Subject: Re: supported GPS time receivers for NTP service?
To: None <>
From: Wolfgang S. Rupprecht <>
List: current-users
Date: 12/20/2004 22:40:08
>   1) Does NetBSD support any type of GPS receiver with a PPS feed?

I'm running a Motorola M12 Oncore on -current (and have for the last
year or two).  I picked up a developer's kit from Synergy
( a few years back for $99.  Unfortunately
the prices vary wildly for these kinds of kits, and I don't see
anything available cheaply that comes with the ttl-to-rs232 adaptor
board you'll need if you want to hook this up to a comm port.

The PPS appears to have will under 1ms fuzz, but I don't have any real
way of measuring that other than trusting what ntpd prints out with
"ntpq -p" and puts into the clockstats file.

> See src/sys/dev/ic/com.c in 2.0; PPS support appears to be there.
> It's not clear to me how complete it is, or how well it works.

PPS has 2 modes, one where the kernel uses the PPS signal to steer an
in-kernel software oscillator.  This mode is doesn't work very well
and is deprecated as far as I can tell.  There is another mode where
the PPS simply timestamps the PPS transition and then passes that up
to userland and into a software oscillator running inside ntpd.  That
mode works fine and is the mode I've been using.

Wolfgang S. Rupprecht      
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