Re: NetBSD as an NTP stratum 1 server

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Thu, Nov 16, 2023 at 11:21:03AM -0500, Greg Troxel wrote:
> If within 1s is good enough, NMEA only is ok.
> 
> If you have a system that is well-connected  and you set up NMEA you will
> find out that there are delays and that these vary by type of receiver.
> You use 'time1' in ntp.conf to adjust this.  I have 3 devices that need
> values of
>   0.116
>   0.0445
>   0.072
> to be close.
> 
> That is very coarse compared to 1 ms for PPS.  But indeed, if you have a
> machine that is not connected at all, it's really hard to tell it is a
> second off.
> 
> So basically you might think
>   NMEA only: 200 ms
>   USB PPS: 1 ms
>   gpio PPS: 100 us
> 
> and to do better (or to know you are doing better) you need to really
> pay attention.

To do better I think I'd go with an implementation of ntpd on a microcontroller
(maybe an ESP32, which has native ethernet) and use the PPS signal with a
capture channel. Doing true real time on more complex CPUs is really hard.

I know there is an implementation on arduino, but I think a 32 bit MCU
would be a better choice.

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--