[ntp:questions] Time server question

Miroslav Lichvar mlichvar at redhat.com
Wed Jul 24 11:58:54 UTC 2019

On Wed, Jul 24, 2019 at 12:44:26PM +0200, Mike Cook wrote:
> > Le 24 juil. 2019 à 11:19, William Unruh <unruh at invalid.ca> a écrit :
> >> 
> >> The hardware under consideration can time the pulse arrivals more
> >> precisely than the interrupt delivery time, thanks to special hardware.
> That tickled a grey cell. There was/is a timing product family
> bc635/637 time and frequency processors sold by Microsemi which can
> timestamp a PPS input event  to 100ns resolution.  Various OS drivers
> are available, but no ntp refclock driver AFAIK. 

There may be cheaper and better options for a highly accurate NTP server
today. For example, the I210 NIC supports HW timestamping and has SDP
pins which can timestamp PPS. The same device/clock is timestamping
packets and pulses, so there are no asymmetries due to PCIe, etc. This
is supported in existing software. Timestamps in NTP packets can have
sub-100ns accuracy. In this case it would make sense to apply the
corrections from GPS, but I'm not sure how it would be implemented.

(I'm responding to the newsgroup as messages from the mailing list are
not forwarded back. People asking questions in the newsgroup may want to
check the archives of the list to see if anyone responded there.)

Miroslav Lichvar

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