Re: Booting original iMac

["John D. Baker" <jdbaker%mylinuxisp.com@localhost>]

On Thu, 11 Mar 2010, Michael wrote:

> On Mar 11, 2010, at 3:39 PM, John D. Baker wrote:
>
> > The machfb attachment leaves the display garbaged, but booting completes

> Strange, I used to have access to a machine like that ( also with 6MB
> VRAM ) and machfb Just Worked. That was years ago though, around or
> before the 4.0 release.  The description ( garbage in the upper region
> of the screen ) sounds like something tried to switch to 24bit mode
> which makes no sense at all. Also, machfb isn't supposed to mess with
> video modes at all - guess I'll have a look at the code again.  On a

When machfb attaches, the bottom 3/4 of the screen is black.  The top
1/4 of the screen is fine alternating black/gray vertical stripes and
at the left side are jumbled mostly-white rectangular regions where
text would be drawn.  They scintillate such that you know it's still
working, but it's totally unreadable.  The image is otherwise stable.

> hunch - if you have a MacOS CD handy - could you switch the iMac to
> 800x600 and see if that changes anything? Also, is the picture stable

The internal disk (wd0) has a full MacOS X 10.3.9 installation on it.
When running MacOS X, I usually have it running 1024x768@75Hz in 24-bit
"millions of" colors mode.

I switched it to 800x600@95Hz (still in 24-bit color) and then
booted an unmolested GENERIC kernel.  There was no change in behavior.

Back in OS X, I switched it to 16-bit ("thousands of") colors mode.  In
this state, machfb text console worked properly.  I switched back to
1024x768@75Hz mode with 16-bit ("thousands of") colors mode.  machfb
text console works fine.

> when machfb messes up? If machfb does try to switch video modes it
> will probably use one of the standard modes, most of which don't work
> on the iMac's built in display. On the other hand, if it does try to
> switch modes it should use the firmware-provided EDID data.  Too bad
> I don't have that kind of machine around, machfb works fine on everything
> I have here :/

I hope the above information helps.  What else should I check, test,
probe or otherwise observe?

Is there any way to access the soft geometry controls for the CRT?
Mine's a bit off center and the extra bright right edge is annoying.
MacOS seems to apply such preference settings early in boot--I take it
they are stored with the display preferences?

More 5.0_STABLE and -current tests to come...

Thanks.

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