[time-nuts] [Solved] Looking for multiple PPS timestamp logging

Don Latham djl at montana.com
Mon Oct 3 19:14:12 UTC 2011

Hi Hal: been watching this thread with some interest. Seems to me that
the layers that the MS operating systems and bios(es) put between the
parallel port and the programs using the port could introduce a lot of
variable latency. I think there may be some available dll's that go
around the shells?

Hal Murray
>> I was thinking about the parallel port polling idea, but then my son
>> wanted
>> to measure the relation between temperature and XO frequency, so we
>> needed
>> microsecond resolution.
> Why do you need microsecond resolution?
> A junk XO will drift ballpark of 1 PPM per C.  That's 86 ms per day or
> 3.6 ms
> per hour.
> What sort of resolution do you think you can get from a parallel port?
> It might be fun to see how far you can push the parallel port.
> How about a loop like this:
> Initialization:
>   grab old time
>   grab old parallel port data
> loop:
>   grab new time
>   grab new parallel port data
>   if data changed:
>     grab newer time
>     log change that happened somewhere between old time and newer time
>   old time = new time
>   old data = new data
>   goto loop
> Post processing can filter out the occasional samples with a wide time
> window
> because the scheduler ran some other job at the wrong time.
> For extra credit...  Suppose  you are expecting PPS type signals and you
> know
> roughly where they are located within a second.  There is no point is
> spinning when you aren't expecting something to happen.  So you can
> sleep
> until a bit before the next event.   That will let the scheduler run
> other
> jobs.  Hopefully it will be nicer to you when you do want to run.
> --
> These are my opinions, not necessarily my employer's.  I hate spam.
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"Neither the voice of authority nor the weight of reason and argument
are as significant as experiment, for thence comes quiet to the mind."
R. Bacon
"If you don't know what it is, don't poke it."
Ghost in the Shell

Dr. Don Latham AJ7LL
Six Mile Systems LLP
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POB 134
Huson, MT, 59846
VOX 406-626-4304

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