Jitter 40.000 and "unexpected realtime delay on task 0 with 57000" good enought?

Ok - then you might be at about as good as it's gonna get.

The only things I have found in some investigations I did in getting the best I could out of a couple of machines was:
[1] for some reason the Debian 10 iso gave me terrible results. I did a build using Mint 19.3 and install an RT kernel per this thrread:
forum.linuxcnc.org/9-installing-linuxcnc...nd-easy-installation
and i got a significant improvement. This may have been a quirk of my h/w.

[2] if you really want to get lower latency you might need to consider going to an earlier version of linux with an RTAI kernel. I'm not sure if there is a stable RTAI kernel on Debian 10.

There is of course nothing stopping you trying software stepping with that latency but its not an area I have played in so can't really comment on how things will go.

Cheers - J.

Thank you for all your comments. I have seen also there are mesa cards
store.mesanet.com/index.php?route=product/product&product_id=55
that might fit. If I understand everything correctly.
I need "only" a parallel port for my sherline stepper motor control box
Anyway, this is a new topic Befor this I will do some tests.

I'm in a similar situation as Roman. I have all the low power options turned off and I'm forcing a C state of 1 on boot.

I did not use the premade iso but I am on Debian 10 with preempt (confirmed with uname -v) and I get spikes in the servo thread of +- 200 us. I am on kernel 5.10 prempt for nic compatibility reasons but I would not think a newer kernel is the issue.

I don't claim to be a Debian expert so it's very possible there is a setting I missed or weird compatibility issues with my Odroid H2+ board. I was considering trying Mint and I think it's worth a shot after seeing your post.

I'm giving it a shot this weekend and will report back with results! Tommy if you are reading this thank you for the Mint 20 install guide!

I gave mint 20 a shot and it turns out my issue was not Debian, it was the 5.10 Kernel I had installed. After reverting to the 4.19 RT kernel and using a hardwire driver instead I got great latency results. Sorry, Roman probably not the easy answer you wanted.

I do find it can be a good idea to re-install stuff sometimes when you stuck. You might notice something you missed the first time around. The nice thing about LinuxCNC is you simply drop in your config files and it just works! I would recommend mint 19 over 20 if you do try again. 20 has some compatibility problems with QTvcp screens. Probably a way to get it working but when reverting is so easy I took that route.


Here's the install guide Tommy made if you want to give it a shot!
forum.linuxcnc.org/9-installing-linuxcnc...nd-easy-installation

Hello, sorry for my late reply, I also tried Mint 19 but this gave jitter values beyond good and evil. I think there is a driver issue with my system or something like this. Installation works fine, Mint had internet access during installation and seems to run fine, not LinuxCNC. Thanks for the RTAI tip, I will try this also and will reply. Best Regards Roman

I just tested the RTAI version and get much better results

Max Jitter 26.000
Under Load (Youtube HD Video, OpenGL Tools) I can push it to 33.000

It is not the best, but it is cheap (< 100 EUR) and current hardware. I am very glad about these results.

Thank you all for your help!!!

--
Update, after an hour of idling, Max Jitter jumped to 35.000

--
Update sherline mill runs fine with sherline driver box and 35.000 Max Jitter and half steps.
I have seen that the factory sherline computer runs with 50.000 Max Jitter in the settings.
Motors sounds nice, like normal steppers. Do not hear something worrying. 1 mm Leadscrew
and max speed is 12 mm/s, this is not slow on such a tiny machine.