Additional pps-gpio

[Achim Gratz]

Hal Murray via devel writes:
>> PPS line discipline via USB virtual serial works and produces the expected
>> ~1ms offsets due to the USB poll interval.  It should be possible to remove
>> that shift by doing a loopback measurement via RTS/CTS eventually.  Jitter
>> is roughly on par with the local stratum-1 over network. 
>
> The USB polling interval is roughly 1 ms so I'd expect 1 ms peak offset, 1/2 
> ms if you average over enough samples.

It wasn't the polling interval as I just wrote in an update.

> Do you know about hanging bridges?  It's what you get when your sampling 
> clock beats against the clock behind the data source.  Averaging works if the 
> clocks are not in sync.  If the clocks are close to in-sync, then the offset 
> changes slowly so a batch of samples will get mostly the same offset.

Yes I know.


Btw, can you perhaps not break threading all the time when you answer to
the list?


Regards,
Achim.
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