BBB UART baud rate.

[marius.m...@gmail.com]

Hi,

I have a BeagleBone Black (rev. C) that runs Debian distro (3.8.13-bone70 Linux Kernel version), and I want to communicate via UART with some device that's using 1.5Mbaud (1500000 baud).

Since the serial communication Linux API (termios.h) don't provide such higher values, I'm using the stty utility.

This tool allows me to set some higher baud values like: 1000000, 1500000, 2000000, 2500000, etc.

The problem is that when I set the baud rate on some UART-associated port at 1500000 baud (via stty), it will actually get ~1754385 baud (568 nanoseconds per bit, measured using an scope).

Q1: Why is this happening?

Q2: How can I set the exact 1500000 baud? (+- ~5% variation would be fine).

Thanks.

[William Hermans]

https://groups.google.com/forum/#!searchin/beagleboard/peter$20hurley$20bother/beagleboard/GC0rKe6rM0g/lrHWS_e2_poJ

I have not tested this code my self, but Marlon said it worked fine for him, and the code is so very simple I do not see why It would not work . . . code is at the gist link below.

Hi Marlon,

On 07/09/2015 07:30 PM, Peter Hurley wrote:> Using the BOTHER method of setting a custom baud rate is roughly

> outlined in the stackoverflow link noted by William.
>
> I hacked up a quick test to set this baud rate in an i/o validation
> test jig and confirmed with a scope the signal period of ~173.6 us

I understand that was probably too much information :)
So I forked the github gist from the stackoverflow answer and cleaned it up.

Here's what you need to do to get this working. At the console prompt on your beaglebone:

$ # install compiler, include files, basic libraries, etc.
$ sudo apt-get install build-essential

$ # get source file from github for program that allows you to set any baud in linux
$ wget https://gist.githubusercontent.com/peterhurley/fbace59b55d87306a5b8/raw/220cfc2cb1f2bf03ce662fe387362c3cc21b65d7/anybaud.c

$ # compile program
$ gcc -o anybaud anybaud.c

$ # run program, but substitute your tty device name
$ ./anybaud /dev/ttyS4 5760


Regards,
Peter Hurley

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[William Hermans]

Additionally Marius,

There are other serial tools similar to stty there are at least fgetty, and getty, that can set buad rate too. Possibly more cmdline tools as well. That I've forgotten about . . .