Fast PWM strange behaviour

[stebhend]

Dear CNCdrive

I have a Stepcraft M700 over a UC400ETH.
Direct connection of RJ45 from Computer to Controller.
The versions are:
Software 1.2111
Firmware 1.480
Hardware 1.0000
API 2.1790
Screenset V1.2

The milling works like a charm.

Now i bought a Neje Laser Module.
Over Laserengrave it engraves perfect.
But i have different jobs, where i need to engrave and cut in the same Process.
I know, there would be workarounds to handle this, but it’s not very convenient and precise.
Also the lack of saving is not very productive.

So i bought a license for Lightburn and load via Lightburnloader.
That way i could produce a file with one programm.
When i engrave with 0.2mm intervall everything works most of the time, seldom dropouts.
The engraving looks not very nice, so i wanted to go down.
Then the Laser didn’t work properly.

So i took a scope to check where the error is.
As soon as i go under 0.2 the PWM (measured directly at the D-Sub of the Stepcraft Pin 2 - Pin 7) has dropouts.
When i go down with the look ahead lines count to 100, the PWM comes out perfect. With 101 are dropouts.
It doesen’t matter wich speed, and i can slow down the machine with jogwheel to 5% and still dropouts.
This makes me assume, that there is no problem with the Computer.

That would be the solution to go to 100 look ahead lines count, but under 150 it stutters every 7-8mm.

My Computer is a Dell Optiplex 3080, Intel Core i5-10500T with 2.3Ghz and 8GB Ram.
Yesterday i Upgraded from Windows 10 to 11 (64Bit) and no Change at all.

Comm buffer size i changed from 0.1 to 0.5 to 0.05. No change.
Kernel frequency 100 50 and 25kHz tested.
The file is straightforward lines.
It’s the Grayscale Cube.