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Re: [gpsd-dev] SemPiTernal - Bounding PPS uncertainty
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From: |
Hal Murray |
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Subject: |
Re: [gpsd-dev] SemPiTernal - Bounding PPS uncertainty |
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Date: |
Fri, 22 Apr 2016 00:08:42 -0700 |
> Connecting a TTL signal directly to a RS-232 modem control input pin ends up
> triggering on
Rats. Sorry for poking send too soon.
Connecting a TTL signal directly to a RS-232 modem control input pin ends up
with assert being the leading edge which is what ntpd uses by default.
(It also works in the normal case even through it doesn't meet specs. It
won't work as well if you have long cables.)
Aside from wrong-edge, the other problem you can get into is pulses too
narrow for software to notice. GPSDOs tend to have 10-20 microsecond pulses.
I think I have added counters to ntpd's clockstats for the PPS/ATOM driver
and the PPS handling in the NMEA driver.
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