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Date: Sat, 21 Oct 95 22:04 WET DST
To: j@uriah.heep.sax.de, freebsd-current@FreeBSD.org
From: uhclem@nemesis.lonestar.org (Frank Durda IV)
Sent: Sat Oct 21 1995, 22:04:44 CDT
Subject: Re: clock running faster?
Cc: uhclem@nemesis.lonestar.org
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[3]As Frank Durda IV wrote:
[3]
[3]In fact, in this day of one-main-logic-board-fits-all, the processor clock
[3]is probably generated by a clock synth chip, ...

[4]joerg_wunsch@uriah.heep.sax.de spake:
[4]It is.  I've been installing one of these 66/90/100/133/.../180 MHz
[4]boards last week.  There are three jumpers encoding the CPU clock,
[4]next to a 14-pin chip (i forgot the numbers on it), next to the 14.318
[4]MHz crystal generator.

I rest my case.  That 14.31818MHz crystal is used to drive the 8254,
or whatever lies buried in the modern integrated system chip set
that pretends to be a 8254 (as far as command set and function goes,
but not necessarily in the timing department).

In addition to not being consistent in produced clock or accurate, the synth
clock may also be slowed-down deliberately as part of the EPA power
management stuff when the system is idle, thus slowing but not stopping
the CPU.  Some of this is done by the chipset and not the BIOS, particularly
in laptops, so FreeBSD would be affected.  However the 8254 continues running
on its rock-solid 14.31818MHz clock.

Frank Durda IV <uhclem@nemesis.lonestar.org>|"While we stand around arguing
or uhclem%nemesis@fw.ast.com (Fastest Route)| over what color the wheel should
...letni!rwsys!nemesis!uhclem               | be, Bill is getting richer."
...decvax!fw.ast.com!nemesis!uhclem         |