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From: perry@sfsup.UUCP
Newsgroups: comp.sys.amiga
Subject: Re: Timing on A2000 vs 1000-add-ons
Message-ID: <1310@sfsup.UUCP>
Date: Fri, 10-Apr-87 12:30:57 EST
Article-I.D.: sfsup.1310
Posted: Fri Apr 10 12:30:57 1987
Date-Received: Sat, 11-Apr-87 21:24:48 EST
References: <18261@ucbvax.BERKELEY.EDU>
Organization: AT&T-IS, Summit N.J. USA
Lines: 36
Summary: Proper Buffering Is Key

In article <18261@ucbvax.BERKELEY.EDU>, schoet@ernie.Berkeley.EDU (Steve Schoettler) writes:
>    If worst case design of peripherals for the A1000 is so bad that
> manufacturers could only make 1 or 2 slot card cages, how is it that
> now so many vendors can offer 2000-and-1 boxes?
>    I can understand how a redesign of a circuit board and adding custom
> chips can give you more timing flexibility, but how can they do it to the
> A1000 without adding wait states?
>    I have ultimate faith in ASDG; if it can be done, they will do it.
> But why were we (at least I was) led to believe by so many hardware
> vendors in the past that it couldn't be done?

Proper (full spec) buffering allows a reasonably large number of expansion
slots to be placed in ONE  expansion  box. This is what the framers of the
Zorro spec envisioned from the start.

Current  slap-on-the-side-with-uh-oh-pass-thru products  DO  NOT  PROPERLY
buffer. You're  gonna  need proper  buffering to allow proper operation. A
slap-on-the-side-with-pass-thru  product  (if  one  existed which properly
buffered the bus) would squander  the  bus buffering on exactly one board.
This means downstream products  which would presumably also buffer the bus
would begin to  incur  wait  states (slots in a single card rack though do
not incur wait states  if  the containing card rack is the first card rack
in the chain - and - to my knowledge  no  one  seriously expects two fully
buffered card racks to be plugged into each other and work reliably.).

To sum up: Buffering  is essential.  Buffering more than once leads to wait
states downstream. Sots products do not buffer because they are inefficient
card racks (they contain only one  board) and to buffer properly would mean
wait  states  for  products  downstream. Card racks are more efficient card
racks (like that one?) in  that their bus buffering ammortizes over several
boards.

Also, thanks for the faith. You're right. If it can be done - we can do it.

Perry S. Kivolowitz
ASDG