Path: utzoo!attcan!uunet!unisoft!paul
From: paul@unisoft.UUCP (n)
Newsgroups: comp.arch
Subject: Re: The NeXT Problem
Message-ID: <1335@unisoft.UUCP>
Date: 19 Oct 88 16:36:04 GMT
References: <1249@cfa.cfa.harvard.EDU> <5025@cbmvax.UUCP>
Reply-To: paul@unisoft.UUCP (Paul Campbell)
Lines: 43

In article <5025@cbmvax.UUCP> daveh@cbmvax.UUCP (Dave Haynie) writes:
>Interrupt line to each slot.  Standard NuBus interrupts are weird; the board
>issuing the interrupt becomes the bus master and bangs on a chunk of memory
>that belongs to the board it wishes to interrupt.  This does make sense in
>a system of multiple masters, but not so much on something like a Mac II,
>where the motherboard CPU is basically the default master (though there is
>no real default master on NuBus).

Actually the problem is more the amount of board real-estate required to
make a board that is a master, you have to add a couple of extra state machines,
arbitration logic, drivers for the address lines etc etc it was really a
good idea to just provide a pin you yank low when you want to signal an
interrupt ..... my minimal slave logic is normally around 6 chips ...


>The NeXT machine changes the NuBus clock from 10MHz to 25MHz, and the bus
>drivers from Bipolar to CMOS.  That should be sufficient to render it
>incompatible with any existing NuBus cards.

yes I agree, if it weren't for this I think all my cards would run simply
by replacing the PALs with faster parts (and with more internal wait states -
isn't programmable logic great). Of course all the panel connectors would be
unreachable .....

Since it sounds like the minimal NeXTBus add-in card is going to have to
have 2 96 pin connectors it means that their sizes are going to be larger
at the bottom end (my cards are half cards - gets the prices way down)
plus they may be unmanageable if you put a tiny card in a deep slot.
Add to this the need for bus-master logic (NeXT's $25 chip -> $100 to
the consumer, I assume this chip contains the state machines but not the
drivers so add $5-10 more), and the faster interface (faster parts).
This will probably mean that the base prices of cards will be higher -
also since the volumes will be low for quite a while, I too don't expect
a mad rush of 3rd parties (from outside Higher Ed at least) designing
hardware for it.

		Paul

-- 
Paul Campbell, UniSoft Corp. 6121 Hollis, Emeryville, Ca ..ucbvax!unisoft!paul  
Nothing here represents the opinions of UniSoft or its employees (except me)
"Gorbachev is returning to the heritage of the great Lenin" - Ronald Reagan 1988
  (then the Wasington Post attacked RR [from the right] for being a Leninist)