Re: [chrony-dev] Wake from sleep on OS X

[Bill Unruh <unruh@xxxxxxxxxxxxxx>]

On Wed, 2 Dec 2015, Bryan Christianson wrote:

> > On 2/12/2015, at 10:40 AM, Bill Unruh <unruh@xxxxxxxxxxxxxx> wrote:
> >
> >
> >
> > William G. Unruh   |  Canadian Institute for|     Tel: +1(604)822-3273
> > Physics&Astronomy  |     Advanced Research  |     Fax: +1(604)822-5324
> > UBC, Vancouver,BC  |   Program in Cosmology |     unruh@xxxxxxxxxxxxxx
> > Canada V6T 1Z1     |      and Gravity       |  www.theory.physics.ubc.ca/
> >
> > On Wed, 2 Dec 2015, Bryan Christianson wrote:
> > > As for keeping the RTC clock in sync, ntpd appears to do this by calling settimeofday() each time it updates its stats files.
> > >
> > > I can add a scheduled event in the Mac OS X driver to call settimeofday() at regular intervals to force the RTC update. I would think an update every 15 minutes would not be too expensive.
> >
> > One of the features of chrony is that it can keep track of the rtc and its
> > rate difference from 1 and its offset and use that information next time the
> > rtc is used. However, if you keep resetting the rtc, that does not work. Thus if you switch your computer off for 3 days, this would allow chrony to
> > compensate for the rate difference of the rtc clock from unity (ie 1 sec/sec) There is a problem with this in that the rate depends on tempreture, and the
> > tempurature when the rate of the rtc is detrmined ( while the computer is
> > running) and rate when it is off and cold can be different by a few PPM (eg
> > second per month). The natural rtc rate can be off by up to 100PPM (seconds
> > per day) Thus if you keep resetting the rtc (eg if you have the kernel's
> > resetting of the rtc every 11 min) you do not have the rate correction. If you
> > have the rate correction, the rtc can be out by many seconds. I do not know if
> > the OSX kenel has that 11 min mode that the linux kernel has. chrony
> > deliberately disables that mode on linux so it can measure the rtc clock drift
> > rate.
>
> I didn't know that - thanks.
>
> In light of that, I am not sure how the RTC should be synchronised. As far as I can tell there is no equivalent to hwclock to force synchronisation and that it is dependent on the user either setting the time manually or running ntpd

I have no idea how OSx timekeeping works. However clearly there is a way of
setting the rtc and setting the system clock. hwclock is simply a package
which does those things on Linux as a user runnable program. I also do not
know what the difference is between "setting the time manually" and "run
hwclock". hwclock is how a user sets the clock, either the system clock from
rtc or rtc from the system clock, under linux. What is the procedure on OSx?
Anyway as you can see I am way out of my depth here.


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