On Tue, 2012-08-28 at 14:12 +0200, Per Jessen wrote:
Roger Oberholtzer wrote:
On Tue, 2012-08-28 at 10:14 +0200, Per Jessen wrote:
NTP knows about transmission delays and all that - to be honest, I don't know how accurate it is, I have nothing to compare to. I am not concerned about milliseconds myself, but I suspect that is the level of accuracy achievable.
I have read that inexpensive receivers, like in consumer grade clocks, should be able to achieve 0.1 sec accuracy. Better receivers can do better.
I could be way off, but I don't think it is related to the receiver quality. After all, either you've got a signal or you don't. What is done with the data received is probably more important, and that's where NTP comes in.
The DCF77 wikipedia entry (correctly?) states that inexpensive receivers typically have a 10 Hz bandwidth, and thus have this limitation. Not sure what that means. For this kind of sync, it is not the frequency of the update, but the accuracy of it when it arrives. This is a bit beyond my expertise.
But, returning to the thread, would this be the case when a USB adapter is added? I know that such solutions do not work with serial port GPS that provide a PPS, resulting in far less accurate time synchronization. Maybe the parallel or serial port versions of these devices require access to a physical interrupt line that is not possible when USB is used?
Using a PPS is a different solution, but I have also seen people having trouble with USB and PPS sources.
By 'Trouble' you mean it does not work. USB cannot propagate the PPS signal with the same accuracy as the serial port. Some don't even look at it. I checked the kernel drivers a while back to see what each USB serial adapter supported. They are geared more to tty control for things like modems. Yours sincerely, Roger Oberholtzer OPQ Systems / Ramböll RST Office: Int +46 10-615 60 20 Mobile: Int +46 70-815 1696 roger.oberholtzer@ramboll.se ________________________________________ Ramböll Sverige AB Krukmakargatan 21 P.O. Box 17009 SE-104 62 Stockholm, Sweden www.rambollrst.se -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse+owner@opensuse.org