BootX enhancement request

Benjamin Herrenschmidt bh40 at
Wed Aug 25 04:21:52 EST 1999

On Tue, Aug 24, 1999, David A. Gatwood <dgatwood at> wrote:

>That's not _entirely_ true.  The hardware itself relies on the nvram
>setting in order to determine the initial startup mode before it starts
>loading MacOS.  That's why you can do tricks with newer versions of MacOS
>like have the preferences set to 1024x768 and the pram/nvram set to
>640x480 and have it switch half-way into booting. (Makes it nice for
>MkLinux on x100's where you have to be in 8-bit color, but don't want to
>run MacOS that way.)  The Monitors & Sound CP does set the nvram value, at
>least on some machines, unless it changed quite recently, but you
>sometimes have to delete its prefs files to convince it to do so.

Yes, you are right. But the fact remains that video drivers are free to
store this in any proprietary format they want and I had some trouble
getting this to work with iMacs and blue G3s. Also, this nvram setting is
limited to those "official" mode values, but the driver is free to
implement completely different modes, and there's also some support for
DCC slowly appearing in MacOS. I don't think we can rely reliably on this
nvram value.

What I could eventually do is to add code to BootX that asks the driver
about the current mode (the driver should be able to return me all sorts
of informations, including some, but not all, of the timings) and build a
kernel command line with those. We should find something generic since
I'm not sure I can easily find out which kind of driver to use on the
command line (atyfb, platinumfb, controlfb, ...)

I have plans to extend BootX so that i can also setup OF environement
variables for quik-based booting. It would be able to setup those infos
there too. I'll look into this as soon as I have a new hard drive for my
8500 (the old one joined my pile of dead HDs last week, I'll soon be able
to make some kind of modern art with all those HDs ;-).

           Perso. e-mail: <mailto:bh40 at>
           Work   e-mail: <mailto:benh at>
BenH.      Web   : <>

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