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Ok you're telling me not to use a kernel that I have practical experience and have not had a single crash or anything similar. Neither have any users reported any crashes. I think an uptime of 39 days and being able to start Linuxcnc at anytime during that period with no crashes, latency errors or any other such issues proves to me that the kernel is solid and stable.
Before using it on the mill, I had been using to test some Mesa clones one based on a 7c81 and another more less based on the 7i92 design. I've also tested Ollie's riocore system, on the same 7c81 clone hardware early this year, before Oliie got his hands on a genuine Mesa 7c81 that he has made riocore formware for.
Could you point me to any papers, references or any such peer reviewed articles explaining why the 16k page kernel is broken by design.

So this time I will stand by my choices for the RPi5. Unless of course you can provide hard evidence as requested above.

Even this page says to config 2711 for RPi4 to RPi3 and 2712 for RPi5.
www.raspberrypi.com/documentation/computers/linux_kernel.html

A couple of things related to choosing a Kernel for Linuxcnc.

For the RPi4 you require options for the bcm2711 in the config.
For the RPi5 you require options for the bcm2712 in the config.

The change of the SoC broke a lot of stuff that broke GPIO stuff. What previously worked on the RPi4 failed on the RPi5. In the context of Linuxcnc this required a rewrite of the SPI driver for the RPi5.

For both SoCsmust be set. Otherwise we dont get the real time model required.

In the link you gave for the configs only the bcm_2711 rt config has that option set. The bcm_2712 config does not.

With regards to the kernel version the one on the image is uname -a
Linux raspberrypi 6.12.11 #1 SMP PREEMPT_RT Mon Jan 27 00:10:15 AEDT 2025 aarch64 GNU/Linux

This was built from the 6.12.y branch in January. Whilst not to up to date 6 months later it was in January and has proved to be stable. With regards to the kernel itself there have been no reports of crashing, except one user whilst using GMOCCAPY but this was traced to zram swap issue.

This is the one running my RPi5 on the mill, it's been up for 39 odd days with no issues. Having the power saving stuff turned off on the wifi has been constantly connected for those 39 days. Usually it powers down after some time.

unknown wrote:

I've tried looking for a RT_PREEMPT kernel in the repos, but could only find kernels that were configured for Real time not Preemptive real time (which is what Linuxcnc requires).

the packages are on archive.raspberrypi.org . you want linux-image-6.12.34+rpt-rpi-v8-rt, it works for both RPi 4 and 5. there's a meta package linux-image-rpi-v8-rt that depends on the latest version of the RT kernel, but it gives you auto-updates with apt, which is not necessarily a good idea (e.g. the currently-latest 6.12.47 is hanging my Pi5 sometimes).

it is a proper PREEMPT_RT kernel:

in order for bootloader to use it, you need to add kernel=kernel8_rt.img to /boot/firmware/config.txt.

the kernel configs themselves are here .

@f355

I've tried looking for a RT_PREEMPT kernel in the repos, but could only find kernels that were configured for Real time not Preemptive real time (which is what Linuxcnc requires).
Debian doesn't have any support for the RPi5 as it doesn't have enough upstream kernel support.
wiki.debian.org/RaspberryPiImages#Overview

and

raspi.debian.net/tested-images/

So to get a full RT_PREEMPT kernel the only solution it would seem is to roll our own. Which would not be a suitable solution for upgrading.

One solution maybe if Linuxcnc could host suitable kernels, but I really don't see the sense in a regular upgrade regarding the kernel in this situation. I'm still running the original kernel that was built whilst building the image in Jan 2025.

BTW running pi-gen builds a couple of flavours of images everything from lite to a fully image. Tho it does use a significant amount of disk space.