I have been playing with linuxcnc for a long time... It has come a long
way.
Currently the RTAI folks seem to have issues developing.
Now there is RT_Preempt. Couple cool things.. It has been migrated to
the linux foundation. This means a lot eyes on it. It is also pretty
easy to build. I have done it quite a few times now. My experience is
that the out of the box rt_preemt has ok realtime performance.
Anywhere from 20 to 100us latency. Perfect for external interface cards
(mesa, pico and such). I have a computer that has decent enough
rt-preempt performance that it is running 50us base thread. (small emco
lathe - 100 line encoder for threading) I have been running this for
quite a while this way with no issues.
Why am I rambling...
Well - I have been playing with debian stretch and 4.9.0-3-rt kernel.
I booted our matsuura (j1900 quad core) which with no tweeking has aprox
100us latency. (it has been running mesa ethernet cards with rt_preempt
- no issues) Next I booted it with some kernel line tweaks. (checking
the hardware - processors 0,1 and 2,3 share cache. So I added
isolcpus=2,3 idle=poll
The latency on this system was phenomenal. It has been running for
hours now and still <6us
these numbers are as good or better than rtai. Could we, with some
tweaks, use rt_preempt for printer port configs and forget about rtai
for now? I have more computer hardware I can test - but this is pretty
awesome.
Good video explaining realtime https://www.youtube.com/watch?v=BKkX9WASfpI
Rt-preempt even runs decently on my laptop. I have actually run test
and real machines with it. (don't mute the speakers though... causes
huge spikes)
sam
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