[ntp:questions] Re: Q: Possible to use Haicom HI202e USB GPS recv'r as refclock

Ulrich Windl Ulrich.Windl at RZ.Uni-Regensburg.DE
Mon Sep 15 14:25:09 UTC 2003


"Robert MacKinnon" <rbm at doglover.com> writes:

> I've just gotten one of these GPS receivers with the intent of setting up a
> Linux box as a Stratum 1 server.  The Haicom is based around an Evermore GPS
> module and outputs RMC, GGA and GLL sentences.  I have two concerns that
> might hinder this receiver to be used as an NTP refclock
> 
> 1. I don't know the command to limit the NMEA output to just RMC
> 2. Can PPSkit support a USB connected receiver?

Regarding "USB connected receiver": AFAIK, even USB "interrupt mode"
requires the CPU to _poll_ the USB controller. So when being done 100
times per second, it does not make any sense unless the USB controller
can time-stamp pending messages with high resolution, leaving open how
to synchronize that clock.

So I think when you care about the second, it's OK, but when you care
about microseconds, you are having a problem.

> 
> Has anyone tried this GPS receiver under NTP and can confirm that it
> works?

Regards,
Ulrich




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