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
2.) By some chance, are you looking at the 60 Hz power system through
a UPS (Uninterruptable Power System)? They can generate wave shapes
of the type you are seeing, and some make decisions on a cycle by cycle
basis.
==
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