Re: [gpsd-users] Trouble Receiving Time from Delorme EarthMate USB (LT-20)

[Gary E. Miller]

Yo Jeff!

On Wed, 13 Mar 2019 08:47:20 -0700
Jeff Morris <address@hidden> wrote:

> I recently came across a Delorme EarthMate USB (LT-20) at a thrift
> shop for a couple of bucks, and picked it up with the hope of being
> able to use it as an NTP stratum-0 time source for an NTP server on
> my home network.

Ever wonder why it was so cheap?  You can buy real good new GPS
for around $10.

> I've managed to get gpsd installed and running, and it sees the 
> EarthMate. The EarthMate acquires satellites and gets a fix and shows
> my correct position, so it seems to be working properly. However gpsd
> is reporting a date from the EarthMate far in the future. For example
> for today, 2019-03-13, it's reporting the date as 2099-07-28. The
> time is correct, but the date is way off. If I look at the raw time
> in seconds-since-the-epoch format, I see numbers like 134439.000.
> (These numbers are both from the output of gpsmon.)

Surprise, your unit has the GPS week rollover bug...

> I've added the following lines to /etc/ntp.conf (and removed all
> other servers):
> 
> server 127.127.28.0 minpoll 4 maxpoll 4 prefer
> fudge 127.127.28.0 time1 0.0 refid GPS

NTP Classic or NTPsec?

> However, ntpq -p reports that it has never successfully polled this
> source:

Before you look there, does the cgps output look good?  What does
"ntpshmmon" show?

My guess would be that the bad date has the time stamp thrown away.

> I'm aware of the GPS week rollover issue, and given that this is an
> old receiver that I picked up at a thrift shop it may very well be 
> susceptible to that.

You already confirmed that with the bad date.

 However, the numbers I'm seeing don't make any 
> sense to me. The 10-bit week rollover issue should result in a
> rollover every 20 years? The date I'm seeing is 80 years in the
> future

Yup.  A century minus 20.

The Delorme were not very good when they were new, and now they are
really old...

RGDS
GARY
---------------------------------------------------------------------------
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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