Path: utzoo!mnetor!uunet!cbmvax!daveh
From: daveh@cbmvax.UUCP (Dave Haynie)
Newsgroups: comp.sys.m68k
Subject: Re: NuBus advantages/disadvantages?
Message-ID: <3522@cbmvax.UUCP>
Date: 24 Mar 88 22:02:15 GMT
References: <2669@tekigm2.TEK.COM>
Organization: Commodore Technology, West Chester, PA
Lines: 27

in article <2669@tekigm2.TEK.COM>, klieb@tekigm2.TEK.COM (Kurt Liebezeit) says:
> Keywords: NuBus

> I am curious why someone would label Apple's implementation of the NuBUS
> as crap. From what little I have read about the NuBUS it seems to make sense:
> the assertion/sampling edges would appear to eliminate hold time problems,
> and I like the way that the bus decides on cycle N who has control during
> cycle N+1. What are the serious shortcomings of the NuBUS? The only thing
> that I didn't care for was the fact that the Mac II NuBUS has no DMA; cards
> are expected to supply their own.

The idea of the way NuBus clocks things is really elegant.  The problem is
that it's slow; some 3 or so wait states for the 68020 in the Mac II.  Last
I checked, 3 added wait states means that all NuBus access has you '020
running at half it's potential speed.  And the one way around this, the
nybble burst mode, isn't supported by Apple.  It was nice of Apple to add
an interrupt to it, but I still have problems with it.  

That's not to say Apple won't be successful with it, they didn't do so
poorly with the Apple II bus, which was neither fast nor elegant.

> Kurt Liebezeit
> tektronix!tekigm2!klieb
-- 
Dave Haynie  "The B2000 Guy"     Commodore-Amiga  "The Crew That Never Rests"
   {ihnp4|uunet|rutgers}!cbmvax!daveh      PLINK: D-DAVE H     BIX: hazy
		"I can't relax, 'cause I'm a Boinger!"