Jon: when I started working in the CNC field we had 20msec loops and they worked(cutting steel) from pure fanciness we would upgrade to 10msec, and with a well tuned servo drive you could feel the distinct steps of the DAC while accelerating. Afterwards I learned to tune a servo by holding the table feeling for those steps. Off course on a small high speed machine the picture changes considerably. But at the same time I guess that the problem you are describing might be caused in the digital speed servoloop, by the jitter of the CPU board, and / or a poor setup of the positioning loop.
In any case: from the grumbles in this thread we might perhaps deduct that there is money in a good micro stepping board, that takes position or speed input every msec or so; for the stepper people. Lars: What would you say? Gene: I think that you are perfectly illustrating the point that the personal computer designers let chaos reign in the time domain to get the job done quickly ;) It has not changed a bit. A properly set up PREEMPT kernel is slower at ordinary computer work. Just build a kernel on your machine, once with RT enabled and once without it. Its just our improper use of PC's that has need for all these time constraints. Kent: this is not the P(sycho) word causing it, it is the F(inance) word. Here we get a free ride on the back of poular culture and you are still complaining :) j. On Fri, May 18, 2012 at 4:52 AM, gene heskett <ghesk...@wdtv.com> wrote: > On Thursday, May 17, 2012 10:33:42 PM Kent A. Reed did opine: > > > On 5/17/2012 4:18 PM, gene heskett wrote: > > > On Thursday, May 17, 2012 03:56:00 PM andy pugh did opine: > > >> On 17 May 2012 14:33, Jan de Kruyf<jan.de.kr...@gmail.com> wrote: > > >>> Andy > > >>> Until we do proper tests: see the OSADL numbers for the various > > >>> board / cpu setups > > >> > > >> The Core2Duo system they have looks like it would software-step > > >> perfectly adequately > > >> https://www.osadl.org/Latency-plot-of-system-in-rack-1-slot.qa-latenc > > >> ypl ot-r1s2.0.html > > >> > > >> Some of the other systems look decidedly poor, which is a shame > > >> because what LinuxCNC really needs is a reliable works-on-any-system > > >> RT layer. > > > > > > Looking at some of the other results, I am amazed at the generally > > > poor performance of the ARM's in general. > > > > > > 25 years ago, looking for the reason I could literally spend days > > > trying to download some of the early programs for the TRS-80 Color > > > Computer. which at that point had a motorola MC68A09EP in it for a > > > cpu, running at .889 mhz. <...> > > > > > > Then that once a minute ghost trace disappeared and I could download > > > major sized bits of programming without rzsz ever detecting or > > > needing to correct an error. > > > > > > The point being, that if a processor that runs at .889 mhz can do it > > > in 15 microseconds, why can't a modern cpu running at 2000 times the > > > 6809's speed, do it in 7.5 nanoseconds? Somethings wrong with this > > > picture. > > > > > > Cheers, Gene > > > > Oh, please, stop before you get me started reminiscing about Z80 cards > > stuck into my homebrew Apple II :-) Seeing rzsz in print was a bit of a > > shock. > > Sorry 'bout that. :) In fact, the several hundred people who still have > working coco's, including me, (we have a mailing list with about this lists > traffic level) are using the rzsz package that I compiled on the well > equipt coco3 in the basement. But I had to fix the compiler, then threw > away some of Chuck Foresburgs code, switching to a table lookup method of > checking crc's that was about 20x faster than Chucks code. Between that > and one other little tweek I used dozens of times in the final version of > what I built (version 3.36) I raised the throughput on the coco from just > over 400 cps, to about 740 cps. > > Those folks are having the 23rd annual "Last CoCo Fest" in Elgin IL this > weekend. And if they get their expenses back, they'll have a 24th Last > CoCo Fest next year. One of the venders is bringing a socket adaptor to > fit the atari 8 bitters that puts a 6809 in an atari, running os9 no less. > > > I seem to remember posting a rant to the emc-users list a year or more > > ago lamenting this "progress" toward cpus and graphics chips optimized > > for multimedia and/or games to the exclusion of everything else. I > > suspect the line managers are like a boss I once had, always ready to > > jump to the next bandwagon and absolutely incapable of admitting they've > > given something up in the process. It's hard to argue with them raking > > in the big bucks. > > > > A friend of mine clued me into a psychological/sociological phenomenon > > known as "shifting baseline." With a little massaging, I think it could > > be used to explain our current circumstance. > > > Probably, Kent. But I have other things to do. Someone has likely even > invented a word for it. ;) > > > 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 > > > Cheers, Gene > -- > "There are four boxes to be used in defense of liberty: > soap, ballot, jury, and ammo. Please use in that order." > -Ed Howdershelt (Author) > My web page: <http://coyoteden.dyndns-free.com:85/gene> > A good supervisor can step on your toes without messing up your shine. > > > ------------------------------------------------------------------------------ > 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
