Subject: Re: supported GPS time receivers for NTP service?
To: None <email@example.com>
From: Wolfgang S. Rupprecht <wolfgang+gnus20041220T220540@dailyplanet.dontspam.wsrcc.com>
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
(http://www.synergy-gps.com/) 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 http://www.wsrcc.com/wolfgang/
firefox - 10 million downloads in one month
explorer - when free isn't good enough