This phenomena is known as PRU pin hunting and a result of the internal PRU stepper feedback loop being too "tight" (so the DIR pin toggles all the time). You can fix it by adding a PID loop before the stepper and adding a minimum threshold. Just search for PRU pin hunting in the mailing list.
Another solution would be to adapt the PRU HAL driver code. However, the PID loop has the additional advantage that it smoothes out RT jitter. The solution is also present in the Machinekit fdm Python libraries: https://github.com/machinekit/machinekit/blob/master/lib/python/fdm/config/base.py#L61-L75 [email protected] writes: > Hello Nick, > If i am correct this is some form of "hunting" mode which is being done by > the feedback loop in the PRU. I have seen the same behavior on our > machines, but I have no clue what this actually does internally in > machinekit. > > Op woensdag 10 mei 2017 11:14:45 UTC+2 schreef Nick Collier: >> >> I am running Machinekit on a BBB. >> >> When tasting the physical step and direction output pins with an >> oscilloscope, I noticed that there are various rectangle/pulse type waves >> on the direction pins when the respective axis are not moving. Is this >> normal? >> >> As soon I make the axis move, the direction pin goes to either high or low >> depending on the direction. >> >> When the axis are moving, everything looks fine. But I would expect no >> signal when there is no movement. The step outputs produce no signal when >> there is no movement, so I guess the signal from the direction outputs are >> not going to do any harm. >> >> -- Alexander -- website: http://www.machinekit.io blog: http://blog.machinekit.io github: https://github.com/machinekit --- You received this message because you are subscribed to the Google Groups "Machinekit" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. Visit this group at https://groups.google.com/group/machinekit. For more options, visit https://groups.google.com/d/optout.
