[time-nuts] [Solved] Looking for multiple PPS timestamp logging
hmurray at megapathdsl.net
Tue Oct 4 10:36:22 UTC 2011
> The temperature swings won't be large, just the usual diuneral indoor cycles.
In California, the diurnal temperature swings are big enough to be useful. :)
This is what ntp sees the main/CPU crystal doing in a non airconditioned
room. Each color is a different day.
The swing would be much bigger outside, especially with an open sky.
> Since we'd be measuring 4 PPS signals that won't be in phase, I wasn't
> planning on sleeping for long. But, I some 10 usec sleeps with usleep(10000)
> after reading a pulse would be reasonable. But, with the system not doing
> anything but polling and writing to the disk, I wasn't expecting much
> interruptions from other processes.
I was thinking of keeping track of when you expected each pulse to arrive
next and sleeping until a little before you expected the soonest one.
(Adjust "a little" by trial and error.)
I agree that Tom's picPET will be a fine way to do it. I was just playing
with how to do it with the parallel port.
It's still an interesting question of how accurate you need to measure the
time. That's probably a good one to work through with your son on the back
of an envelope.
How are you measuring temperature?
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