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From: daveh@cbmvax.commodore.com (Dave Haynie)
Newsgroups: comp.sys.amiga
Subject: Re: VME bus comments
Message-ID: <17639@cbmvax.commodore.com>
Date: 15 Jan 91 20:15:44 GMT
References: <17197@cbmvax.commodore.com> <2586@trlluna.trl.oz>
Reply-To: daveh@cbmvax.commodore.com (Dave Haynie)
Organization: Commodore, West Chester, PA
Lines: 45

In article <2586@trlluna.trl.oz> aduncan@rhea.trl.oz (Allan Duncan) writes:
>From article <17197@cbmvax.commodore.com>, by daveh@cbmvax.commodore.com (Dave Haynie):

>> And PCs have only recently grown 32 bit multiple mastered buses, while 
>> most VME systems have been doing that for some time. So sure, VME (and 
>> Multibus, etc) are more mature.  They pretty much have to be, at those 
>> prices.

>Not to forget that on the full blown VME systems there is the VMX (or
>whatever it is designated) to handle 32 bit local inter-board stuff, so
>that the VME bus is only being used for global transfers and I/O.  

There are actually a fair number of different mezzanine buses around, to 
support low cost add ons to VME and Multibus main boards.  These are a good
idea, because they help lower traffic on the main bus and make it much
cheaper to expand a VME system.  Though a good part of the reason for the
cost factors is that VME is expensive to implement, when compared to the
mezzanine buses.  In fact, lots of newer desktop machines out there, like the
Sun 4s and DECStations, have gone to high speed buses (S-Bus and Turbochannel,
in these cases) which are more in line with the mezzanine cost than something
like VME or Multibus.  Zorro II and Zorro III are, as well, much less complex
than a VME bus; its relatively easy to implement the bus connection portion of
the card with a few PALs and TTL chips.  To leave room for real work on the
[much larger] VME card, you have to use a dedicated VME controller chip these
days.

>_And_ the specs were worked out by the prospective vendors before they
>went to market, so it is free of mindsets, and most boards are compatible.

That's exactly what we did with Zorro III.  I wrote the specification before
any real hardware existed (I was developing the bus controller at the same
time), and both C= and the 3rd parties have to conform to the specs.  It's
always better to write everything down ahead of time, in one place, rather than
spread it all around (as we did for Zorro II, "well, you need this, and the
Motorola book, and it helps if you have schematics"), or just plain don't
say and let everyone guess, as in the case of IBM PC-AT bus (or its more
standardized "ISA" incarnation).

>Allan Duncan	ACSnet	a.duncan@trl.oz

-- 
Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests"
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	"Don't worry, 'bout a thing. 'Cause every little thing, 
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