Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!cbmvax!daveh
From: daveh@cbmvax.commodore.com (Dave Haynie)
Newsgroups: comp.sys.amiga
Subject: Re: Additional CPUs (was: A rough future for the Amiga???)
Message-ID: <10802@cbmvax.commodore.com>
Date: 11 Apr 90 19:28:56 GMT
References: <16192@snow-white.udel.EDU> <1990Apr8.013940.12984@wam.umd.edu> <10715@cbmvax.commodore.com> <19543@grebyn.com> <1990Apr10.163745.16255@wam.umd.edu> <14895@s.ms.uky.edu> <19594@grebyn.com>
Reply-To: daveh@cbmvax (Dave Haynie)
Organization: Commodore, West Chester, PA
Lines: 34

In article <19594@grebyn.com> ckp@grebyn.UUCP (Checkpoint Technologies) writes:
>In article <14895@s.ms.uky.edu> sam@ms.uky.edu (Michael W. Mills) writes:
>>ddev@wam.umd.edu (Don DeVoe) writes:

>But the A2091 no longer has a Z80 CPU.  It seems that when ST506 was
>dropped, the added CPU cost more than it was worth and took too much
>space on a board that also had to hold 2 meg RAM and a disk drive.

Basically, with ST-506 out of the way (which is a dumb interface, not much
different than a floppy disk interface), there was no longer any need for
an intelligent IOP on the hard disk interface.  The custom DMAC chip on
the 2091 does the job much better than a general purpose CPU would.  SCSI
drives are intelligent as well, and they basically do the rest of the job the 
2090's Z-80 was doing.

I think you tend to find things moving in circles with respect to I/O 
processing.  Step one is to have the CPU do most of the work, basically
using real dumb I/O ports.  The next step is to build an smarter I/O
chip, something that'll handle the low-level protocols and just hand the
CPU cooked bytes or words, possibly even via DMA.  One step further and
you add a dedicated I/OP to deal with the I/O chips.  But with the 
dedicated IOP, you may find you can get away with real dumb ports once
again.  With enough work, though, the general purpose I/OP can be replaced
with a real smart chip that does the job far better.  At least until the
next generation of I/OP arrives.  Etc.

All of which doesn't really matter than much.  The important part is to
have the solution, whether dumb I/O, smart I/O, or I/OP, match the problem
you're trying to solve.

-- 
Dave Haynie Commodore-Amiga (Systems Engineering) "The Crew That Never Rests"
   {uunet|pyramid|rutgers}!cbmvax!daveh      PLINK: hazy     BIX: hazy
                    Too much of everything is just enough