By default, all the drivers set the AGP mode to 1X. To change this, use
the following in your XF86Config file:
Option "AGPMode" "n"
where "n" is one of "1", "2" or "4". If it used to work for you and now
doesn't, you may want to try manually setting AGP 2X (esp. for the
> AGPx2 can use lower signal levels if the graphics card asks for it,
> 1.5V instead of 3.3V (AGPx4 uses 1.5V high state always)
Wonder if this has anything to do with why some cards on some
motherboards work at some AGP multipliers but not others.