Re: Graphic options for DS10L

Dave Froble wrote:
John Santos wrote:

JF Mezei wrote:

Is there some "big picture" document that described how the OS interacts
with a graphics card ?

FredK mentioned that VMS for instance is likely to use 32 bits and use
the last 8 bits for special stuff like alpha value.

Does the OS really have any control over how the graphics card behaves,
or does the graphics card have a variety of options and the OS chooses
one or the other ?

Another example: From what I have read, VMS does not enable/support the
DVI output of the Radeon 7500. Wouldn't it be a simple case of VMS
depositing a couple of values in a register and making an interrupt so
that the graphics cards turns on the DVI port ?

Or would VMS truly have to provide data in a very different way to the
graphics card in order for the DVI output to ne enabled ?


And if VMS lacks the feature that enables the DVI port, is there
anything preventing a privileged user from accessing the graphics card
directly and making the interrupts/data transfer necessary to turn a
port on or off (DVI, or the composite video output) ?


I think that commodity (PCI, intended for an X86 PX) graphics cards
are not only stranger than you imagine they are stranger than you
(the generic "you", i.e. everybody, not you personally) *can* imagine,
to steal from Arthur Eddington or JBS Haldane or someone. (I once
did a web search on this quote, and it was very confusing. I think
several people were quoting each other, and it wasn't clear who said
it first.)

I think Fred K has mentioned that they have ROM-based (or EPROM-based,
to allow for firmware upgrades) X86 code on them, which you have to
trigger to get various results. So the boot loaders/SRM/Graphics
initialization programs for Alpha, I64, etc. have to have a primitive
X86 emulator in them in order to initialize the cards! Or you need
to hand-decode the initialization ROM routines for a given card and
figure out what bits/bytes/registers to poke in what sequence and with
what kind of timing to get the card running. I imagine what portion
of the X86 instruction set each card might use is different, depending
on manufacturer, model, rev level, and is completely undocumented.

I also vaguely recall Fred saying that the DVI interface didn't
work because he needed to discover the right magic command sequence
to enable it. Perhaps since then he has done so, since it now seems
to be working for Bart.

I think this is why they stick to such a limited set of cards. Wouldn't
other proprietary, non-X86 O/S'es have the same set of problems? (I.E.
Solaris Sparc, HP-UX, IBM, Apple OS X, etc. etc.) Do Linux and BSD
running on X86 support many PCI graphics cards that they don't support
on non-X86 architectures? (Because on X86, they can probably just
execute the onboard ROM rather than trying to figure out what it does
and emulate it, making the creation of an X86 Linux driver much easier
than the creation of a PowerPC or Sparc Linux driver, for example.)
The vast hoards of open-source Linux driver developers would have a
much easier time making a new graphics card work on an X86 than elsewhere
(but still not trivial.)

I bet sound cards have the same set of issues.


John, you realize what you're doing, don't you? That was a 5 gallon can of gas thrown onto the "port VMS to x86" demand.


:-) And it will probably turn out that I am completely wrong about all
this, but that doesn't make the slightest difference... :-) :-)


--
John Santos
Evans Griffiths & Hart, Inc.
781-861-0670 ext 539

.

Relevant Pages

  • Re: Graphic options for DS10L
    ... Does the OS really have any control over how the graphics card behaves, ... From what I have read, VMS does not enable/support the ... DVI output of the Radeon 7500. ... and somehow tell the X server to also resize the screen ...
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  • Re: Graphic options for DS10L
    ... Does the OS really have any control over how the graphics card behaves, ... From what I have read, VMS does not enable/support the ... DVI output of the Radeon 7500. ... X86 emulator in them in order to initialize the cards! ...
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