Hi Just to be clear, your peer delay numbers for the Pi show and improvement from 0.5 ms down to 0.3 ms with some tweaks. A “non-usb” ethernet setup can get those delays down much further. In the context of the original question “tweaking the USB drivers” this is what was being addressed.
Bob > On Jun 14, 2015, at 2:17 AM, David J Taylor <david-tay...@blueyonder.co.uk> > wrote: > > Hi > > At best, simply because of the way that USB interface works, you can go from > the ~1/2 ms range into the ~1/4 ms range. Rewriting the low level drivers may > be required. This compares to an equivalent lag on a device with a built in > ethernet of < 0.001 ms. The easy thing to do is to simply kill off everything > else that is running on the device. That goes double for anything running on > USB (keyboards / mice etc). > > Since you can get boards with built in (integrated in the MCU) ethernet for > < $50, it’s not clear how much tweaking time this is worth. You don’t get any > real use out of the Pi’s fancy graphics in this case. The board really is not > optimized for doing this sort of thing. Also - check the threads on Pi heat > sinking and boards burning out. If you plan to use this full time - invest > the money in cooling now. > > Bob > ================================== > > Bob, > > Thanks for your comments. I made a simple comparison between the RPi and the > BBB with help from the folks here, and wrote it up here: > > http://www.satsignal.eu/ntp/BBB-vs-RPi.html > > Using NTP, the reported RMS offset on a client on the same LAN was 18 > microseconds (BBB) and 39 microseconds (RPi), and the mean RMS jitter was 7 > microseconds (BBB) and 29 microseconds (RPi). So the USB/Ethernet does make > the RPi less good as a server, but depending on your application it may still > be more than adequate. Neither system provides "microsecond" level, both are > more than adequate for "tenth millisecond" level. > > The BBB generated sufficient RF interference to stop a near-on-board GPS from > working. > > I have had no overheating troubles with the 9 RPi systems here, none have > needed added cooling, and none have burnt out. One is even running > Windows-10 IoT. > > Cheers, > David > -- > SatSignal Software - Quality software written to your requirements > Web: http://www.satsignal.eu > Email: david-tay...@blueyonder.co.uk > _______________________________________________ > 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. _______________________________________________ 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.
