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Date: Tue, 11 Jun 1996 09:55:37 +1000
From: Bruce Evans <bde@zeta.org.au>
Message-Id: <199606102355.JAA01251@godzilla.zeta.org.au>
To: current@freebsd.org, nate@sri.MT.net
Subject: Re: CLOCK stuff at bootup
Sender: owner-current@freebsd.org
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>OK, I didn't pay alot of attention when this stuff went in because I was
>scared away from current.  However, after the glowing reports from the

Pay attention or read old mail.

>However, I'm not sure what I'm supposed to be doing re: the clock
>messages now.

>FreeBSD 2.2-CURRENT #2: Mon Jun 10 12:46:29 MDT 1996
>    root@nec.sri.MT.net:/usr/src/sys/compile/CARD
>Calibrating clock(s) relative to mc146818A clock ... i586 clock: 75171042 Hz, i8
>254 clock: 1193196 Hz
>CLK_USE_I8254_CALIBRATION not specified - using default frequency
>CLK_USE_I586_CALIBRATION not specified - using old calibration method
>i586 clock: 0 Hz
>CPU: Pentium (75.16-MHz 586-class CPU)
>  Origin = "GenuineIntel"  Id = 0x524  Stepping=4
>  Features=0x1bf<FPU,VME,DE,PSE,TSC,MSR,MCE,CX8>

>I'm assuming I'm supposed to define one or both of the above, but why?

Because defining one or both might work better.  Using sysctl to set the
actual (current) value might work better still.

>How do I determine which one is the more accurate, since obviously the
>i854 clock is not running at the same frequency as my Pentium chip. :)

The i8254 clock determines long term accuracy.  Run for a while and
determine the drift and/or the time daemon adjustments.  Use sysctl to
specify the i8254 clock frequency that minimizes the drift and/or the
adjustments or accept the default from calibration or accept the fixed
default.

The i586 clock determines intra-clock-interrupt times.  Specify the i586
clock frequency that minimizes the jitter in getttimeofday().

Bruce