[Interest] Packet arrival-time resolution? QUdpSocket

Konrad Rosenbaum konrad at silmor.de
Wed Nov 29 10:34:05 CET 2017


Hi,

On Tue, November 28, 2017 17:34, Jason H wrote:
> It looks like Linux will support usec and even nsec resolution timestamps.

yes it does. However: please keep in mind what a nanosecond is! This is
the time that light needs to cross about 30cm (~ 1 foot) - in other words
in an ideal world this would be the time that a signal needs to propagate
across a regular PC mainboard. In the real world the speed of signals in
copper wires is significantly below this - firstly because the "speed of
light in copper" is only 50% of the speed of light in a vacuum and
secondly because chips have delays.

Getting computers to sync to milliseconds is quite feasible with NTP.
Microseconds may need PTP. Below this you need to know intricate hardware
details that the manufacturers are loathe to give to you (mostly because
they don't have them, partly because they are embarrassing).

Any software working on a scale below 10ms needs to be realtime. Qt is not
realtime. Sorry.


    Konrad




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