On 12/07/2019 11:32, William Unruh wrote:
Do not use nmea as a time source. It it has a long delay ( hundreds of
ms) which depnds on the speed of connection, on length of the nmea
sentance, etc. EAch character takes from 100 of usec to ms to be
delivered, and the lengthof sentences is variable, and the gps sends out
a sentence only when it is not terribly busy ( which depends on how many
sattelites it is trying to handle, etc) It is good for setting the
seconds (sometimes-- if you ask it to send too many sentences it can be
out by more than a second totally messing up your timing).
One sentence (RMA) and a high baud rate make it useful for setting the
second.
I believe the OP is using it for seconds. The problem is, I think, that
ntpd will only use it, and only accept the PPS, if it is a true chimer.
Moreover, I think the OP's problem is that the NMEA timing is too
repeatable, so its root dispersion is too small to cover the static
error, although, if they had a lot of jitter, they would then advertise
a root dispersion that doesn't give credit to the PPS accuracy.
This is a degenerate case of root dispersion, as it is measured at the root.
Rather than setting as separate error bound for the NMEA, is there any
option to set a static offset separately for the NMEA.
_______________________________________________
questions mailing list
questions@lists.ntp.org
http://lists.ntp.org/listinfo/questions
