From: daveh@cbmvax.commodore.com (Dave Haynie)
Newsgroups: comp.sys.amiga.misc
Subject: Re: Problems with the A4000
Date: 14 Sep 92 17:48:50 GMT
Reply-To: daveh@cbmvax.commodore.com (Dave Haynie)
Organization: Commodore, West Chester, PA

In article <1992Sep12.083819.17967@news.iastate.edu> barrett@iastate.edu (Marc N Barrett) writes:

>   The problem comes down to the architecture of the A4000 itself.  As has been
>rumored before, several good systems were canceled not long after DevCon '91,
>a year ago.  What has not been said is that these included all of the systems
>that Dave Haynie designed that incorporated the AA chipset.  Indeed, none of
>the new Amiga systems -- including the A4000 -- were designed by him.  They
>were designed in a rush by junior engineers at Commodore.  

As usual, Mark is, to put it bluntly, talking out of his ass here.  

There was ONE system discussed at DevCon, something called I called the A3000+.
It, like the A4000, was based on the A3000 system architecture and the AA 
chips.  I had some other goodies put in there, and I had hoped that this would
go on as a production machine, but it was just a development platform.  We
did development with it, then moved onto real production.  The A4000 is the
first fruit of that development effort.

The A4000 project was headed by Greg Berlin, the other half of the main A3000
engineering team.  Greg is the only hardware designer who's been here longer 
than I have, by about six months.  I was heavily involved in the A4000 design
in the "AA" and Expansion subsystems.  No, it wasn't a full-time job for me,
basically because most of this had been prefected already, and Greg had two
junior guys and one other senior guy (Scott Schaeffer, who did the '040 module)
helping out on day-to-day debugging, etc.  Which is just the way I wanted it --
I started working on "AA" stuff back in the fall of '90, and by the time the
A4000 project started I was moving onto other things.

>   The whole design of the A4000 can be summed up in a fairly short sentence:
>the A4000 is an A3000 with the CPU moved to a card, the AA chipset kludged in,
>and with the SCSI subsystem replaced with IDE.  

The AA chipset is hardly "kludged" in.  The form of the AA chipset is something
me, Greg, and the AA people (Bob Raible and Bill Thomas) discussed at length
back before there was an AA.  It was designed to drop fairly easily into an
A3000-class machine, much like ECS did.  Actually, the A4000 design is 
considerably cleaned up over my A3000+ prototype, in that Greg's people did a
new gate array, Bridgette, which manages much of the system's datapaths more
efficiently than the 9 or so TTL buffers the A3000+ used to do the same job.

Again, Mark, why do you always post stuff you have absolutely no knowledge 
about?  Especially things like the genesis of the A4000 and AA, a subject upon
which only a very few people could produce a real authoritative post.

>Basically, the A3000 was not designed for the AA chipset.

Correct.  In point of fact, the AA chipset was designed for the A3000, as I
explained above.

>The Ramsey and Buster chips in the A3000 were designed for use with the ECS,
>in particular the 2M Agnus chip.  

The RAMSEY and Buster chips have ABSOLUTELY nothing to do with managing the 
chip bus.  

Gary and a couple of PALs manage the chip bus in both the A3000 and A4000.
The signals from Gary are very generic, they work as well with AA as they do
with ECS.  Most of the control for a particular chip set comes from the chip
bus controller, Alice in AA, Agnus in ECS.  Gary just provides a few chip
selects and a bit of buffer control logic (eg, it's basically controlling
the CPU gating on and off the Chip bus, which is real simple).

>The new Alice chip in the AA chipset -- the replacement for Agnus -- can 
>potentially address 4M of chip RAM.  

No it can't.

>   OK, I've established that the A4000 is an A3000 with the AA chipset kludged
>in.  Now it makes sense to me that it would have cost less in development costs
>to simply leave the A3000's SCSI design there instead of removing it and
>replacing it with something else.  The costs of including SCSI in the A4000,
>then, would have been practically zero in development costs.  

The inclusion of IDE cost a few months of Joe Augenbraun's time.  Joe was a 
junior engineer working for Greg (he left C= a little while back to go invent
HDTV in Princeton or some-such).  Say what you will about IDE's inability to
address lots of cool devices, I'll agree.  But it cost practically nothing to
develop, it's a very, very simple interface.  And it costs very little to
build, it's basically a PAL and a couple TTL buffers, not a full controller
like SCSI.  IDE was designed to be nearly free to add back when the PClone
industry whipped it up.

>   In addition to the costs involved in removing the SCSI subsystem from the
>A4000's design, 

We're now having to pay to remove SCSI from the A4000!?!  Buy yourself a 
clue, man!

>The new design was created by Randall Jessup, and includes extra hardware to
>make the IDE interface and HD look somewhat like a SCSI interface and HD to
>Amiga software.  

Randell did do the software.  Far as I know, it's pretty much the same in both
A600 and A4000, and in both cases, the IDE driver pretends to be a SCSI device,
since most hard disk utilities know how to deal with SCSI devices.  A good idea
IMHO, no really big deal.

>In the short-term, then, the prices on the A4000 and other new systems will 
>be higher than if they had used a SCSI design. 

Not on your life.  You obviously know nothing about computer development to
come up with this conclusion (not that anyone here had any doubts in the first
place).  I'll make up some numbers just to give you your first lesson (eg, I
don't know what these things cost, but we'll ballpark it).  Let's say that 
SCSI cost $25 per system, IDE $2 per system.  Let's say that Randell and Augi
each spent 3 months on IDE.  I don't know what Randell and Augi made, but I
guess around $25,000 would cover the two of them for three months (better than
cover them, since they're doing other things at the same time).

So how many machines to I need to make to cover the costs of IDE development.
The differential here is $23, I need to make $25,000.  So I'm making a profit
on this change, all else being equal, on machine number 1087.  Again, these
are made up numbers, I suspect that the IDE stuff is actually paid for much
sooner, since most of Randell's work was already done for the A600.

-- 
Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests"
   {uunet|pyramid|rutgers}!cbmvax!daveh      BIX: hazy
	"Work like a horse, drink like a fish"	- Psychefunkapus