Lars, I have been following the RTPREEMPT scene for quite a while now. The people at SSAB (Proview) run their plants on it, so they have a vested interest and they are very clued up on it (their software is much more polished than LCNC by the way, mainly because they get paid to keep it that way off course) In any case, They found that in their tests "a looptime of 1 msec is no problem". I take it that this is with a purposely selected motherboard / cpu.
This is very good off course. The lowest figure I have heard in the CNC world is 500Usec. But that I would consider nonsense for the market LCNC is operating in. 5 millisecs servo looptime is ample in almost all cases. My own work on the subject sugests that all this is only possible with a well tuned computer. If the tuning is not perfect you might see some unexplained latencies happening at odd times like the middle of the night. this would make PREEMPT_RT useless for steppers, even if we do find a board with low enough latencies. (And they exist already, there is no doubt about that) So this is how I come to the conclusion that there is a lot of merit in keeping the micro-kernel / interrupt pipe with linux on top alive. It will be a right royal fest of failing installations when all of a sudden LCNC would change to PREEMPT_RT only, nobody wants that. At the same time for industrial installations with Sercos or Profibus or Ethercat servo loops PREEMPT_RT will ease the development cycle since a lot of the drivers that are around already will intergrate easier. cheers, j. On Thu, May 17, 2012 at 12:25 AM, Lars Segerlund <lars.segerl...@gmail.com>wrote: > A quick question, > > I would like to ask what speed you 'guess' / estimate the stepper > lovers need ? ... and with speed I mean max allowable latency. > Perhaps I could also ask about the speed for the loop ? > > On a well tuned x86 system, a 100kHz loop speed for the steppers > should be easily obtainable, and 250+ possible, if I'm not totally > wrong. > > / regards, Lars Segerlund. > > 2012/5/16 Jan de Kruyf <jan.de.kr...@gmail.com>: > > Hallo, > > Back from a week bundu-bashing. > > I would say from my side that I see a fair amount of work in the > PREEMPT_RT > > patches still needs doing. > > Besides the point that the stepper lovers will allways want the speed of > > RTAI / XENOMAI. > > > > The ARM problem (besides what you mention below) leads me to believe that > > some serious work > > needs doing on the Xenomai patch to bring it up to scratch. > > But for my own reasons I am devoting what little time I have at the > moment > > to PREEMPT_RT. > > > > Hope this helps the discussion. > > > > > > j. > > > > > > > > > > > > On Fri, May 11, 2012 at 6:10 PM, Kent A. Reed <kentallanr...@gmail.com > >wrote: > > > >> Gentle persons: > >> > >> The recent email discussions about ARM-based cpus on the one hand and > >> about progress with the PREEMPT_RT patch on the other got me to > >> wondering about RTAI and where it is going. > >> > >> I see that two test versions of rtai-3.9 were posted in quick succession > >> in January/February of this year. > >> > >> As best I can interpret the Changelog, version 3.9 is supposed to > >> support Linux kernels up to 2.6.38 although the second test release > >> appears due in part to some failure of the first test release to achieve > >> this goal fully. (The only mention of ARM in the Changelog dates from > >> 2009 so I won't say any more in this message about ARM.) > >> > >> The last Ubuntu long-term-support release was Ubuntu 10.04.3LTS, aka > >> Lucid Lynx, based on kernel 2.6.32. It reaches its official end of life > >> in 11 months. > >> > >> As of a few weeks ago, the current Ubuntu long-term support release is > >> Ubuntu 12.04LTS, aka Precise Pangolin, based on kernel 3.2.14. > >> > >> I feel no pressure to rush to new Linux distributions since I keep my > >> desktop usage separate from my machine-control usage. Even if I did, I'm > >> personally comfortable with mixing-and-matching kernels and > distributions. > >> > >> However, it would appear from other email traffic that a number of > >> LinuxCNC users want their latest and greatest hardware supported by the > >> latest and greatest distribution releases so they can do everything on > >> one computer. > >> > >> Given the stated commitment of the LinuxCNC developers to LTS releases > >> of Ubuntu, the age of 10.04LTS, and the apparent lack of any RTAI > >> roadmap indicating when kernel 3.+ will be supported, has a 'position' > >> been formulated on the disconnect that exists today and likely will > >> exist for some time to come? > >> > >> It would be great if other work---PREEMPT_RT, Xenomai, etc---end up > >> making this a moot point but I was taught (my first employer paid for it > >> and I have a yellowing certificate suitable for hanging to prove it!) > >> that good project management does not include praying for a miracle :-) > >> > >> I'm just saying.... > >> > >> Regards, > >> Kent > >> > >> > >> > >> > ------------------------------------------------------------------------------ > >> Live Security Virtual Conference > >> Exclusive live event will cover all the ways today's security and > >> threat landscape has changed and how IT managers can respond. > Discussions > >> will include endpoint security, mobile security and the latest in > malware > >> threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ > >> _______________________________________________ > >> Emc-developers mailing list > >> Emc-developers@lists.sourceforge.net > >> https://lists.sourceforge.net/lists/listinfo/emc-developers > >> > > > ------------------------------------------------------------------------------ > > Live Security Virtual Conference > > Exclusive live event will cover all the ways today's security and > > threat landscape has changed and how IT managers can respond. Discussions > > will include endpoint security, mobile security and the latest in malware > > threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ > > _______________________________________________ > > Emc-developers mailing list > > Emc-developers@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-developers > > > ------------------------------------------------------------------------------ > Live Security Virtual Conference > Exclusive live event will cover all the ways today's security and > threat landscape has changed and how IT managers can respond. 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