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Re: [gpsd-dev] Very basic PPS question:

From: Eric S. Raymond
Subject: Re: [gpsd-dev] Very basic PPS question:
Date: Sat, 19 Oct 2013 13:36:21 -0400
User-agent: Mutt/1.5.21 (2010-09-15)

Paul Fertser <address@hidden>:
> 2. "Confirm that the UTC offset has been downloaded ... and that the
> receiver is generating 3D fixes... Capture the time from the ZDA
> packet. Once time is acquired, add 1 to the whole second on the next
> PPS for the correct time". [2]

Yeah, that's a sort of ass-backwards way of saying the PPS comes first.

> I'm not sure how you plan to deal with the fact that there's no
> standard way to learn if the receiver already knows the current amount
> of leap seconds or not; for MTK a proprietary $PMTK457 command is
> available, but even that doesn't help much: on earlier models it just
> outputs the current assumed offset, so you'd need some external data
> to verify its correctness.

There is in principle no way to know this.  All you can do is wait long
enough after device open for the next ephemeris download to have happend
(30 minutes should lock that in).
                <a href="";>Eric S. Raymond</a>

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