On Tuesday 03 September 2013 04:32:26 Michael Haberler did opine: > Am 03.09.2013 um 05:41 schrieb Gene Heskett <[email protected]>: > > On Monday 02 September 2013 23:18:36 Jon Elson did opine: > >> I'm not sure theis is the right method to bring this up, but... > >> I have had some discussions with Michael Haberler about having > >> the capability for making HAL threads triggerable via an > >> external interrupt. Apparently, there was a partial capability > >> in an early version of rtapi, but it was removed, possibly because > >> it didn't work. > >> > >> Anyway, my line of interface boards have always had the capability > >> of sending an interrupt pulse through the parallel port on a regular > >> interval of 1, 2 5 or 10 KHz. These boards also sample the encoder > >> position in hardware at that time, and exchange signals on the > >> parallel port bus so all boards sample within 1 us. Since this > >> was not supported in HAL/rtapi, we have not been using this > >> feature, so the hal_ppmc.c driver does the sampling by a software > >> command. This causes some jitter in the sampling time. On an > >> X86 machine with decent latency performance, this has been OK, > >> but not optimal. Since we are now contemplating moving to > >> other platforms, such as the BeagleBone, with somewhat worse > >> latency jitter, and having to rework rtapi to adapt to other RT > >> packages such as Xenomai, this might be a good time to > >> explore whether triggering a HAL thread via external interrupt > >> is possible and/or desirable. I would certainly like that option, > >> as it would reduce position sampling jitter to sub-ns levels for > >> one board, and no more than 1 us ever on multiple boards. > >> Michael has some other reasons for allowing external interrupts > >> on some systems, but doesn't want to go all the way through to > >> HAL threads with it. Does anyone else have thoughts on this, > >> or want to be able to trigger HAL threads externally? I can > >> imagine some other projects that might benefit from this. > >> > >> Thanks for any thoughts, > >> > >> Jon > >> now > > > > While 10khz sounds a little slow for us stepper users, the fact that > > the > > I think Jon is talking about timing the servo thread. > > -m
I agree with that assumption, but if applied to the base_thread in a software stepper scheme, using hardware to capture the encoders state, I think it would be magnitudes easier to arrive at a relatively noise free error output to feed back to the PID machinery. As is, it has to be rate and/or lowpass filtered before feeding into the PID before the rest of the PID 'adjustments' even begin to work as expected else the PID seems overwhelmed by the noise. It looks great on my scope, within a degree of true quadrature on any edge, at nearly any steady speed down to about 1.5 rps. Below that of course, the noise takes over and the actual speed obtained may deviate quite a bit, not enough mass in the drive and chuck to steady it. Extremely audible from the X motor when running a G33.1 cycle at 150 rpm, it, X, sounds like a hacksaw with random missing teeth. Better, but still a raucous tone during the cut stroke when running a G76 cycle at 700 or more rpms. The resultant threads however, don't appear to suffer because of it if my tool is sharp. Thanks Michael. 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> is up! My views <http://www.armchairpatriot.com/What%20Has%20America%20Become.shtml> Time goes, you say? Ah no! Time stays, *we* go. -- Austin Dobson A pen in the hand of this president is far more dangerous than 200 million guns in the hands of law-abiding citizens. ------------------------------------------------------------------------------ Learn the latest--Visual Studio 2012, SharePoint 2013, SQL 2012, more! Discover the easy way to master current and previous Microsoft technologies and advance your career. Get an incredible 1,500+ hours of step-by-step tutorial videos with LearnDevNow. Subscribe today and save! http://pubads.g.doubleclick.net/gampad/clk?id=58040911&iu=/4140/ostg.clktrk _______________________________________________ Emc-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-developers
