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My thoughts on the MB design...

To: riscy@pyramid.com (R3000 Mailing List)
Subject: My thoughts on the MB design...
From: paul@suite.sw.oz.au (Paul Antoine)
Date: Tue, 29 Jun 1993 09:35:34 +1000 (EST)
Organization: Softway Pty Ltd
Hello people,

This mailing list is the result of long trans-pacific telephone calls
between Neil and myself.  :-) Now that we've settled on a motherboard
as the basis for the design, and I've had a chance to listen to some
of the discussion, I'd like to outline some of my original design
thoughts...

CPU
        Neil's suggestion of using the R30x1E range is great - we can
        do the prototyping with the cheaper 3051 to prove the design,
        and do some of the initial porting, and then those who need
        the FPU can simply pop in a 3081, as they're pin compatible.

RAM
        Here's where I differ from most: my belief is that 8 or at
        most 16 SIMM sockets is plenty, as 16MB of memory will run
        things nicely, and 32 or 64MB would be enough for most people.

IO
        Neil's suggestion for the RAM/IO/DMA controller (3070??) means
        that implementing most of the IO is trivial (it provides 8 and
        16 bit busses for low-end IO chips).

        My original thoughts included putting single-chip ethernet and
        SCSI ports on the board, as these would give 32 bit IO in the
        critical areas, though I worry at being able to get them in
        something other than PQFP.

        The ISA bus could be used for floppy/serial/parallel, as these
        cards are plentiful and cheap, whereas a similar amount of 4
        or 6 layer motherboard space is expensive.

VIDEO
        The ISA expansion bus could readily be made VESA local bus,
        thus giving access to a very broad range of video cards, where
        the VLB versions give full 32 bit access and acceleration.

        As for the 34010: there is no way that we can compete on
        performance, price etc. for FAST video hardware with the
        mass-produced VGA/SVGA cards.

        I have no great objection to a SIMPLE video interface such as
        the DMA-driven one Neil mentioned, though I think most people
        have VGA/SVGA video cards they could (and would rather) use.

Keyboard
        This is probably best done with a 8041 microcontroller (or
        some other - what about a PIC?), as it reduces main CPU
        overhead.

Expansion
        As mentioned above, the main way of doing this is through the
        ISA/VESA bus, as it gives us access to sound cards,
        floppy/serial/parallel cards and a myriad others.

        There's also nothing stopping you putting space for a 'native R3000
        local bus' connector for those that want to design their own
        I/O cards of course [or those addicted to speed :-]

Paul

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Paul Antoine, Softway Pty Ltd                              Net: paul@sw.oz.au
PO Box 305, Strawberry Hills, NSW 2012, Australia          Tel: +61 2 698 2322
Level 2, 79 Myrtle St, Chippendale, NSW 2008, Australia    Fax: +61 2 699 9174

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