Emco PC Turn 55 retrofit

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08 Feb 2021 19:15 #198051 by The Feral Engineer

Those issues are not likely to be latency related, even 100s of usec of latency
have negligible effect on the step generation and the maximum step rate is
complete unrelated to latency with Mesa cards.

If you have poor latency (but good enough to avoid real time errors)
You do need to have the DPLL setup and enabled to be able to generate
clean step signals.


How would I check this?

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09 Feb 2021 23:24 #198220 by PCW
Replied by PCW on topic Emco PC Turn 55 retrofit

Those issues are not likely to be latency related, even 100s of usec of latency
have negligible effect on the step generation and the maximum step rate is
complete unrelated to latency with Mesa cards.

If you have poor latency (but good enough to avoid real time errors)
You do need to have the DPLL setup and enabled to be able to generate
clean step signals.


How would I check this?


You should have something like this in your hal file:

# latch 50 usec before nominal read time:
setp hm2_7i76e.0.dpll.01.timer-us -50   # set timer 1 to 50 usec before read
setp hm2_7i76e.0.stepgen.timer-number 1 # use timer 1 as sample time reference for all stepgens 

Note if the latency is really bad you may have to increase the time to 100 usec or so
because of baseline drift.
The following user(s) said Thank You: The Feral Engineer

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09 Feb 2021 23:43 - 09 Feb 2021 23:43 #198223 by The Feral Engineer
Thanks Peter

I'll check it out when I get back on the pi. I reconnected my laptop for my turret prove out. Pi is my endgame, but it's a pain in the rear with the keyboard and monitor sitting on top of the machine.
Last edit: 09 Feb 2021 23:43 by The Feral Engineer.

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18 Feb 2021 07:40 #199221 by The Feral Engineer
I set the pi back up, have it hooked to an asus touch screen and I've been able to do some playing. I did an isolcpus = 2,3 and I have a better servo-thread jitter result than not having any isolcpus (130000 vs 280000 if I load chromium and start playing youtube videos). I have my servo timing set to 140000 in my ini file and as long as I don't use wifi with the machine enabled, it seems to run pretty reliably. If I try to surf the web and jog the machine, it isn't happy about it at all, which is fine.

I haven't tried the DPLL thing yet, I actually came on here to read up on how to do it and figured I'd give an update on it.

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