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Re: Vesa bus.

To: riscy@pyramid.com
Subject: Re: Vesa bus.
From: tim@ubitrex.mb.ca (Tim Braun)
Date: Fri, 2 Jul 93 10:51:29 CDT
> From ronald%csunix.urc.kun.nl@kunrc1.urc.kun.nl Fri Jul  2 04:46:52 1993
> Date: Fri, 2 Jul 1993 11:41:42 +0200 (CET)

> > Date: Thu, 1 Jul 93 22:00:17 +0200
> > From: wolff@zen.et.tudelft.nl (Rogier Wolff)
> > 
> > There seems to be a discussion going about adding a "Vesa bus".
> > Is this the "Vesa local bus" that current 486 machines are 
> > equipped with? If so, I thought that this bus was more or less
> > exactly the 486 bus interface. Therefore, adding somthing compatible
> > with this on another processor would be hard.
> > 
> > Please correct me if I am wrong.....
> > 
> >                                     Roger.
> > 
> I don't know this, but I read somewhere a couple of weeks ago (sorry I don't
> know where) that VESA local bus is going to end. Why?: Dell computers
> was one of the originators of this standard, but recently they seem to 
> have announced to only support PCI (an intel bus for x86). Well how does
> this affect VESA Local bus? Dell sent a letter to other VESA local bus 
> manufacturers, claiming that by using VESA local bus technology they
> infringe on DELL patents. This way Dell wants VESA local bus to die a 
> soft death. Maybe they're pushed by Intel in doing this, wasn't Intel
> the corporation who started all the legal wars recently?? 
> I'm sorry I don't remember where I read this (I read too much lately), but
> can anyone confirm this, if so it might be not so smart to use the VESA bus
> on this project.
> Ronald Schalk

The PC industry silicone providers are definitely moving to PCI and away from 
VESA.  The reasons are:
 - processor independence.  Intel is selling/licensing PCI to everyone.
   They want you to use PCI for P5/Pentium.  DEC wants you to use PCI for
   Alpha (so they can leverage the silicone that will be developed to
   PCI).  MIPS wants you to use PCI for some decendent of r4400pc.  VESA
   is indeed very 386/486 specific.
 - bus features.  VESA has little IRQ/DMA support.  It's designed for video
   interfaces, not i/o.  Only one interrupt level is on the Local Bus.
   PCI is designed as an interface bus.
 - bus bandwidth.  VESA is 32 bits wide (max).  Some of the above processors
   use 64 bit data buses.  PCI supports 64 bit transfers.  This is (basically)
   what gives PCI twice the bandwidth of VESA.  (~200 MBytes/sec vs. ~ 100).

'93 was the year of VESA because it's:
 - available now.
 - does give full processor bandwidth access to video.  (Video performance.)
 - allows the planar video memory configuration to '386 designs. (Video 
   performance again.)
 - relatively cheap.  (Profit performance.)

Dell wanted to claim a licensing fee from VESA for their connector.  (EETimes)
That kind of legal hassle will indeed help PCI.  Both PCI and VESA ask fees for
copies of their spec's.

I don't think this project should use either bus.  Put a simple frame buffer
on the board, and put an (some?) ISA slot(s?) on.  The licensing issues
are likely to slow such a decentralized project down too much.

Tim Braun                          |
Ubitrex Corporation                | Voice: 204-942-2992 ext 228
1900-155 Carlton St                | FAX:   204-942-3001
Winnipeg, Manitoba, Canada R3C 3H8 | Email: tim@ubitrex.mb.ca


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