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 samples are frozen in a very accurate timebase would appear to be a worthwhile endeavor to me. with say a 30 to 50 khz clock, the base thread could be clocked entirely in hardware. That can't help but be an advantage for stepper drivers I'd think. OTOH, I have no clue just how big a re-write that might be. I can't imagine it would be trivial. A change that big should probably be staged to simmer in the devel branch until 3.0. Interesting times Jon. 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> Favorite Windows game: "Guess what this icon does?" 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
