on 7/31/00 9:33 AM, Henry B. Hotz at hotz@jpl.nasa.gov wrote:

> I have seen statements that the direct Open Firmware video support in
> 1.0.5 only has a single scan rate/pixel size that they support.  I
> have seen the vertical refresh rate quoted as 120 Hz and 60 Hz.

I've said this on the list in the past.  I got the numbers from the onscreen
frequency readout on my multisync monitor, so they're not definitive.

> Well I hooked up one of the really old (now anyway) Apple color
> monitors which are fixed frequency 35 KHz horizontal by 66 Hz
> vertical and it works just fine with OF, NetBSD, and X.  In fact it
> looks better than the nearly-as-old Apple 19 inch because it's
> crisper and the colors are more saturated.

Are you sure the old monitor isn't just more adaptable than you think?  I've
spent pretty much time trying different settings on one of those Mac->VGA
adapters with DIP switches and I've never seen the monitor sense lines make
a bit of difference in the video timing on /chaos/control.

> It makes sense that Apple would support their lowest common
> denominator scan rate in OF.  I don't have a PC monitor to try, but
> it's possible that there is something in the initialization code that
> checks for this monitor so they can do either VGA 640X480@60 or the
> Apple 640X480@66.  I can't see 120 Hz as a reasonable default and
> suspect that report was mistaken, or else my memory is.

120Hz is in fact _not_ a reasonable default.  There is a timing-related bug
in the Open Firmware driver for /chaos/control that causes it to fail to
properly initialize the video controller.  On my G3-upgraded machine, it
_usually_ comes up at 120Hz.  Repeated reboots will occasionally make it
come up in 60Hz sometime before I get sick of trying.

There exists an nvramrc patch that fixes this bug, written by someone who
worked at Apple once upon a time.  (This is where I learned that it was a
race condition.)  It was posted to a mailing list at some point, and
eventually made it into the Linux/PowerPC FAQ-O-Matic here:

http://www.dartmouth.edu/~jonh/lppc-serve/cache/378.html

Cheers,

-- monroe
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Monroe Williams                                         monroe@pobox.com