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Re: [gpsd-dev] Time autonomy

From: Gary E. Miller
Subject: Re: [gpsd-dev] Time autonomy
Date: Tue, 24 Feb 2015 13:32:10 -0800

Yo Terje!

On Tue, 24 Feb 2015 22:13:56 +0100
Terje Mathisen <address@hidden> wrote:

> > Not the case on a RasPi.  No battery back clock, and often a lot
> > of downtime.
> Including downtime caused by simply pulling the power cable/battery,
> right?

Be careful, I resemble that remark! :-)
> >> 6. If you had to increment saved_epoch in step 3, write it
> >> /var/run/gps-epoch at shutdown time.
> > But only if you knwo the gps-epoch to save is good.
> If you have no cmos clock and no network connection, the best you can 
> possibly do is to update the epoch file every time something
> interesting happens, i.e. leap second or week counter rollover. To
> guard against sudden power loss, this should be done asap and not
> wait for a regular shutdown event.
> If the device is left without power for so long that you miss one of
> the edges, then you'll need some manual method to get it back in sync.

I guess if gpsd saved a copy of the GPS week every time it rolled over
we could detect an epoch roll over.  Then gpsd only needs a good GPS
lock, and write, every epoch.

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97701
        address@hidden  Tel:+1(541)382-8588

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