[Interest] Packet arrival-time resolution? QUdpSocket

[Konstantin Tokarev]

30.11.2017, 18:49, "Jason H" <jhihn at gmx.com>:
>>  Sent: Wednesday, November 29, 2017 at 11:05 AM
>>  From: "Thiago Macieira" <thiago.macieira at intel.com>
>>  To: interest at qt-project.org
>>  Subject: Re: [Interest] Packet arrival-time resolution? QUdpSocket
>>
>>  On Wednesday, 29 November 2017 01:34:05 PST Konrad Rosenbaum wrote:
>>  > Any software working on a scale below 10ms needs to be realtime. Qt is not
>>  > realtime. Sorry.
>>
>>  That's why the API I'm creating will give you a QDateTime, which only has
>>  millisecond resolution.
>>
>>  I thought briefly about using QDeadlineTimer (which has nanosecond), but gave
>>  up since it wasn't necessary and I couldn't get the monotonic timer on most
>>  OSes.
>
> Consolidated reply,
> The speed of light is ~1ft per ns, and your clock is running at ~0.33-1 ns. There's plenty of factors to prevent absolute best performance, not even including that the speed of light in a wire is about 1ft per 3ns, due to inductance (multi-layer PCBs also slow it down). Meanwhile the speed of sound is ~1.1ft per ms at STP. If I can get reliable 1 ms packet resolution and accuracy I'll be fine. I can alter the data and node configuration to support some jitter. As long as the hosts accurately record the event on local clock time, and I know the offsets of each clock, can calculate the true event time. If they are all sub ms deviation, then I can take it as-is and know I'll be within 13 inches.
>
> I don't think you can say that Qt is not real-time. That's more of a kernel issue than a software library issue.

Actually, Qt is ported to real-time operating systems, such as QNX and Integrity

>
> So definitely I need to use P2P for usec sync of the clocks.
>
> But I think as networks and CPU clocks get faster, that 1 ms will seem like an eternity. I seem to be working just at that ms/usec boundary...
>
> Thanks for all your help!
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-- 
Regards,
Konstantin