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Re: MIPS R3000 - 2nd update

To: riscy@pyramid.com
Subject: Re: MIPS R3000 - 2nd update
From: caret@pyramid.com (Neil Russell)
Date: Wed, 23 Jun 93 14:50:34 PDT
In-reply-to: <199306231126.AA21307@nag.cs.Colorado.EDU>; from "Drew Eckhardt" at Jun 23, 93 5:26 am
> Software for the board, most noteably an X server and device 
> drivers.  If it doesn't run Linux and X, it's an expensive paper 
> weight.
> We need to set some finite time deadline for the board component
> specs (ie what chips, etc) so us software hackers can get started 
> writing SCSI drivers, VM code, etc that our code will be done and
> ready for debugging once the hardware is ready.

That is kind of difficult right now.  We still have no-one interested in
doing one of the harder tasks on the board, notable the ISA interface.
Once there are people allocated to all the tasks, the design shouldn't
take long.  I figure we a looking at about October for the first
batch of boards.

> Since this is a hardware project, we're free to wire 
> up the ISA bus so bytes on 16 bit transfers are automagically rearanged,
> and as long as you don't splat a short to an 8 bit address or an int
> to an 8 or 16 bit address and expect the bytes to come out in a given 
> order, there aren't any problems.

I'm not in favour of doing this kind of byte swapping.  If this issue
really matters, then we should definately run the OS in little
endian mode.  If the OS must run in big endian mode then the software
would have to byte swap for 16 bit accesses; this is the RISC way after
all...  BTW, to stop any possible mis-interpretations before they
start, the CPU must be placed in either big or little endian mode
when its reset.  It cannot be changed later.

> IMHO, software compatability should be a more important issue, ie 
> with commercial shrink wrap.  If people want to consider Ultrix 
> binary compatability, little endian SPIM is the only way to go. 
> If there's a SYSV MIPS ABI, we should comply with the endianness
> of that.


> I wouldn't be at all interested in a board that bore the burden
> of abysmal ISA video performance, since I want a *useable* 
> system that's more than a number cruncher.

Video, SCSI and ethernet are things that I'm not going to give up
on easily.

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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