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

Hal Murray hmurray at megapathdsl.net
Tue Oct 4 06:36:22 EDT 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?

These are my opinions, not necessarily my employer's.  I hate spam.

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