[time-nuts] Raspberry Pi NTP server

[Hal Murray]

stevesommarsntp at gmail.com said:
> I'd like to reduce the USB polling contribution by polling at 125
> microseconds as the Linux PPS folks suggest (http://linuxpps.org/doku.php/
> technical_information)    Would an FTDI-based USB convertor do the trick? 

It depends on which FTDI chip you use.  Both Prolific and FTDI make many 
chips.  The common ones are slow, polling at 1 ms.

The FT232R does poll at 125 microseconds.  I got mine on a breakout board from 
AdaFruit.  I also got a GPS chip on a breakout board to connect up to it.

Don't forget hanging bridges.  I don't know of any NTP software that knows 
about them.


jimlux at earthlink.net said:
> I would not expect another kind of USB to serial converter to do better.  The
> problem is higher up in the way that Linux handles USB devices.

I can't quite figure out what you are saying.  The USB rules say that the 
chips commonly used for serial ports get polled at 1 ms.  The FT232R says it 
goes faster and it works as expected at 125 microseconds.

Linux may have troubles with USB code, but I'm not sure how that impacts PPS 
processing.  The PPS timestamp is captured at interrupt time.  What else 
matters after that?


-- 
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