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Re: Questions (Answered)
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From: |
Gary E. Miller |
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Subject: |
Re: Questions (Answered) |
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Date: |
Wed, 22 Jun 2022 21:19:20 -0700 |
Yo Ken.Hendrickson---!
On Wed, 22 Jun 2022 21:17:30 +0000
Ken.Hendrickson--- via <gpsd-users@nongnu.org> wrote:
> I have found more information that answers most (if not all) of my
> questions.
>
> The gpsd.8 man page indicates that gpsd can use the Zodiac binary
> data.
Yup. But. I have never seen a Zodiac, and I don't think they have been
made in over a decade. The one and only Zodiac regression test we
have is from 2005. There may be some bit rot.
> Austin's Nerdy Things describes a microsecond accurate solution on a
> Raspberry Pi w/ 1PPS.
> https://AustinsNerdyThings.com/2021/04/19/microsecond-accurate-ntp-with-a-raspberry-pi-and-pps-gps/
That should be easy.
> Finally, I found these IETF documents:
> https://DataTracker.IETF.org/doc/html/rfc2783
gpsd implements that.
> https://DataTracker.IETF.org/doc/html/rfc1589
The Linux kernel implements that.
Check out the Timeserver HOWTOs hereO: https://gpsd.io
> This will give me a stand-alone time-frequency standard that will
> work as long as GPS is available. Differential GPS would hold no
> value for me, nor be practical if using the system portable or mobile.
No need for DGPS if 1 micro second is your goal.
> This web page shows pictures of some of the components (OCXO, Jupiter
> GPS, PLL board, PLL board schematic):
> http://www.DiyPhysics.com/2012/02/19/d-i-y-gps-disciplined-10-mhz-frequency-standard-gps-based-universal-time-clock/
Wow, steampunk!
> Can gpsd read the proprietary Zodiac binary message format? If not,
> I could write that software. Apparently, the time mark message which
> precedes the 1PPS pulse is only output in the 9600 bps binary message
> format, but not 4800 bps NMEA. (The UTC Time Mark pulse output
> message provides the number of seconds since the beginning of the
> week, about 0.5 second before the 1PPS signal.)
gpsd PPS can work fine with NMEA or Zodiac binary.
> What is currently the best way to utilize the 1PPS signal?
The ppscheck program from gpsd.
> Using the 1PPS signal seems to require being able to read the
> proprietary Zodiac binary message format.
No. But you'll get more data with the Zodiac binary.
> One objective I have, if possible, is to have a stand-alone time
> server with no internet connection. Is this possible? What would
> the gpsd requirements be?
See: https://gpsd.io/gpsd-time-service-howto.html
> Does anybody use differential GPS?
Yes.
> What would be required?
No.
> Would
> differential GPS only improve the geolocation solution, or would it
> also improve a time solution?
It improves both. With GNSS time == position.
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Seriously??
RGDS
GARY
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Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
gem@rellim.com Tel:+1 541 382 8588
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