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From: jon@msunix.UUCP
Newsgroups: net.arch,net.micro.68k
Subject: CSA 68020 piggyback board
Message-ID: <236@msunix.UUCP>
Date: Sat, 28-Jun-86 04:14:14 EDT
Article-I.D.: msunix.236
Posted: Sat Jun 28 04:14:14 1986
Date-Received: Tue, 1-Jul-86 04:11:32 EDT
Organization: Via Visuals Inc.
Lines: 38
Keywords: Anyone using one?
Xref: watmath net.arch:3626 net.micro.68k:1713

Now for an entirely different subject...

Today our directory of hardware plopped a CSA 68020 piggyback board
on my desk and asked me to play with it a bit to see if it would
work in our system (a Via Visuals Design Center).  For those of you
who have never seen one of these (the CSA board, I'm sure none of you
have seen a Via Visuals Design Center), it is a 3" by 4" pc board with
an 020, an 881, a few resistors and caps, and three PALs on it, which you
can plug into a 68010 socket.  I suppose the PALs have all the logic
to generate the DSACKs, etc for the 020.

I plugged it in and tried out the PROM diagnostics which seemed to work
fine.  When I tried booting it loaded UNIX off the disk fine, initialized
okay, then hung, probably when creating process 1, init.  I only spent
about a half hour with it, so I can't be sure how far it got, although
I do know the 020 tri-stated its bus, and the DMA chip (Motorola) had
the bus and was waiting for the disk controller to acknowledge.  This
was quickie "let's try it before we leave" hack, there were many things
suspect, i.e. excessive capacitance from 14" board extenders, etc.

The main difference I would guess is the difference in the exception
stack for bus errors and address errors.  The interpretation of the
bits in the special status word, and the location of the offending
addresses is different on an 010 and an 020.  This really shouldn't
be a problem yet, as I'm not worried about getting virtual memory
to work yet, although I did modify the bus error exception handler
to work with the 020s two different exception stacks.  Supposedly
everything else should be ok.

So, if anyone is using one of these and has any advice, I would
appreciate hearing from you, or if you've had any problems, I'd
like to hear about them.  I'll probably work a day or two more on
it to see what happens.  We see it mainly as an easy way to get an
881 on board.  When I get it working, I'll post my findings on
the whole matter.


"If we did it like everyone else,	  Jonathan Hue
what would distinguish us from		  Via Visuals Inc.
every other company in Silicon Valley?"	  sun!sunncal\
						      >!leadsv!msunix!jon
"A profit?"				amdcad!cae780/