[ntp:questions] Re: PPS working or not? FreeBSD 5.4

Per Hedeland per at hedeland.org
Mon Jan 30 07:03:36 UTC 2006

In article <qObDf.11636$wl.1818 at text.news.blueyonder.co.uk> "David J
<david-taylor at blueyonder.co.not-this-bit.nor-this-part.uk.invalid>
>Harlan Stenn wrote:
>>>>> In article <LY8Df.11489$wl.11104 at text.news.blueyonder.co.uk>,
>>>>> "David J Taylor"
>>>>> <david-taylor at blueyonder.co.not-this-bit.nor-this-part.uk.invalid>
>>>>> writes:
>> John> 5) [Make sure] you have "options PPS_SYNC" in your kernel config
>> David> 5 - I have not done that explicity.  How could I check that,
>> and David> change it if required?  It's been 10+ years since I ran
>> UNIX.
>> Assuming an x86 box, put the following in /usr/src/sys/i386/conf/PPS:
>Many thanks, Harlan.  I'll look into this, although I am a little 
>disappointed to find that less than 24 hours after starting with FreeBSD 
>I'm having to recompile the kernel!

Well, using PPS_SYNC shouldn't be *required* to use the PPS signal on
FreeBSD - what it does is make the kernel discipline the local clock
directly from the PPS signal, but FreeBSD also supports the PPSAPI, to
let ntpd collect the timestamps from the PPS signal. It should be
possible to use this via the ATOM driver. I haven't personally verified
any of this though (hence the "should"s) - and I guess PPS_SYNC may give
better results, but it could be interesting to try both variants.

--Per Hedeland
per at hedeland.org

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