On Mon, 03 Sep 2012 12:00:53 -0500, Graham / KE9H <time...@austin.rr.com> wrote:
>On 9/1/2012 1:35 AM, Hal Murray wrote: >> The context is using the 60 Hz line for timing. >> >> I'm feeding 60 Hz from a wall wart transformer into a modem control signal >> that the kernel PPS stuff watches. Mostly, it works as expected, but >> occasionally, it picks or drops a cycle. >> >> In order to understand what was going on, I fed the same signal into the >> audio input and setup a job to capture the audio. Here is an example of a >> pick: >> http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Aug-09-a-pick.png >> http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Aug-09-a0.png >> http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Aug-09-a1.png >> >> OK, that somewhat makes sense. >> >> >> Something happened several days ago. I used to get picks/drops rarely, say >> ballpark of 1 a month. Now I'm getting 10 or 20 per day. So I started >> looking closer. >> >> I'm now seeing stuff like this. I've got lots and lots of examples. I added >> a second PC with different hardware. It sees the same stuff. >> >> Does anybody recognize this? >> >> http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Sep-01-a0.png >> http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Sep-01-b0.png >> http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Sep-01-c0.png >> http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Sep-01-d0.png >> http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Sep-01-e0.png >> >> >Hal: > >Two ideas: > >1.) You could have some process in Windows that is causing aperiodic >blocking of the OS's ability to process real time data. Can be many, >many causes. > >It is very common for a lot of the background processes that autonomously >run when you are not actively using the mouse and keyboard to cause these >type of problems. Back up utilities, virus checkers, USB WiFi accessories, >are examples. (The worst I have seen was the little CPU inside a (Dell) >laptop >battery, hanging up the USB bus, every time while it calculated the >charge in >the battery.) > >Windows is NOT a real time operating system. A fast computer that is not >heavily loaded can come close, but there is a lot of background stuff going >on in Windows that can aperiodically hang up a "lightly loaded" machine. > >Download a DPC tester (Deferred Procedure Call tester) and watch it >for an extended time that includes one of your "power glitches." > >http://www.thesycon.de/deu/latency_check.shtml You can add to this list the SMM (system management mode) routines stored in the BIOS. If those are causing the problem then the OS latency performance becomes academic. I have had to qualify motherboards and BIOS revisions before to avoid problems with them. http://en.wikipedia.org/wiki/System_Management_Mode#Problems _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.