Re: Configuration of the RGA200 communication baud rate

[Érico Nogueira Rolim via Tech-talk <tech-talk at aps.anl.gov>]

Just something to note if anyone wishes to use that post as reference (and the recent glibc support isn't enough). It mentions an issue with including kernel headers:

> I ran into some #include hell with asm/termios.h, especially if I already had the normal termios.h included elsewhere, so you might have to copy relevant struct definitions into your own code if you can’t get it to work (I know, nasty!). The other thing to keep in mind is that the definition of NCCS might be different between your libc and kernel, so you need to make sure you’re using the kernel’s definition of NCCS. I believe asm/termbits.h has the correct NCCS and structures defined.

The kernel docs explicitly recommend copying struct definitions into userspace code that uses syscalls/ioctls directly. That way you can be sure of what version is in use, and you can name structs appropriately in order to avoid any conflicts. This can get messy if the kernel definitions vary by architecture, and then violating that recommendation becomes more reasonable, so I hope that's not the case.

On 1/12/26 4:26 PM, Johnson, Andrew N. via Tech-talk wrote:

This blog post might be helpful on how to modify Asyn to request non-standard baud rates on some Linux systems at least.

- Andrew

-- 

Complexity comes for free, Simplicity you have to work for.

On 1/12/26, 12:26 PM, "Tech-talk" <tech-talk-bounces at aps.anl.gov> wrote:

My quick google search suggests that it’s necessary to write a program to do this.

For python it recommends:

import serial

ser = serial.Serial('/dev/ttyS0', 28800)

print(ser.baudrate)

I tried this on Debian and it ran with no complaints.

On Jan 12, 2026, at 9:53 AM, Mark Rivers <rivers at cars.uchicago.edu> wrote:

Hi Eric,

I have an RHEL 9 system.  How do I set an arbitrary baud rate using termios2 from the shell?  When I use stty I get an error:

[epics@13idd ~]$ stty -F /dev/ttyUSB0 28800

stty: invalid argument ‘28800’

Try 'stty --help' for more information.

Thanks,

Mark

— 

Eric Norum

eric at norum.ca

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