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sam
On 07/04/2017 05:22 PM, sam sokolik wrote:
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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