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Re: XZ

To: matomira@acm.org (Fernando D. Mato Mira)
Subject: Re: XZ
From: kyriazis@sgi.com (George Kyriazis)
Date: Mon, 19 Oct 1998 12:53:40 -0700 (PDT)
Cc: linux@cthulhu.engr.sgi.com
In-reply-to: <199810190644.IAA17078@link.csem.ch> from "Fernando D. Mato Mira" at "Oct 19, 98 08:44:45 am"
Reply-to: kyriazis@sgi.com
Sender: owner-linux@cthulhu.engr.sgi.com
In a previous episode, Fernando D. Mato Mira claimed:
> At 05:15 PM 10/18/98 -0700, you wrote:
> >    XZ is one of the variants of the Elan/Extreme series of cards,
> >which have one or more geometry engines on the card.  The geometry
> >engines need microcode downloaded for full functionality, and the
> >interfaces are not externally documented, so it is hard to build
> >linux support without access to the IRIX source for reference.
> 
> What about just getting the console running (no X server)?
> How do GR2 (Indigo Elan) and GR3 (Indigo II Elan) differ in terms of
> programming?
> 
I did some asking around.  Here's what I found:

* In order to do anything, you have to download microcode.

* The monitor PROM downloads a mini-microcode that could be used.  I am
  not sure what the entry points look like to the PROM.  I think this
  is the safest bet.

* The full-functioning microcode (that does 3d) is downloaded at boot
  time before the X server initializes.
 
* The people that I asked are not clear about the programming differences
  between GR2 and GR3.  Certainly they are the same for OpenGL-level
  programming.  My guess is that there are differences in the CPU interfacing
  and video back end.  User-level code is the same, but kernel initialization
  and management code may be different.

* Getting things up and running on a GR-type (Express) architecture is 
  definetely more difficult than Newport.

* Documentation will be hard to find.  Documentation for programming the
  microcoded engines, even harder.  You could, of course, use the existing
  microcode.

  --george
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