On Dec 1, 5:11 pm, Dave Hart <daveh...@gmail.com> wrote: > On Dec 1 16:58 UTC, jack wrote: > > > I have a related question: given that my system clock is synced to an > > external GPS within ms, how do I read time that gives me the same > > accuracy? When I tried to read time at 60Hz, I found that the times > > returned are not periodic, sometimes even the same. > > Depending on the version of Windows, hardware, and the interface used > (GetSystemTime[AsFileTime] vs timeGetTime/GetTickCount) the best > resolution you can get for the clock is 0.5ms, the worst about > 15.625ms. To do better you need to query ntpd using the NTP protocol > -- gin up a mode 3 (client) packet and send it to UDP 127.0.0.1 or ::1 > port 123 and grab the time from the resulting mode 4 response. You > can look at the sntp source code (not yet ported to Windows) for a > guide. > > Cheers, > Dave Hart
Dave, Thanks for the query suggestion. That is what I plan to do. I am now looking at ntpq code. I plan to query ntpd periodically and use the high performance counter to keep time in between. If the query time is negligible, I should get very accurate time. However, I have no way of calibrating the query time. Jack _______________________________________________ questions mailing list questions@lists.ntp.org https://lists.ntp.org/mailman/listinfo/questions
