> I stand firm that the only proper way to do this is with a 100% > deterministic architecture.
> ..only proper way to do what? The goal is to discipline the internal > software clock to GPS. A typical application is a database server > that is running a web e-comerse site so that transactions get time > tagged. So you would run a web, file or database server on a > deterministic, no cache micro controller? > In the original message, Mike is trying to get the jitter better than 20e-6 on a pc. I don't believe this falls in the typical use of NTP category. What i assume here is that the jitter is local to the machine sampling the 1pps signal. Otherwise this is moot. Numerically... 1/(20e-6) = 50e3, likewise with nyquist variance (50e3 x2) = 10e3, or time domain that is 100khz wide. This tells us that the input of the pc must be rate monotonic to 100khz. The only thing that i can think of that comes close to this monotic bw is a 192khz sound card, i have to assume these cards are rated in raw sampling rate and not nyquist, so correcting we see (192khz /2) = 96khz bw. Pretty close to 100khz. Maybe close enough when considering both sides of figure contain the correction for twice the highest bw. Assuming i did not fat finger a calculation, a 192khz sound card is another possible solution to the problem. The sound card approach would permit conversion to the frequency domain and i think it would be fun to apply fourier analysis to something like a 1pps signal. Does anyone have any thoughts as to how stable an approach like this would be? Steve _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
