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Re: [gpsd-dev] PPS glitch - Venus chip
From: |
Hal Murray |
Subject: |
Re: [gpsd-dev] PPS glitch - Venus chip |
Date: |
Sun, 31 Jan 2016 13:36:52 -0800 |
address@hidden said:
> Can you see in your sccope if the first sentence completes befoe the PPS
> edge?
The PPS timing looks good. Attached is 2 seconds of NMEA data. (This is
also a test to see if my mail software is dumb enough to put line breaks into
attachments. You may have to put things back together.)
The second column is seconds this day. The 3rd column is the length of the
line including CR/LF.
The first sentence of a clump is GPGGA. It's 77 bytes long. At 9600, a
character is 1 ms. The earliest time-within-second that I see is 133 ms, but
that's only from a sample of ~100 seconds.
>From last night, I don't remember anything starting earlier than 20-30 ms.
So I don't think many sentences are arriving before the PPS.
In case it matters, I just noticed that the time data in the GPGGA and GPRMC
sentences both include a fraction of a second. The ".928" was the same in
all the samples I captured.
Keep in mind that this problem only happens some of the time and the time
scale on switching between good and bad is hours so any data we are looking
at may be for either the good or bad case. I haven't figured out how to
capture data while gpsd is running. Looks like wireshark can do it.
> gpsd uses the leading edge. It does not ccare about polarity.
That's what I was expecting. But when I plot the data, it's 4 ms late.
I get reasonable results with ntpd after fudging to use the clear edge rather
than the default assert edge.
nmea.log
Description: nmea.log
--
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- [gpsd-dev] PPS glitch - Venus chip, Hal Murray, 2016/01/30
- Re: [gpsd-dev] PPS glitch - Venus chip, Gary E. Miller, 2016/01/30
- Re: [gpsd-dev] PPS glitch - Venus chip, Hal Murray, 2016/01/30
- Re: [gpsd-dev] PPS glitch - Venus chip, Gary E. Miller, 2016/01/30
- Re: [gpsd-dev] PPS glitch - Venus chip, Hal Murray, 2016/01/30
- Re: [gpsd-dev] PPS glitch - Venus chip, Gary E. Miller, 2016/01/31
- Re: [gpsd-dev] PPS glitch - Venus chip, Hal Murray, 2016/01/31
- Re: [gpsd-dev] PPS glitch - Venus chip, Gary E. Miller, 2016/01/31
- Re: [gpsd-dev] PPS glitch - Venus chip,
Hal Murray <=