| Re: [chrony-users] Automotive usage of chronyd |
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On Sat, 4 Apr 2015, Bill Unruh wrote:
On Sat, 4 Apr 2015, Olivier Delbeke wrote:
.....
I made a first test in a near worst-case scenario : system without RTC and
without network,
but with only a USB GPS sensor (without PPS). Time/date after boot is Jan
1, 1970, 00:00:00.
I send the timestamps of the GPS sensor to chronyd (over a socket), but
chronyd rejects
them. Even if I use the first GPS timestamp to force the system time, the
subsequent
timestamps are still rejected by chronyd ("refclock sample not valid
age=-0.41" from
refclock.c - valid_sample_time())). What is the condition for a valid
sample ? I can
understand that samples are rejected, but the "< 0.0" conditions looks like
the drift is
only allowed in one direction. Is that right ?
Well, time does only flow in one direction. Why would the next sample be
earlier than the first from a GPS? GPS time is unidirectional.
I suppose what could be happening is that chrony is picking up the the first
report very late and that you have a time offset on the pulses, so the first
pulse time being read by chrony just before the next time comes in. It might
be an idea to discard the very first pulse time, and start with the second
one.
Thank you very much,
Olivier
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