In message <[EMAIL PROTECTED]>, Nate Williams writes:
>> : You may not know the answer to this, but it's worth a shot. Wht kind of
>> : accuracy can we expect using 'cheap' off-the-shelf GPS receivers?
>>
>> We're getting, with ntp4 on a 3.x kernel, about +- 4uSec with a cheap
>> gps receiver + atomic clock on a i486 class machine.
>
>I've got the cheap gps receiver (Garmin 12XL), but what do you mean by
>an 'atomic clock'? Should the GPS receiver's NMEA messages be adequate
>enough to do the job? However, all I need is ms accuracy, so anything
>below 500us is good enough for me.
If you only have NMEA you will have a hard time. At 1200 baud you
get 50 usec jitter just from the rxclock in the uart (16 * 1200),
not to mention how exact the NMEA is transmitted in the first place.
There is a pretty vanilla NMEA refclock, so the easist way to find
out is to try it out next to (in a network sense) a stratum 1 NTP.
--
Poul-Henning Kamp FreeBSD coreteam member
[EMAIL PROTECTED] "Real hackers run -current on their laptop."
FreeBSD -- It will take a long time before progress goes too far!
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