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 ------------------------------------------------------------------------------ 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 Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers
