[ntp:questions] ntpd: time reset problem

Unruh unruh-spam at physics.ubc.ca
Thu Sep 24 15:12:20 UTC 2009

David Lord <snews at lordynet.org> writes:

>James Browning wrote:
>> On Sep 17, 10:52 pm, "David J Taylor" <david-tay... at blueyonder.not-
>> this-part.nor-this.co.uk.invalid> wrote:
>>> Don't worry about trees - a modern GPS such as the GPS 18x LVC is very
>>> sensitive, and can work with a lot of obscuration.  Although my GPS 18 LVC
>>> is sitting on the roof, the GPS 18x LVC works just as well sitting in a
>>> room on the top floor of the house.
>> I have a SiRF star III based USB dongle (US GlobalSat BU-353)</plug>
>> that I got a location off of in a basement room about 6 feet from the
>> window. currently it's attached to box whos' ntpd crashes every time
>> I
>> mention it. I think it's talking in the binary mode and the kernel
>> device
>> is tuck at the wrong speed. (I probably just need to restart it.)

>You can check with minicom or similar as to output. I used
>Telix from DOS with my BR304 to set to just give a single
>RMC sentence per second output. The codes needed to switch
>modes were in the br304 manual I downloaded.

>Having said that the br304 is now in pieces to be explored
>with scope probe in case it's possible to locate any signal
>usable for ntp. Best I had was +/- 0.5 sec but it is much
>less sensitive than the Garmin GPS18x-LVC that early in year
>maintained an offset within 4us (that's until sats in view
>reduced by tree growth so it became unusable).

Since the usb line has nothing to which a PPS interrupt could attach
AFAIK, you are not going to get even ms timing from a usb dongle. You
should certainly get better than .5 sec however.




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