On Tue, 4 Dec 2012 16:27:00 -0500 (EST) Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > I don't think referencing times to SOF packets is the best approach, > although it probably is the approach that would yield the most > precision. How precise do you want your synchronization to be? It should be below 1ms accuracy, but being more precise does never hurt of course :) BTW anyone interested in really accurate USB synchronization should read the paper "Sub-nanosecond Distributed Synchronisation via the Universal Serial Bus"; they use custom hardware though. > Running NTP over a USB-based network link would certainly be the > easiest solution, if your device can support it. Over the long run, it > might even be more accurate on average than using SOF packets. We are talking about microcontrollers with a few kB RAM at most, so just cross-compiling any (S)NTP client wont cut it probably :) So the SOF approach seems to be way more elegant and easy to implement to me... in theory. Another nice property is that SOF packets are sent for every frame in any case (but errors) and they are broadcasted, which is both advantageous regarding bandwidth usage and independent of the number of devices attached. Regarding long-term stability/precision i am not sure i can agree with you. If i throw the same amount of statistics/algorithm complexity at the SOF scheme and a software-exclusive approach i dont see how the latter could be better :) -- Kind regards/Mit freundlichen Grüßen, Stefan Tauner -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
