Sorry guys, I did not get notifications on this thread. Thanks for all the responses.
Back to my quote here:
There is a simple method to get preempt_rt on a raspberry pi running Debian which I have documented in the Linuxcnc docs here
http://linuxcnc.org/docs/2.9/html/getting-started/getting-linuxcnc.html#_install_debian_bookworm_on_a_raspberry_pi
No code or patches required!
I have not tried it against the standard Pi image but I think it would still work as the Pi now uses Debian under the hood.
In any case, the Pi's chroot build environment does let you patch the kernel quite simply. Armbian's looked like it should allow that too but it failed for me after applying the preempt-rt patches
I have done it in other ways with help from one of your guys, bit there was a regression that affected latency,
If there was a simple way to do the same on Armbian I would have included it in those docs to spread the word.
Note my post here was driven from a certain amount of frustration while I was writing the docs I linked to.
Anyway, we'll get over the line eventually...