On Wed, 5 Dec 2012, Stefan Tauner wrote: > > 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. Your theory omits an important point: The host system generally doesn't care exactly when frames start. Forcing it to keep track of these events adds overhead. > 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. It may not be all that advantageous after all, because you still have to unicast the information for relating timestamps to SOF packets. Since you have to do this anyway, you might as well use those unicast packets for synchronization instead of the SOF packets. > 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 :) Exactly: _If_. Alan Stern -- 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
