[ntp:questions] Can NTP sync within 1ms

Rob nomail at example.com
Tue Apr 29 08:41:55 UTC 2014

David Taylor <david-taylor at blueyonder.co.uk.invalid> wrote:
> For Rob, I would suggest that each TX have a GPS/PPS reference with sky 
> view, and that each PC was identical (e.g. all Raspberry Pi cards), and 
> then getting them synced to with 12 microseconds should be easy.  I 

Of course that is what we have.
E.g. on a prototype here at home:

ntpq -p
     remote           refid      st t when poll reach   delay   offset  jitter
oPPS(0)          .PPS.            0 l    2   16  377    0.000    0.000   0.000
xSHM(0)          .GPS.            0 l    1   16  377    0.000    7.682   0.152
*SHM(1)          .PPS.            0 l   16   16  377    0.000    0.008   0.001

PPS(0) is a PPS input from a professional GPSDO connected to a COM port,
SHM(1) is another GPS receiver interfaced via gpsd.  Just to see how
close they get and remain.

Not Raspberry Pi (yet) but normal PC systems, but I know it is possible
to get the system time within the desired 12 microseconds.

Unfortunately that is not the same as performing some task like outputting
audio at an accuracy of 12us, but that is the next challenge :-)

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