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

From: Michael Pratt
Subject: Re: [gpsd-dev] Implementing support for additional message in u-blox driver
Date: Fri, 11 May 2018 14:23:44 -0400

Hi Gary,

Thanks very much for the insights, and for submitting that patch!


On 11 May 2018 at 12:55, Gary E. Miller <address@hidden> wrote:
> 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.
> Cool.
>> 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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