> j...@miles.io said: > > Agreed, nobody should be using RS232 for anything nowadays. > > RS232 works much better for capturing PPS timing.
Unless you are watching it with a ring-0 (kernel) driver, and/or using a hard realtime OS to run the client software, it really won't matter that much. Anyone running Windows or most flavors of Linux has more to worry about than the distinction between USB and RS-232, when it comes to latency. For truly critical applications it's best if the counter itself does the timestamping. For ordinary NTP use on Linux or Windows the distinction between RS232 and USB is pretty questionable. Submillisecond jitter has been documented in USB PPS applications (e.g., https://lists.bufferbloat.net/pipermail/thumbgps-devel/2012-March/000109.htm l ), albeit with unspecified latency. If that's not good enough, you need to tackle the issue somewhere besides the physical layer. > Another advantage of RS232 over USB is that the configuration is stable when > things get unplugged and replugged, or powered off, or ... Of course, that's > a disadvantage if your program wants to know when the gizmo got unplugged. USB devices have gotten a bad reputation in this regard because of developers' failure to understand the idea behind serial numbers. As with noise immunity, it's possible to do it right, it's just that too many people don't bother. -- john, KE5FX Miles Design LLC _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.