[ntp:questions] How bad is USB?
uwe_klein_habertwedt at t-online.de
Sun May 10 11:41:16 UTC 2009
David J Taylor wrote:
> Uwe Klein wrote:
>> David J Taylor wrote:
>>> Richard B. Gilbert wrote:
>>>> You can try it and see what happens! The results may be
>>>> sufficiently good for your purposes. You will almost certainly not
>>>> get microsecond accuracy. If you are willing to settle for +/- 10
>>>> milliseconds you can almost certainly get that.
>>> My first tests show within a millisecond or so:
>> Do I see a (sawtoth) beat signal between "true" time and the
>> nominally 1ms polling interval from the usb bus?
> I don't think so. If you mean the sawtooth on the left, peaking at 1600
> the first day and 0800 the second, that's pure temperature variation.
Yes, that's what caught my eye.
> PC Narvik was not switched to USB/serial until about 1530 on day 2.
> There is an increased fine-grain variation in the offset after the
> change, but the jitter reported by NTP has dropped from 110-140
> microseconds to about 45 microseconds after the switch from LAN-sync to
> There are more performance graphs here:
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