6i25 custom firmware and weird latency

I'll see if I can duplicate this here. Still sounds like bad hardware (Either 6I25 or PC)

Actually it is not related to PWMBDirPin. I just had pwmgen.output-type 2, so it didn't output anything until B pin was present. If I set output-type to 1 or value to -0.5, the latency problem starts as soon as I have a PWM output pin.

Seems like it may be some kind of EMI problem caused by the PWM output. Weird though, considering I don't even have any cables connected.

Definite correlation with PWM frequency, if I raise it from 40 kHz to the 390 kHz maximum, the latency effects start occurring multiple times per second.

I guess I'll try another PC next, and maybe try to scope the power lines or something. Though it feels weird that toggling an IO pin that is just connected to a few centimeters of PCB trace and has slew rate set to slow would cause so much EMI.

A shorted GPIO might cause that kind of an issue. You might verify that all GPIO
are at 5V when linuxCNC is not running

Thanks, I'll check that also. Though the problem appears to occur no matter which GPIO I use for the PWM so it's probably not that. The PWM output also appears to work correctly.

I'll report back next week on my findings

Looks like it was a bad PC after all.

Trying the other PCIe slots on the motherboard, it crashed the whole PC immediately.
I measured the +12V and +3.3V voltages on the PCIe connector, but they both looked fine.
Probably some poor EMI-sensitive design on the motherboard.

Anyway, I got another PC and now it works fine with the same configurations.
Thanks for the troubleshooting help!

(For future reference, the bad PC was Fujitsu Esprimo E500 E85+)