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Video subsystem...

To: riscy@pyramid.com (R3000 PC Mailing List)
Subject: Video subsystem...
From: Patrick Mackinlay <mackinla@cs.curtin.edu.au>
Date: Fri, 25 Jun 1993 22:47:52 +0800 (WST)
>[...comments from Drew about video bandwidth deleted...]
>This is a good point; this certainly points to using VRAM.  At present there
>are far too many unknowns about the video section to really address this
>issue.  Someone needs to do some research as to what cheap video stuff
>there is.  Using the S3 chip (as some one suggested) may be a good idea,

When I asked about S3 chips, I was told that they were all SMT with no
plans to do PGA or other packages. The other suggestion was to use the
6845 and the 3730's video stuff to do a very simple framebuffer solution.
As Drew points out, this would seem to suck up a lot of the available
memory bandwidth. There are a couple of other suggestions that might be
worth looking at. Firstly, to do the dumb framebuffer option, but use
VRAM. This would require a (relatively simple) bit of logic to clock
dots out of the VRAM at the right rate, and I don't think the 6845 is
capable of doing this.

The other option that I think has some merit is to use the TMS34010.
This chip used to be pretty expensive, but I think it's dropped a lot
since the last time I looked. The advantage with this chip is not so
much speed, but simplification of the overall design. Depending on
the price of the actual device, I think it could be one way to make
the video section pretty cheap. I've been told by some other guys
that it's quite easy to deal with as far as integration with the main
CPU is concerned (that's what it's designed for, after all!). I have
a few concerns that it might mean putting another ROM on the board,
but that might be cheaper and easier than other solutions (I think
it's got dynamic bus sizing stuff on-board in any case).

Any comments on this? Anyone have pricing info on the 34010?

BTW: There's a possibility the ET4000 or other VGA chips come in
non-SMT versions, but I'd personally prefer to stay away from them.
As far as I can see, the best way to slow a video system down is
to stuff it through a VGA chip...

Pat -- "There's only one thing left to do Mama, I got to ding a ding dang
        my dang a long ling long" (Jesus Built My Hotrod -- Ministry)
GCS d* -p+ c++ l++ m--- s+/- !g w- t- r


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