rodw

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...

I know I'm trying to be lazy but why can't we install the PREEMPT_RT kernel from the Debian Bookworm Repositories? eg with: sudo apt install linux-image-rt-arm64. This appears to work but it does not boot into the new RT kernel. Downloaded the deb file and used sudo dpkg-i and it also failed to boot yet this command works if we install a RT kernel we built in the build environment Ran armbian-config and tried to install the kernel but alas its not displayed in the list. Why not? I can pull down Debian Bookworm for the Raspberry Pi from the Debian site and install preempt_rt this way. Why does Armbian make it so hard? Is there away to select the kernel to boot like we can do in grub on X86 PC's after installing it with apt? I know there is a high probability it might crash but at least I'd like to see that with my own eyes. It would be nice if we could install a real time kernel the same way we can do on other platforms. Help and ideas appreciated.

Oooops scratch this request. I took the darn thing home and it booted from the EMMC card! Sorry about that

Hi guys, My N2+ just arrived and I was able to install a Debian Bookworm (EDGE) image I built onto it (both to a SD card and an EMMC card) The selector switch is set to boot from MMC. Armbian fires up nice from the SD card but it does not boot from the EMMC. I can see the Drive with fdisk so I guess I need to copy the boot image onto it. (Its /dev/zram1) This is the first step towards building a PREEMPT_RT image so I was excited to see it sorta works! Any help or ideas would be appreciated.

Sorry, I got off track when you mentioned Xenomai as I had not considered that path, I'll wait until my armbian hardware arrives before asking further questions

Thanks for the welcome. The forum imposing a 1 post a day limit on me has not been condusive to our conversation! Hopefully that is in the past now! You've opened up a whole can of worms now! Maybe I chose the wrong platform with my N2! Going, I read up on all your links about Xenomai. Very interesting. Linuxcnc supports xenomai if the environment is detected at build time but I don't think V 4 has been used by anyone. One thing that might be helpful would be a reliable way to detect if xenomai was installed as its been pointed out the current method is rather crude. https://github.com/LinuxCNC/linuxcnc/blob/2e75b091a23e3312b9e57a88941714701f3709b8/src/rtapi/uspace_common.h#L361 I'm all ears if you could propose a better method that also detected Xenomai 4 Also, is network latency improved under xenomai? We have been experiencing network latency with realtek NICs on kernels 5.10 to 6.2 on Debian x86. Compiling the pristine upstream sources seems to help but its not a 100% cure. I don't think our RT needs are terribly onerous. We just need to ensure that latency is low enough that our servo-thread which usually fires every 1 millisecond does not run late. Regarding preempt_rt, we've never done anything other than to enable a fully preemptible kernel before building it. Anyway, thanks for the advice so far, if you have time to answer some of my questions it would be appreciated.

I know its been a couple of months since your post but I am interested in getting PREEMPT_RT running with Debian Bookworm on an Odroid N2. My interest is because PREEMPT_RT is a prerequisite for linuxcnc to run cnc machines. This requires strict timing to ensure the linuxcnc servo-thread fires on time every millisecond. Linuxcnc has recently been added to the Debian repositories and is available in Bookworm and Sid. I have recently built a Debian linux-image-rt .deb for the 6.1 PREEMPT_RT kernel which solved a few latency problems we were facing. What has become a bigger issue is network latency on the debian kernels from kernels 5.10-6.1 (bulleye and above). This is impacting on our RT ethernet devices as the thread timing is violated casusing the device and possibly a big machine to lock up! Today I think I was able to build the 6.2 RT kernel for the N2+ but until my N2+ hardware arrives of somebody tests my image stored on Google Drive, I won't know. The approach I took was to copy the RT patch as follows: wget https://mirrors.edge.kernel.org/pub/linux/kernel/projects/rt/6.2/patch-6.2-rc3-rt1.patch.gz gunzip patch-6.2-rc3-rt1.patch.gz then copy the unzipped patch to build/userpatches/kernel/meson64-edge This seemed to work as if I told the build system I wanted to change the kernel flags, it asked me to choose the premptible kernal method. So I decided to see if I could automate this more. so I copied build/config/kernel/linux-meson64-edge.config to userpatches and edited it to add CONFIG_PREEMPT_RT_FULL=y This file could be edited further to change any other flags Time will tell If I have got it right! I must say while it was a hard slog to work this out, I am impressed with the Armbian build system. I think all of this could be scripted. PS If you know anybody in the Debian RT team, please tell them their RT patch is broken!