Matrox G550 Xv on the second head

Ryan Underwood nemesis-lists at
Thu Sep 16 19:01:03 PDT 2004

On Thu, Sep 16, 2004 at 05:14:16PM -0700, Shaun Jackman wrote:
> Is Xv supported on the second head of the Matrox G550? I would like to
> use Xv with MythTV. If it is not yet supported, I'd like to lend my
> coding efforts. I'd appreciate a team-mate if anyone's interested. In
> any case, I'm not (yet) an Xorg hack. Where should I start?

It can be.  I don't remember if the BES (Back End Scaler) is used for Xv
or not, but it probably is, and the BES is only supported on CRTC1 (see
pg.588 of spec).  I'm not sure what the difference between this and
the xmga/mga_vid mplayer driver would be.  In any case, matrox has a
feature in the windows drivers called "DVDMax" which puts DVD video on
the second head, and probably with hardware YUV/scaling since the CPU
use is very low.  This is probably the CRTC2 "DVD Support" they are
referring to.  That could be a starting point for Xv support on the
second head, but I haven't researched it.

Something else you can do is to swap the CRTC<->DAC mapping.  I think
this can be done on all the G-series dualhead cards.  (On page 117 of
the manual, look at crtcdacsel.)  Problem here is that you need to
reprogram your DAC for the mode it's getting from the other CRTC.

Something _else_ you can do, which only only possible on G450/G550 is to
swap the DAC<->physical connector mapping.  I don't know how to do this,
but the BIOS parameter block sets a variable to tell the driver whether
the physical outputs are swapped.  This would happen i.e. on a card with
both a DVI and monitor port.  DacG can either output to panellink or to
VGA, and MGA-TVO can output to VGA or TV.  Usually DacG is on the first
head for the DVI output, and MGA-TVO is on the second head for
TV/secondary monitor output (since it is lesser quality).  But when a
monitor is only plugged into the 15-pin (secondary) connector at power
on and nothing on DVI, DacG output is mapped to the secondary connector
so that whatever is the primary display (in this case the VGA) gets the
better DAC.  When this is done a bit in the bios block is set and the
mga driver reads that to determine how to set things up.

Ryan Underwood, <nemesis at>
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