On 2013-12-19, David Taylor <[email protected]> wrote: > On 18/12/2013 19:59, Adrian P wrote: ...
> What accuracy do you need? I'm after millisecond level on Windows PCs, > which can be achieved with a PPS source, and should be even easier to > achieve in Windows 8.1 (compared to 7 or earlier). To sync a PC to the > full accuracy which a time-keeping GPS can deliver would take > considerable effort. It would be interesting to know whether anyone has > actually achieved that, and if so, how! Certainly Linux and FreeBSD are capable of microsecond, not millisecond, accuracy on modern equipment. For better than that, I think you would need special interrupt or timestamping hardware to get around the interrupt latency and variability of linux. While averaging the fluctuations, as chrony does, could deliver sub microsecond uncertainty, it is not clear you can get that accuracy due to average latency (Ie, if the timestamp on the interrupts is on average 1us late, all the averaging in the world will not get rid of that.-- That was the kind of figures I got when I timestamped a parallel port output pin transition and timestamped the parallel port interrupt that that pin was tied to-- 1-2us latency. Now that was many years ago, but I doubt that things have gotten better-- no reason for them to get better. Noone else really wants that kind of low latency interrupts, and interrupt conflicts cause much more variation than that. _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
