RockPro64

What distro did you use for your build? Those are some great looking latency tests. I'm looking to put a Mesa PCIE card into the Rockpro64 slot and make it a full-fledged controller, so this is very promising.

with the fpga card or a eth you do not need latency at all
it is internal hardware steps that are generated
no software timing involved

Not completely true, you still need good enough latency to run the servo-thread, so Linuxcnc can do the motion planning and io sampling properly.

At the moment, I am running Stretch 9.8 with linux 5.0.7-rt5.

pl7i92 wrote: with the fpga card or a eth you do not need latency at all
it is internal hardware steps that are generated
no software timing involved

Yeah that's not quite true. Hm2 will generate steps and count encoders in FPGA fabric but the CPU still has to respond to the the stepgens or update from the encoders quickly. It's a hell of a band-aid to not great latencies but single ended GPIO isn't effected at all so if you had to read or write to I/O with something other than an encoder or stepgen it doesn't help at all.

Then again encoders and stepgens are probably the worst 2 things you can have to handle with software so it is much better for these.