Installing Linuxcnc and Debian Bookworm on problematic hardware (eg. Realtek NIC

Running Debian Bookworm or Bullseye with some hardware (notably PC’s with Realtek network interfaces) has proved problematic as a new type of latency emerged. Network Latency between the PC and motion hardware. If the network becomes too slow, there is insufficient time for Linuxcnc to get things done and mesa network hardware shuts down after issuing an error finishing read. Ethercat drives with slaves disappearing intermittently are also likely to be caused by this issue. Previously stable hardware has become problematic due to this problem.The issue occurs on some hardware with any version of debian from kernel 5.10 (Bullseye) and above through to the latest kernel 6.1.

These are the versions of Debian to support modern hardware. Installing Bookworm is an attractive method to get Linuxcnc installed as it is deployed as a Debian package on this Debian version.

There are two issues involved here.
1. A problematic PREEMPT_RT realtime kernel deployed with Debian that adds to network latency.
2. A confusing set of realtek network drivers in Debian and a mismatch between the default driver and the hardware.
Resolving the first issue used to require compiling the Linux kernel but now a prebuilt .deb of the kernel and the headers. These have been built using the pristine source of the 6.1 kernel from kernel.org so it's not affected by Debian’s kernel patches.

Realtek drivers.
Debian has 3 Realtek drivers in Debian:
The default r8169 driver used with all realtek hardware by default
The r8168-dkms driver that covers a large range of NIC’s (ref: packages.debian.org/bookworm/r8168-dkms)
The r8125-dkms driver that supports the new 2.5 gb NIC’s found on the Odroid H2+/H3/H3+ pcs and an increasing number of other PC’s (ref: packages.debian.org/bookworm/r8125-dkms)

dkms drivers are compiled from source on installation and need the linux-headers. These contain all the C header files to allow building software against the kernel. The default r8169 has no installable driver. To reinstall it, you need to purge any dkms drivers you have installed (eg sudo apt purge r81XX-dkms)

So it sounds pretty simple right? We just need to install our custom kernel which is likely to be cdimage.debian.org/cdimage/unofficial/no...mware/weekly-builds/ for any PC that does not have Realtek drivers) and install the correct driver for a Realtek NIC.

Note that it's not necessary to reinstall Debian if you are afflicted with this problem, you can just update to our custom 6.1 kernel and its headers on the link below and optionally install the correct Realtek driver.

The next post will work through a step by step approach on how to install bookworm that contains the linuxcnc packages.

Start by downloading the Bookworm non-free version from the weekly builds here
cdimage.debian.org/cdimage/unofficial/no...mware/weekly-builds/
Usually you will want the amd64 version and I usually select the cd version making sure that the PC is connected to a wired network during installation. Burn it to a USB stick and install it in the usual way but be sure you select the XFCE gui. This is mandatory to ensure xorg elements linuxcnc needs exist.



Then we’ll meet up on the next post and get on with it.

Lets start:download linux-headers and linux-image from here
drive.google.com/drive/folders/10uwGg5Rv...LtQ8BZhM3At_gODk16naNote that pressing (tab) above lets linux autocomplete the line for you to save typing
Make the new 6.1 kernel the default. Eg move to the first entry.
reboot and check our kernel loadedand save the name of the NIC you will use for your mesa card (enp2s0 for us)
Check the device specsNote the driver is r8169 but the hardware is rtl8168e
So debian is using the wrong driver. install the correct driver
First check that we are not going to look in CD or DVD drives for softwareComment out any lines beginning with CD or DVD with a #
Save and:Once rebooted, open a terminal and:note driver is now correctly listed as r8168

So Our job is done! time to configure the wifi at top right and set up the NIC interface for Mesa
But first install linuxcncAssuming you have already configured the mesa card to be add this text at the endIf not you'll need to set the ip to 192.168.1.1 above,
then use mesaflash to save the 10.10.10.10 ip address to the mesa card first,
then edit the file whats above again so it can be found again.

Restart the network
Open a mesa based configuration (or use pncconf to create one)
Let it run for a while. While it is running,
in another window, check the network latency by reviewing the TMAX settings on your card
Note these values are in timer ticks, not nanoseconds.

If something goes wrong and you loose your network interface, reboot into the earlier 6.0 kernel and
the interface should be there. remove it.reboot into our custom kernel and it should still be there. Re install the driver and reboot the PC to enabl eit.

Follow the tweaks on JT's web site to enable auto login etc
gnipsel.com/linuxcnc/debian-11-fix.html


Also there is a recent issue with Bullseye and Bookworm where it refuses to run linuxcnc on the default gnome desktop which uses wayland. I generally only install the XFCE graphical environment as its a XORG environment and it works perfectly

This can be solved on wayland by adding an environment variable before running linuxcncThis may not stick on a reboot. you can add it to your .profile file as follows so its loaded when you log in.
add the export statement to the end of the file and save and exit Ctrl-O, Ctrl-X
 

So with that behind you, you should not experience error finidshing read with your mesa card and your ethercat drives should not go AWOL.

Mods might like to sticky  this.

Rod,

Thanks for the write-up.  Explains some of the issues I've had with my H2+.

I'm starting a fresh install and, as usual, running in to problems following your process above.  If you don't mind assisting, would you like me to start a new thread or post up here?

thx,
Ralph

I'm happy for you to help
By all means post up here as it might help others.
I've been spending a fair bit of time working on a Debian ISO Installer.
Last night I got it to install Debian with my custom kernel from an ISO. Unfortunately it installed it under Bullseye instead of Bookworm so it could not then install Linuxcnc from the Debian repos.

I'm hoping I'll get that fixed in the next day or so. I'm sure I just missed a setting. Using an ISO will solve a lot of problems
Worst case, we could install Linuxcnc from pre-built debs.

okdokey...

PC is an Odroid H2+ with the rtl8125 nic.
First hiccup was during installation of Bookworm - additional firmware required despite using the non-free network install iso.

Found the firmware.zip buried somewhere on the Debian site and added it to a USB during install and got past that hurdle.

Your 6.1 rt kernel installed ok.

Next issue: it appears I'm unable to install the r8125-dkms driver.

error during attempted driver installation



LCNC is installed and axis is working.  Haven't bothered to move on the mesaflash yet.

Any ideas?

On the Odroid forum, there is a note that the realtek driver vs the Debian driver is up to 25-30% faster.
I have installed the Realtek Driver on an H2+ but it was back on Buster before it was released in Kernel 5.9. I just had to install from a DVD iso and insert a usb stick containng the realtek source and it worked.

You might need to look at the kernel versions supported by the realtek driver and fall back to a supported kernel version.

You could also try installing the r8125-dkms before installing the kernel. It will rebuild the driver when the kernel is installed via dkms...
Matter of fact one of my pcs righted itself this way....

Hope that helps.

PS I have an Odroid H2+ happilly running Bullseye and Ethercat. I'm not going to touch it!

Oops, the Realtek source says its good to kernel 5.19
www.realtek.com/en/component/zoo/categor...pci-express-software

Earlier versions of bullseye ran 5.15, 5.17 and 5.19.
 

So...  survey says to grease Bookworm, load Bullseye, and get a 5.19 RT kernel?