Multiple screens.

Leif Delgass ldelgass at
Fri Apr 8 08:38:42 PDT 2005

On Apr 4, 2005 4:13 PM, Peter Ankerstål <uchman at> wrote:
> On Mon, 4 Apr 2005 17:05:38 -0400
> Alex Deucher <alexdeucher at> wrote:
> > On Apr 4, 2005 4:53 PM, Peter Ankerstål <uchman at> wrote:
> > >
> > > >
> > > > Yes, crtc1 is driving both displays.  both the LCD and the VGA port
> > > > are getting the same mode, probably 1024x768 at 60hz.  If you want to run
> > > > the LCD at say 1024x768 at 60hz and the VGA port at say 1280x1024 at 75hz,
> > > > you will need to program both crtcs (crt/display controllers); one for
> > > > each output.  if you just want to use one crtc to drive either the vga
> > > > port or the lcd, there's not really an easy way to use modes beyond
> > > > the capabilites of the attached monitors after X is started.
> > > >
> > > If i start two x-sessions I can run one on each screen. The one i run in
> > > 1024x768 Is on both screens because both screens support it. And the other session
> > > runs 1280x1024 And is only displayed on the external screen. (1280x1024 is not
> > > supported by the internal screen).
> > > It must be a way to do this but with only one x-session.
> > >
> >
> > the only way to do simultaneous 1280x1024 on the vga port and 1024x768
> > on the LCD is with 2 crtcs.  the chip supports that, but the driver
> > does not.  one thing you could try is to start X on the vga port at
> > 1280x1024 and then use xrandr or cntl-alt-+/- to switch the mode to
> > 1024x768 and then use the bios fn key combination to switch the
> > display to the vga port and the lcd port, be careful though to make
> > sure you are using a 1024x768 mode that your lcd can handle (probably
> > 60Hz). YMMV...
> >
> > Alex
> >
> I've tried that. But it doesnt work at all. :/.
> --
> Peter Ankerstål.
> _______________________________________________
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> xorg at

Display switching through the bios is disabled by default for mach64
in current releases. There is a private option to enable it, I believe it is:

Option "BiosDisplay" "yes"

However, since my TV-out patch was merged into cvs, bios display 
switching will be on by default for x86, since it is needed for TV-out.

Note that the TV-out feature as implemented currently and display 
switching through the bios in general is potentially dangerous, since
it is overriding the normal driver code to set modes (through the card
registers) with calls to the card bios.  The driver's view of card state 
can become inconsistent with the mode programmed by the bios.
Although I haven't heard any examples of this causing problems, the
normal checks of the capabilities of the displays are bypassed.

Both for TV-out and clone/dual-head, it would be better to program the
crtcs directly through the registers as Alex said.  For TV-out, I'm not 
sure if all the relevant information is available to do this on mach64.

Leif Delgass

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