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Date: Fri, 20 Aug 2010 02:17:08 +0000
Message-ID: <AANLkTimNLAdPYQ0-yqyvR4YEuUsEG+mc7rFQ+WZUAvYh@mail.gmail.com>
From: "b. f." <bf1783@googlemail.com>
To: freebsd-hackers@FreeBSD.org
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Cc: phil hefferan <wdef200@gmail.com>, Phil Grundig <wdef200@yahoo.co.uk>
Subject: Re: How to read cmos clock - what is gettimeofday reading?
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>To further confuse matters there appears to be a common misconception on the web
>that the cmos time is automatically synced to system time on FreeBSD. This is
>incorrect: see msg03414 on freebsd-hardware at freebsd.org.

The situation has changed in 8-STABLE and 9-CURRENT since the above
message was written.  The timekeeping code was changed (by the person
who wrote the message that you cited) to periodically (every
machdep.rtc_save_period seconds) adjust the value of the rtc if ntp is
used to update the system time, machdep.disable_rtc_set=0, and the rtc
driver hasn't been disabled:

http://svnweb.freebsd.org/viewvc/base?view=revision&revision=207360
http://svnweb.freebsd.org/viewvc/base?view=revision&revision=208297

atrtc_{get,set}time, now in /usr/src/sys/x86/isa/atrtc.c, could serve
as a basis for your own code:

http://svn.freebsd.org/viewvc/base/head/sys/x86/isa/atrtc.c?view=markup

There are of course *_rtc_{get,set}time variants for other
architectures as well.

b.