tune stepper function

The white trace is basically the stepgen velocity command
( fed forward via the PIDs FF1 = 1.00 parameter )

But if you have the stepgen's steplen and stepspace
settings too long for the commanded rate, the stepgen will be
unable to follow.

Is that behaviour linuxcnc specific?
I haven't heard similar restrictions before.

Any stepgen that does not violate minimum step pulse high and low timings will have these
limitations. That is if I have a step length of 2.5 usec and a step space of 2.5 usec, the
minimum total period is 5 usec or 200 KHz. If I command a higher speed, the step generator
will lag behind. In addition there needs to be some control overhead so the actual maximum speed
will need to be somewhat lower than 200K steps per second.

The timing limitations are clear. Was a silly mistake at beginning of this thread.

But the control overhead - is that linuxcnc specific?
Never heard that restriction before.

Its not LinuxCNC specific but may be more exposed in LinuxCNC

Ah, I see. It's because linuxcnc is able to do closed loop at application level.
Simpler controller apps like mach3/4 are not able on that control level, so they simply command the amount of steps - and thus don't know/care about the control overhead.
Right?
That's why linuxcnc uses a pid-loop with steppers.