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.
Jon
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