[time-nuts] Raspberry Pi NTP server

[Matthias Welwarsky]

On Freitag, 3. Juli 2020 19:44:48 CEST Hal Murray wrote:
> andrew.hancock at cyrus-consultants.co.uk said:
> > So I cannot use HaTs anymore, so I cobbled together a GPS ublox6 (same
> > module) but using a FT232RL, and connected all the pins correctly, and DCD
> > so I can get PPS.
> 
> FT232R is a USB chip.  Timing over USB is "interesting".  Do you know about
> hanging bridges?
> 
> Can you get a wire in to the GPIO pin the HAT used?  That would be an
> interesting experiment.
> 
> There may be a parameter you can tweak, but I can't think of the name right
> now.

Forgive me chiming in with a recommendation: Drop the Raspberry Pi and get a 
Beaglebone Black instead. It is the much better platform for timekeeping 
experiments.

Firstly, it has capture-mode timers that will give much more stable timestamps 
for the 1PPS kernel interface.

Secondly, you can drive these timers from an external clock source. That clock 
source can be a GPSDO. That means, you can hook up the timer input clock to 
the 10MHz GPSDO output and at the same time use it for timestamping the GPSDO 
1PPS pulses. Plus, this timer can be the "wall clock" for the Linux system, 
resulting in a zero-drift system time. Combine that with gpsd and you have a 
stratum-1 time source.

Thirdly, the ethernet mac is on chip and it supports hardware timestamps. This 
means, not only NTP but also PTPv2 is possible.

BR,
Matthias