[time-nuts] Time servers on a well known web site.
Hal Murray
hmurray at megapathdsl.net
Thu Jul 9 19:09:32 UTC 2009
> Wonder too just how accurate it is, using a USB based (non PPS) GPS?
The picture looked like a GlobalSat BU-353. I guess you could build a NTP
server out one, but I wouldn't expect time-nuts quality.
I've been looking for low cost GPS units that work well with NTP. I haven't
found much.
USB has a bad reputation for timing because it's polled, but that polling is
done in hardware on the order of a ms. You can sanity check things by
feeding a GPS with a serial connection to both a normal serial port and a
RS-232 to USB gizmo.
http://www.megapathdsl.net/~hmurray/ntp/GPS18LVC-usb-off.gif
I think this says that USB works reasonably well and my kernel/whatever isn't
getting the low-latency stuff right.
The old non-x Garmin GPS-18-USB was pretty good.
http://www.megapathdsl.net/~hmurray/ntp/GPS18USB-off.gif
The 18-x is pretty bad.
http://www.megapathdsl.net/~hmurray/ntp/GPS18LVCx-off.gif
Most of the low cost USB units seem to use the SiRF chip sets. They are
horrible for timing.
http://www.megapathdsl.net/~hmurray/ntp/GPSSiRF-off.gif
If anybody figures out how to get reasonable timing out of one of these
things, please clue me in.
--
These are my opinions, not necessarily my employer's. I hate spam.
More information about the Time-nuts_lists.febo.com
mailing list