Raspberry pi rt preempt

Runtime 🇬🇧
hcvoort
2022-04-18
2023-12-25

  • hcvoort - 2022-04-18

    Hi,

    A couple of years ago I used the Pi as a soft PLC in which you could apply an rt-preempt patch to the kernel to reduce jitter. I remember that Edwin also made a short post on how to do this. Is there still a quick way to patch a kernel for a Raspi 3B? Or do I really have to build a kernel?

    Thanks!

    Carsten

     

  • mondinmr

    mondinmr - 2022-04-18

    You could use Debian image.
    In Debian repo you can find RT PREEMPT precompiled path.
    Tuning kernel cmdline using CPU pinning and using a fixed pinning on codesys task make possible a jitter <30us on a PI4.

     

    • hcvoort - 2022-04-18

      Thanks for your comment. Do you have link for the debian repo?

       

  • mondinmr

    mondinmr - 2022-04-18
     

    • hcvoort - 2022-04-18

      Thanks. I went through it but only saw standard builds (tested). Could you point me to the precompiled images with preempt-rt patch?

       

      • mondinmr

        mondinmr - 2022-04-19

        I searched again!

        RPI 2 is supported in debian with
        linux-image-rt-armmp in 32 bits arch

        RPI 3 I cannot find info

        RPI 4 apparently only in 64 bits linux-image-rt-arm64 (Tested by me in debian daily build) and CODESYS for arm at 64 bits

         

        Last edit: mondinmr 2022-04-19

  • mondinmr

    mondinmr - 2022-04-19

    I just mounted a PI2 image:

    $ unxz 20220121_raspi_2_bullseye.img.xz
$ sudo losetup -Pf 20220121_raspi_2_bullseye.img
$ sudo mount /dev/loop24p2 /mnt
$ cd /mnt/etc/apt
$ cat sources.list

deb http://deb.debian.org/debian bullseye main contrib non-free
deb http://security.debian.org/debian-security bullseye-security main contrib non-free
# Backports are _not_ enabled by default.
# Enable them by uncommenting the following line:
# deb http://deb.debian.org/debian bullseye-backports main contrib non-free

    Enable those repo in raspbian than:

    $ sudo apt-get update
$ sudo apt-get install linux-image-rt

    NEVER DO apt-get upgrade!!!!
    Remove repos before!!!

    In a Raspberry PI 4 64bit it worked for me, but now I'm switching to a my distro built with YOCTO.

     

  • oe2swm - 2023-12-25

    Hello,

    I tried very hard to get Raspberry working with RT PREEMPT Kernel,
    But still i cannot get it working. Is there someone who can provide a Image for Raspberry 3b or 4(4gb)

    Thanks a lot!

     

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