Is there any way to check which baud rates are supported for a serial device on Linux?
I've poked around the
/sys/class/tty/ttyS0 directory, but I can't see anything in there that lists this type of information.
Super User is a question and answer site for computer enthusiasts and power users. It only takes a minute to sign up.Sign up to join this community
You seem to be asking two different questions.
Is there any way to check which baud rates are supported on a serial device?
The answer would depend on (1) the capabilities of the hardware, i.e. the UART/USART/SCC, and the range of divisors that the device driver can use in the baud rate generator; consult the device data sheet; (2) the frequency of the clock/oscillator connected to the serial port device; consult the board documentation.
Is there any way to check which baud rates are supported on Linux?
The one of the defined baud rates in
include/asm-generic/termbits.h for the c_cflag member of the terminal control structure is the typical method that the serial port (i.e. UART/USART) device driver receives for the baud rate configuration value.
#define B0 0000000 /* hang up */ #define B50 0000001 #define B75 0000002 #define B110 0000003 #define B134 0000004 #define B150 0000005 #define B200 0000006 #define B300 0000007 #define B600 0000010 #define B1200 0000011 #define B1800 0000012 #define B2400 0000013 #define B4800 0000014 #define B9600 0000015 #define B19200 0000016 #define B38400 0000017 #define BOTHER 0010000 #define B57600 0010001 #define B115200 0010002 #define B230400 0010003 #define B460800 0010004 #define B500000 0010005 #define B576000 0010006 #define B921600 0010007 #define B1000000 0010010 #define B1152000 0010011 #define B1500000 0010012 #define B2000000 0010013 #define B2500000 0010014 #define B3000000 0010015 #define B3500000 0010016 #define B4000000 0010017
Serial port drivers typically do not have any means of reporting/advertising which of these baud rates are actually supported/configurable/implemented. There is a capabilities value for attributes like FIFO and sleeping but not for baud rates. A driver could define an ioctl() call to configure (nonstandard) baud rates, although that would make programs using it non-portable.
From sawdust's answer, there is my solution:
for bauds in $( sed -r 's/^#define\s+B([1-9][0-9]+)\s+.*/\1/p;d' < \ /usr/include/asm-generic/termbits.h ) ;do echo $bauds stty -F /dev/ttyS0 $bauds && echo Ok. done 2>&1 | pr -at2
Will render on my host:
50 Ok. 75 Ok. 110 Ok. 134 Ok. 150 Ok. 200 Ok. 300 Ok. 600 Ok. 1200 Ok. 1800 Ok. 2400 Ok. 4800 Ok. 9600 Ok. 19200 Ok. 38400 Ok. 57600 Ok. 115200 Ok. 230400 Ok. 460800 Ok. 500000 Ok. 576000 Ok. 921600 Ok. 1000000 Ok. 1152000 Ok. 1500000 Ok. 2000000 stty: /dev/ttyS0: unable to perform 2500000 stty: /dev/ttyS0: unable to perform 3000000 stty: /dev/ttyS0: unable to perform 3500000 stty: /dev/ttyS0: unable to perform 4000000 stty: /dev/ttyS0: unable to perform
That is, but this won't mean it will work!
You have to test them with your cable and your device...
You can check the device baud rate using the "stty" command on the console:
$ stty < /dev/tty.. (where tty... is the device file you are listening)
speed 9600 baud; line = 0; -brkint -imaxbel
You can also change the baud rate with the following command:
$ sudo stty -F /dev/tty... 9600 (or whatever baud rate number)