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From: gnu@hoptoad.uucp (John Gilmore)
Newsgroups: net.micro.68k
Subject: Re: SUN 3/160C question
Message-ID: <633@hoptoad.uucp>
Date: Tue, 18-Mar-86 03:56:59 EST
Article-I.D.: hoptoad.633
Posted: Tue Mar 18 03:56:59 1986
Date-Received: Fri, 21-Mar-86 04:23:40 EST
References: <7300003@uicsl>, <3358@sun.uucp> <6518@utzoo.UUCP>
Organization: Nebula Consultants in San Francisco
Lines: 30

In article <6518@utzoo.UUCP>, henry@utzoo.UUCP (Henry Spencer) writes:
> If the current software doesn't use it, be sure it works before you rely
> on it!  This may sound a bit silly, but it's not -- a friend of mine who
> worked with some of the very early commercial Suns discovered, as I recall,
> that the vertical-retrace interrupt on the Sun 1 (or maybe Sun 0.9) in fact
> did not work, and it turned out that Sun had never tried using it.

Actually, this is not quite true.  I diagnosed that problem.

The Sun-1 Multibus video board had a 3-bit field which specified the
interrupt level on which it was supposed to interrupt.  (A value of 000
would suppress the interrupt.)  It turns out that these bits were
inverted before being used as an interrupt level.  Thus a value of 000
specifies an interrupt on level 7, 001 is level 6, ... 111 suppresses
the interrupt.

This was discovered about 2 years after the product was in the field.
I discovered it because I noticed a software bug in the terminal
emulator which this hardware bug was masking.  At the time I
recommended that the "fix" be a documentation change; since only a few
customers were likely to be affected, there was no sense ECO-ing the
board.

I believe the diagnostics for the Sun-2 and Sun-3 color boards test the
video retrace interrupt.

Can we move further discussion (if any) to Sun-Spots (mod.computers.sun)?
-- 
John Gilmore  {sun,ptsfa,lll-crg,ihnp4}!hoptoad!gnu   jgilmore@lll-crg.arpa
			     Post no bills.