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From: John Baldwin <jhb@freebsd.org>
To: Alexey Dokuchaev <danfe@nsu.ru>
Subject: Re: System clock falls behind quickly on Mac mini G4
Date: Tue, 8 Apr 2014 10:41:44 -0400
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On Tuesday, April 08, 2014 10:29:29 am Alexey Dokuchaev wrote:
> On Mon, Apr 07, 2014 at 05:04:58PM -0400, John Baldwin wrote:
> > Also, if the frequency is calibrated incorrectly during boot for some reason,
> > your time-of-day clock will drift constantly.  I've seen this on x86 boxes
> 
> Yes, I remember a thread (x86ish) some time ago about bogus TSC calibration,
> but...
> 
> > where the TSC was calibrated incorrectly due to an interaction with SMM
> > interrupts for legacy USB emulation.  In that case, adjusting machdep.tsc_freq
> > to match the frequency from the CPU's brand string "fixed" the drift.
> 
> ... sysctl -a does not show machdep.tsc_freq for me on this G4 box for
> some reason (GENERIC kernel).

It wouldn't be tsc_freq on a powerpc box.  You'd need to see what your timecounter
is and what frequency it is using (kern.timecounter nodes) and see if that is
adjustable.

-- 
John Baldwin