[ntp:questions] GPS clock for Linux

Uwe Klein uwe_klein_habertwedt at t-online.de
Sat Sep 13 08:31:29 UTC 2008

Hal Murray wrote:
> In article <ko8qp5-po8.ln1 at klein-habertwedt.de>,
>  Uwe Klein <uwe_klein_habertwedt at t-online.de> writes:
>>Hal Murray wrote:
>>>  There are a lot of low cost USB GPS gizmos that use the
>>>SiRF Star III.  They suck for timekeeping.
>>Is there a reason known for this?
> I assume it's a software bug/feature.  The problem is drift/wander
> in the offset.  The offset changes too slowly for normal
> jitter filters to work on it.
>   http://www.megapathdsl.net/~hmurray/ntp/GPSSiRF-off.gif
connected via serial/nmea or pps?

that looks like some beat frequency effect.
But it is much too slow/time too big
  to be sender and/or receiver uart clocking.

> I forgot to mention another problem with those chipsets.
> They have a leap second bug.
>   http://www.megapathdsl.net/~hmurray/ntp/leap-gps.gif


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