The problem is the PPS needs to be referenced to the same clock the PC is using as a basis for system time. Yes, you could send the counter's value periodically but that has the same problem of sending the PPS, that is an un knowable delay.
The good news is that good Moterola GPS receivers with 50 nanosecond PPS accuracy are available on eBay for $15. Soyou don't have to mess with USB. On Tue, May 14, 2013 at 12:40 AM, Peter Monta <[email protected]> wrote: . > So a USB-based GPS should: > > - maintain a cycle count of its local crystal oscillator (e.g. with a timer > peripheral) > - report this count when requested > - timestamp PPS edges from the GPS module, and report these timestamps when > requested > > This would seem to be enough to gradually converge to a good estimate of > (USB_host_time - GPS_PPS) across the noisy USB link. > -- Chris Albertson Redondo Beach, California _______________________________________________ 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.
