10 Aug
2012
10 Aug
'12
10:53 a.m.
-----Original Message-----
From: cctalk-bounces at classiccmp.org [mailto:cctalk-bounces at classiccmp.org]
On Behalf Of Al Kossow
Sent: Friday, August 10, 2012 1:11 PM
To: cctalk at classiccmp.org
Subject: Re: X Window server for NEC 7220
On 8/10/12 5:58 AM, Andrew Lynch wrote:
timing
Hi
Does anyone know of an X Window server implementation for the NEC 7220
GDC?
The chip has several names including the Intel
82720, NEC 7220A, NEC
7220D, uPD7220, uPD72020, etc. Essentially this graphics chip was the
main rival to the MC6845 prior to the domination of the IBM PC
architecture for microcomputers.
The 7220 and 6845 are quite different. The 6845 is pretty much just a generator, the 7220 is a microcoded graphics
processor. The problem you'll
have with putting a window system on a 7220 is the same one that SGI had
with the
68000 IRIS frame buffers. Neither is really designed for direct access to
the
framebuffer. Both assumed the graphics model was
geometry, and not
rasterops.
You'll be better off with some flavor of VGA (hopefully with an extended
flat
pixel addressing space) with the processor talking
directly to it, and not
try to
use an 80's era drawing processor.
--Al (been there, done that at AED with an AMD QPDM)
Hi Al! Thanks! Yes, the NEC uPD7220 has a fundamentally different approach
to graphics than the primitive MC6845 and derivatives (CGA, MGA, EGA, VGA,
SVGA, etc). However, implementing an SVGA on the S-100 bus is a non-trivial
exercise as well.
We've done three iterations of a CL GD542x based (QFP-160) SVGA
implementation prototypes that have gone essentially nowhere. Even
completely disregarding the builder assembly concerns of SMT and even
programmable logic devices -- even just finding a chipset that is compatible
with the S-100 bus has proven to be extremely difficult. We've resorted to
using the Propeller and even an FPGA (Spartan 3) based approach but none
provide the low level VGA compatibility or even a usable bitmap graphics
mode.
The NEC uPD7220 readily adapts itself to the S-100 bus and provides a nice
VGA monitor compatible bitmap. However it is completely non-VGA compatible
and really is as different from the MC6845 derivative as can possibly exist.
It uses a totally different approach down to the philosophical theory of
design!
If you or anyone else has some insight on how to implement a register
compatible SVGA on the S-100 bus I am very willing to listen! Thanks and
have a nice day!
Andrew Lynch