Hi
> On Dec 14, 2014, at 4:26 PM, Hal Murray <[email protected]> wrote: > > > [email protected] said: >> Based on my recent testing - including Solaris - you will be better off with >> the Internet unless your USB adapter is far better behaved than the several >> I have here > > That depends, (TM) > > How good/bad is your network connection? Mine gets over 3 seconds of queuing > delays. I challenge anybody to find a USB device that bad. > > There are only 2 or 3 significant vendors of USB-serial chips. I think they > are reasonably well supported by all major OSes. > > USB is polled, so interrupt latency turns into polling latency. I think the > polling cycle is 1 ms for slow things like serial ports. On at least some (= the ones I’ve seen) of the serial devices, they will continue to buffer if they have a character coming in. Put another way, a string sent at 19.2 Kbaud will likely transfer as a block rather than a character at a time. Is this at the bus or the driver level? - who knows. The result (in Linux / Win-dooze / or OS-X) is that data comes in in bursts. > Maybe 1/4 ms for > faster things like disks. At the system level, faster polling means more > overhead and slower polling means bigger buffers. > > Many of the low cost GPS units use the SiRF chips. They have a wander of > ~100 ms. I said wander rather than jitter because it's very slow as in > hours. You can't filter it out with a 10 or 100 second sample. .. as in a pps output is not necessarily a *useful* pps output. Only useful outputs count. We’ve been over the why and the how of chips that put out pps’s way late a number of times. Simple answer - it didn’t matter in the firmware design spec. Bob > > The old Garmin GPS-18-USB (not 18x) units had pretty good timing. No wander. > Unfortunately, they weren't very sensitive. > > > -- > These are my opinions. I hate spam. > > > > _______________________________________________ > 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. _______________________________________________ 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.
