MESA 7i76e Stepgen Frequency

Hi everyone,
I've been working with a MESA 7i76e for a while now and I'm actually quite experienced (or so I would say ).

Now I am expanding my machine with an A-axis. I would like to drive the motor with 100kHz. At 50 kHz (MAX_VELOCITY=625) everything still runs well. But when I go to 100kHz (MAX_VELOCITY=1250), I get a position error that I can't explain. The MESA card should not have any problems here yet.

Does anyone want to help? Maybe it sounds familiar to someone.

Thanks in advance

It may be a setup error of some kind (7I76E stepgens are capable of generating
step rates of more than 10 MHz)

You may need to plot the following error + velocity with halscope to debug this


This might be an issue:

setp pid.a.maxerror 0.012700
(= .0127 degree)

That's only ~1/100000 of dynamic range for the A axis PID loop so might be less
than the LinuxCNC/7I76E clock differences.

Just tried setting the maxerror to 100 and got the same error.

The first professional screenshot shows the behavior at 50kHz, the second at 100kHz. As if the Stepgen or PID suddenly stops at a certain frequency.

A screenshot is smaller and much more legible than a photo

You're right, of course. I couldn't have done any better at that moment.

I would widen the following error limits to see what's happening
(and scale the following error so that the limit (0.5) is on screen)


It might be that you are dropping packets (timing out) which
can cause a following error of velocity/servo_thread_period

I have increased the following error and now it works. The MESA card must have made too many steps between two queries and thus triggered a following error. A bit confusing, as I would have expected the error message "Following Error" and not "Position Error".
Anyway, thanks a lot.

There was a following error for some reason, my guess is that you have dropped packets

You might need to raise the servo thread period

You can check this by looking at the "packet-error-total pin"

Packet-error-total? Can not find it. Only this pins see image attached.