Subject: Re: NTP and PPS_SYNC option
To: john heasley <>
From: Simon Burge <>
List: tech-kern
Date: 12/16/2005 12:46:26
john heasley wrote:

> I do not think I fully understand the PPSAPI either.  Looking at com(4),
> and the RFC, it seems to exist for userland; to make PPS events available
> to userland and provide the ability to adjust PPS parameters, including
> which source (if any) calls hardpps().

That's as I understand it too.

Back to your original question, ntpd will use it to get pretty much the
exact time of the PPS signal instead of just relying on the "relatively"
approximate normal timestamp from the driver, and thus will be more
accurate.  Adding PPSAPI support shouldn't add to much to your driver.

> the clock on this particular MB is heinous.  A reboot usually looses at
> least a few seconds.  To the point that, in order to recover in any
> reasonable timeframe, we added a wrapper that takes the timestamp from
> the reference clock, calls settimeofday(), then starts ntpd.

Cute.  I wonder if you can get the same effect playing around with the
"burst" and/or "iburst" server keywords?

Simon Burge                            <>
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