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Re: [gpsd-dev] Implementing support for additional message in u-blox dri

From: Gary E. Miller
Subject: Re: [gpsd-dev] Implementing support for additional message in u-blox driver
Date: Fri, 11 May 2018 09:55:59 -0700

Yo Michael!

On Fri, 11 May 2018 11:18:52 -0400
Michael Pratt <address@hidden> wrote:

> I have been working with gpsd and a u-blox M8T receiver, and I have
> some questions about the u-blox driver implementation and the
> messages that are supported.


> 1) gpsd supports the NAV-TIMEGPS message, which "reports the precise
> GPS time of the most recent navigation solution ...". Some u-blox
> protocols also implement similar messages for GLONASS, Galileo, and
> BeiDou (NAV-TIMEGLO, NAV-TIMEGAL, and NAV-TIMEBDS, respectively), but
> these are not supported by gpsd.

Yeah, mostly because they are now, and no one cared enough, yet, to 
submit a patch.  Adding them would be easy.

> Would there be any advantage to
> supporting these messages?

Not that I see, except for educational value.  The differences between
UTC as reported by GPS, GLONASS, GALILEO, etc. are tiny (nano seconds),
and already factored into the nav solution the GPS calculates.

> 2) u-blox also implements a NAV-TIMEUTC message which reports a "UTC
> Time Solution", which is also not supported by gpsd. However, the
> NAV-PVT message already reports UTC time. Would implementing support
> for the NAV-TIMEUTC message be redundant?

Yup.  Just two places for the same data.

> 3) Why are NAV_SVINFO messages required to have a payload of at least
> 152 bytes?

Not according to the doc: "Length (bytes) 8 + 12*numCh"

But I see ubx_msg_nav_svinfo() assumes 152.  That is a bug.  I
just pushed a patch for that.  Thanks for spotting that!

Oddly the patch to accept shorter NAV-SVINFO messages changed none
of the regressions.

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        address@hidden  Tel:+1 541 382 8588

            Veritas liberabit vos. -- Quid est veritas?
    "If you can’t measure it, you can’t improve it." - Lord Kelvin

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