == ASYNC_SPD_CUST -custom_divisor set to baud_base / your_new_baudrate **** Problem : some drivers don't implement TIOCSSERIAL, like ftdi_sio a few years ago, and currently also CH34* ( drivers/usb/serial/ch341.c ) Also, wasn't this the method that used to make the kernel print an unhelpful "X sets a custom speed on Y, this is deprecated" ? I remember not finding an alternate method, at the time. 2- BOTHER in drivers/tty/tty_ioctl.c , the implementation of tty_termios_baud_rate() has this: **** #ifdef BOTHER /* Magic token for arbitrary speed via c_ispeed/c_ospeed */ if (cbaud == BOTHER) return termios->c_ospeed; #endif **** Which looked promising, but according to some lore : - BOTHER isn't always/ever defined in <termios.h> ? - #include <asm/termios.h> may cause problems, and looks like a non-portable hack ? - There's a connection with "termios2" vs glibc which I'm unsure of. 3- POSIX cfsetispeed / cfsetospeed: (calling those functions with the integer value of the desired baud rate ) Its success depends on how the "speed_t" argument is implemented, so it probably won't work because of the way the Bxx flags are defined? So, what can I do ? I've looked at the code for stty and setserial, and neither will succeed in setting the speed on a CH341. This isn't a new problem of course, but I was hoping the situation would be saner, or at least have a clean solution in 2015 ! Regards, C -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
