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From: dave@murphy.UUCP (Lerxt)
Newsgroups: net.unix-wizards
Subject: Re: 4.2BSD and the VAX 11/780 clock
Message-ID: <110@houligan.UUCP>
Date: Fri, 17-Oct-86 09:11:07 EST
Article-I.D.: houligan.110
Posted: Fri Oct 17 09:11:07 1986
Date-Received: Sun, 26-Oct-86 02:06:30 EST
Organization: Gould Electronics, Ft. Lauderdale, Florida.
Lines: 31

In article <3723@umcp-cs.UUCP>, chris@umcp-cs.UUCP (Chris Torek) types:

>While the machine is running, the time is advanced by the interval
>counter.  The interval timer is set to interrupt every 10 ms. in
>4.2 and 4.3BSD; after 100 of these it bumps the seconds counter.
>It is possible (but unlikely) to keep the machine at a high IPL
>long enough that it misses a few ticks.  In this case the clock
>will slowly drift backward.

There's another little gotcha to this technique.  One time, we had a CPU
board in our 780 that went borderline and had to use the console clock-
margining feature (SET CLOCK SLOW) to slow down the CPU clock so that
the thing would run until Field Service could track down a replacement
board.  Unfortunately, the interval timer derives its frequency from the
CPU clock, so if you margin the clock, you time of day slows down or
speeds up correspondingly.  There were a lot of jokes that day about
the speed of work approaching c (or is it C?), and work dialation!

By the way, the same thing happens with VMS.

---
It's been said by many a wise philosopher that when you die and your soul
goes to its final resting place, it has to make a connection in Atlanta.

Dave Cornutt, Gould Computer Systems, Ft. Lauderdale, FL
UUCP:  ...{sun,pur-ee,brl-bmd}!gould!dcornutt
 or ...!ucf-cs!novavax!houligan!dcornutt
ARPA: wait a minute, I've almost got it...

"The opinions expressed herein are not necessarily those of my employer,
not necessarily mine, and probably not necessary."