Re: [Emc-users] closing the loop in linuxcnc with a 7i76 mesa card and step direction control

[Phill Carter]

> On 6 Apr 2020, at 1:34 pm, Jon Elson <el...@pico-systems.com> wrote:
> 
> On 04/05/2020 08:51 PM, Phill Carter wrote:
>> Sorry to jump in here but I have a quick question for Jon, do the Pico cards 
>> require a base thread or do they use only a servo thread. I guess what I am 
>> asking is are they OK on a PREEMPT RT machine with not so good latency or do 
>> they require RTAI with a "good" latency.
> No base thread is required.  For the Universal Stepper Controller, the 
> encoder or step position is read at a nominal 1 ms servo thread interval, PID 
> is computed and a new velocity (step rate) is sent out.  The digital I/O is 
> also processed at the 1 ms rate.
> 
> Still, since the software is commanding the sampling of position, decent 
> latency is required.  RTAI is NOT required.  Preempt-RT now has quite good 
> latency on many motherboards.  You do want the jitter to be less than, say, 
> 5% of the period.  So, for a 1 ms thread, 50 us would be the worst you'd want 
> to see, and something down around 10 - 20 us jitter would be better.

Thanks Jon.



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