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From: rbharding@trillium.uwaterloo.ca (Ron Harding)
Newsgroups: comp.sys.amiga.hardware
Subject: IBM cards in the Amiga
Message-ID: <1990Jul20.172301.6908@watdragon.waterloo.edu>
Date: 20 Jul 90 17:23:01 GMT
Sender: daemon@watdragon.waterloo.edu (Owner of Many System Processes)
Distribution: comp
Organization: University of Waterloo
Lines: 69


    My roommate and I have access to free Nestar Arcnet cards for the IBM
PC.  We will both be getting Amiga 3000s very soon (my first Amiga, he's
replacing his 1000).  We have been considering possible ways to use the
Nestar cards in the Amigas.

    We don't consider the Bridgeboard an acceptable option.  It's too
expensive, and who wants an 8086-based MS-DOS machine, anyway?  If CBM
made a 286- or 386-based board with at least EGA graphics, things might
be different...

    What we are thinking of is a bus-adapter board which uses the
Bridgeboard slot to connect the IBM slots to the Zorro bus.  The primary
function of this board would be to map the IBM bus's 1Meg memory space
into one of the many unused Megs of the Zorro address range.  It would 
also have to map the IBM's 64K io space into another Zorro range.  Which 
ranges of the Zorro space are used could be set by switches, or maybe even
Autoconfig.

    We have not resolved some issues yet.  Unfortunately, the Amiga Hardware
Reference does not describe either Zorro or the 1000's expansion slot
($%#^#%@%#!!).  The issues we are concerned about are:

    - The IBM bus provides 6 or so interrupt request lines.  We're pretty
      sure that it would not be hard to use switches to map the IBM's 6 IRQ
      (or at least the ones that are in use) lines to some unused Zorro 
      interrupt request lines.

    - The IBM bus provides 3 DMA channels.  Is it possible to map these to
      Amiga DMA channels just like the interrupts?  DMA is not essential
      for most IBM cards anyway, but wouldn't hurt.

    - Many cards for the IBM PC are very slow.  The Nestar is probably one
      of them.  In fact, some original PC cards are so slow that they won't
      even work in an AT, since the shortsighted designers of them didn't
      give the option to generate wait-states.  Newer IBM network cards have
      a jumper to specify the number of wait-states they need.  You set the
      jumper if you have a 33 Mhz 386.  You don't need it for your 4.77Mhz
      PC.  It would be quite desirable to have the real old, slow cards
      without wait-state jumpers work, since they are cheap.  We don't plan
      on using any hard-disk controller boards, so blazing performance is not
      a concern.  It should be acceptable to have the bus-adapter
      automatically throw some switch-selectable number of wait-states into
      every IBM bus access.

    - Any IBM cards we will be concerned with are 8-bit.  The 68030 seems to
      have special instructions for dealing with 8-bit peripherals ( the
      MOVEP instruction, for example).  I don't remember offhand whether or
      not the IBM slots in the 2000 or 3000 are 16-bit long-slots or not.  If
      so, then there may be special challenges.  I seem to recall that IBM
      long-slots allow bus-mastering.  Not something I want to deal with...

    Just imagine the possibilities if this is do-able!  There are quadrillions
of cards for the IBM PC in the world.  There are only a handful of Zorro
cards.  With this card, you could have internal modem cards, fax modems,
extra video cards (VGA or whatever), any network card (Ethernet, Token-
ring, Arcnet, etc), A/Ds and D/As.  All sorts of stuff.  You'd have to be a
hacker-extraordinaire to get a lot of it working, but then you are reading
this newsgroup, aren't you?

    This is getting a bit long.  Has anyone out there considered the
challenges of this?  If you've already built such a beast, we'd love to hear
about it.  On the other hand, if you know of some reason why it's not
possible, well, who asked ya, anyway?

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Ron Harding                      | Nuke'Em:  Get them before they get you!
rbharding@trillium.uwaterloo.edu | Another quality home game from Butler Bros
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