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Re: MIPS R3000 - 2nd update

To: jeremy@sour.sw.oz.au (Jeremy Fitzhardinge)
Subject: Re: MIPS R3000 - 2nd update
From: caret@pyramid.com (Neil Russell)
Date: Wed, 23 Jun 93 14:34:41 PDT
Cc: riscy@pyramid.com
In-reply-to: <199306230917.AA05932@sour.sw.oz.au>; from "Jeremy Fitzhardinge" at Jun 23, 93 7:17 pm
> Neil Russell says on comp.os.linux:
> > *  I have decided that the IDT 79R3051E (the non FPU version) should be
> >    used.  Since getting good pricing is hard unless quantities are high
> >    I wish to stick to one type of CPU.  The board will be able to
> >    accommodate the IDT 79R3081E (with the FPU and more cache) if the
> >    user wishes to replace the CPU.  This would mean that full floating
> >    point support routines need to be written; ho-hum.
> I suspect the existing FPU emulator can form the core of a IEEE
> FPU emulator.  The hard part would be replacing the 387 front end
> with a mips one, assuming that the mips compiler uses a similar
> subset of IEEE FPU as the 386 one.  Since they are both gcc, this
> is probably the case.  Another guess: Mips FPU instructions are
> not going to be as hard to interpret as 387 ones.

FPU code is not that hard to write; I've done it before.  There seems to
be a fairly large amount of people wanting the FPU though.  That decision
doesn't need to be made until we do purchasing.

> > *  The R3000 is able to be a little endian or a big endian machine.
> >    Most operating systems that I've seen use the big endian mode, but
> >    since linux runs on the 386, little endian may be more appropriate.
> I don't know if it will make that much difference, but I suppose
> little-endian is easiest.  Big endian will probably make talking to
> ISA IO boards quite tricky.

I don't like the idea of hardware swapping the bits, so this favours
little endian, however, RISCos is big endian and has a few ISA bus
slots; so the software must swap the bytes itself; Mmmm, this is the
RISC way, after all...

Neil Russell            (The wizard from OZ)
Pyramid Technology                      Email:  caret@pyramid.com
3860 N. First Street                    Voice:  (408) 428-7302
San Jose, CA 95134-1702                   FAX:  (408) 428-8845


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