[ntp:questions] u-blox reference clock driver

Terje Mathisen terje.mathisen at tmsw.no
Sat Aug 11 11:29:41 UTC 2018

David Taylor wrote:
> This was posted by lukas at fridolin.com on the NTP hackers list, just
> in case you missed it.
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Hi,
> I've been writing a reference driver for u-blox GPS receivers as
> part of my master's thesis and thought ntp hackers might be
> interested in it. Additionally to normal PPS operation this driver
> can make use of the u-blox's "Timemark" functionality.
> It does this by enabling the PPSAPI echo, which generates an echo
> pulse right after receiving a PPS pulse. This echo is connected to
> EXTINT0 on the u-blox, where it is timestamped. So now I have the PPS
> timestamp as a local time and the timemark as the receiver time to
> calculate an offset. The cool thing about this is, that the offset
> does not include the local interrupt latency anymore, which leads to
> less jitter.

This is indeed cool, do you have any graphs/stats for the 
actual/remaining jitter?


- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"

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