On 10/14/2017 11:24 PM, John Dammeyer wrote:
Hi Jon,
With respect to high speed encoder interface using the PRU on the Beagle I
may have misunderstood the comment from Charles from the second link below.
I'm thinking a 6000 RPM spindle with a 1000 line encoder detecting in
quadrature. That's tracking 24KHz which has a period of 41.667uS so I guess
the PRU can probably count that as long as it isn't doing to many other
things in that same 10uS interrupt.
Yes, there is certainly a speed limit using the PRU. You
have to calculate the count rate based on max spindle RPM
and count/rev of the encoder, and then make sure the PRU
will not miss any counts. You really have to do this with
ANY encoder counter, software or hardware, to make sure
counts are not lost.
Here's what I've found so far to a posting I did back in 2015.
https://groups.google.com/forum/#!searchin/machinekit/Beaglebone$20machineki
t$20lathe$20spindle%7Csort:relevance/machinekit/6klZrJH_2ZA/kDVr-6LgFgAJ
1. A reply from Jeff Pollard on which pins on the Xylotex 26 pin header to
use for the QEP along with instructions to not use the "A HOME/LIMIT" switch
on the DB-25 for homing and instead remove a filter capacitor so the index
pulse can be read. How to configure the Xylotex .ini file is not explained.
Past that the other link from 15JUN15:
https://groups.google.com/forum/#!searchin/machinekit/Beaglebone$20machineki
t$20lathe$20spindle%7Csort:relevance/machinekit/OvkMCwhhpjY/O0y1sl8y8OcJ
1. A comment from Charles which is what has led me to think the QEP for
spindle isn't possible on the Beagle yet. But that was more than 2 years
ago.
Yes, I think there has been a lot of progress since 2015. I
am quite sure that both PWM and encoders have been added to
the PRU code.
Jon
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