[time-nuts] gpsd 1pps pulse?

Hal Murray hmurray at megapathdsl.net
Mon May 6 18:24:12 EDT 2013


caf at omen.com said:
> What are the requirements for the 1 PPS signal fed to the carrier detect
> pin? I presume the 10 us 1pps from the Thunderbolt is too narrow. 

Sometimes it works.  Sometimes it almost works meaning that it works well 
enough to look like it's working but only some of the samples are getting 
captured and it may drop out when something changes.  I'm not sure of the 
details.  I assume some hardware doesn't actually save the right info and/or 
some software looks at the current status rather than the saved bit.

I suggest plugging it in and looking at the counters.

You have to do something like this (as root) to get started:
  ldattach 18 /dev/ttyS0

Then just
  cat /sys/class/pps/pps0/assert
Then wait a while and look again and see if the counter went up at 1 per 
second.

You will get things like this:
  1367878436.999973687#17737425
The stuff before the # is the time stamp.  The stuff after the # is a counter 
that gets bumped on each interrupt.


> I assume the rising edge of CD is the one gpsd triggers on.

Is there a reason you want to use gpsd?



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