[ntp:questions] Time server question

William Unruh unruh at invalid.ca
Tue Jun 25 18:35:18 UTC 2019

On 2019-06-25, Chris <xxx.syseng.yyy at gfsys.co.uk> wrote:
> Thanks again for the replies. Did a bit of digging this morning and
> find that the 1pps sync stuff has been done before. Well, many
> years ago in fact and more or less how I had visualised it - ntp
> data augmented by the 1 pps signal. Several pointers to the way
> forward and it's also supported in the FreeBSD kernel, using either a
> pin on a serial or parallel port for the 1 pps. Probably go for
> the parallel port, as that avoids the hardware to convert 1 pps
> ttl to rs232 levels.

Except most serial ports actually used on computers handle ttl levels
just fine.

> Have a Minix mini-itx box with two network ports which only draws
> about 12 watts. It has headers for the parallel and serial ports,
> so looks ideal to experiment with. Already has FreeBSD 11.2, but
> will reinstall 12 at minimum level to get the job done. Not after 
> perfection, but engineers always want the best result at minimum
> cost and timescales :-). A few uS should be more than good enough to
> maintain stratum 1 accuracy afaics, as network variables are

Stratum 1 says nothing about accuracy. You could have stratum 1 come off
smoke signals and have an accurcyof minutes, and a stratum 7 have an
accuracy of usec. All it indicates is how many steps the time server is
from a hardware time source. It says nothing about how good that time
source is, or how good the connection is between servers.

> orders of magnitude greater than that. Fun project anyway and
> will document once it's working...
> Chris

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