The base support in the Mach32 X server is for 8 bpp, with a dot clock of up to 80 MHz. At present 15/16 bpp is supported on only three of the many RAMDACs; however those three cover the most commonly sold cards.
RAMDAC Max Dot Clock BPP Max Resolution Video RAM Required -------- ------------- --- -------------- ------------------ Default 80MHz 8 1280x1024i 2Mb Default 80MHz 8 1024x768 1Mb ATI68875 135MHz 8 1280x1024 2Mb ATI68875 80MHz 16 1024x768 2Mb AT&T20C49x 80MHz 8 1024x768 1Mb AT&T20C49x 40MHz 16 800x600 2Mb BT481 80MHz 8 1024x768 1Mb BT481 40MHz 16 800x600 2Mb
The RAMDAC is reported when you run the Mach32 X server with the
"-probeonly" command line option, or can be specified in the
XF86Config file.
The ATI68875 (or the TLC34075) is used on the Graphics Ultra + and the Graphics Ultra Pro. The Brooktree 481 is used on most Graphics Wonder cards. The AT&T20C491 is used on many of the OEM cards that are built into component systems.
The BIOS detection unfortunately lumps the BT481 and the AT&T20C49x together, while they require different configuration controls in 16 bit mode. SuperProbe can tell the difference, and will report which it finds. In the server itself, the BT481 is considered the default value. If you have an AT&TC49x RAMDAC on your card you will have to include the Ramdac entry in the XF86Config file as below.