6. Known problems and limitations

There are several known problems or limitations related to the XFree86 ATI driver. They include:

• A number of system lockups and blank screens have been reported when using PCI Mach64 adapters. The great majority of these problems have been found to be due to system aspects that are unrelated to this driver. As of this writing, these problems can be divided into three general areas:

  Improper mouse protocol specification with some recent mice. Try different protocol specifications or another mouse.

  A system conflict with APM. This problem is Linux-specific. There is a bug in kernels 2.0.31 or earlier that prevents proper APM operation. Upgrade to a more recent kernel or disable APM support.

• When using a Mach64's accelerator CRTC, the virtual resolution must be less than 8192 pixels wide. The VGA CRTC further limits the virtual resolution width to less than 4096 pixels, or to less than 2048 pixels for adapters based on 18800's (with 256kB of memory) and on Mach64 integrated controllers. These are hardware limits that cannot be circumvented.
• Virtual resolutions requiring more than 1MB of video memory (256kB in the monochrome case) are not supported by the VGA CRTC on 88800GX and 88800CX adapters. This is a hardware limit that cannot be circumvented.
• Due to hardware limitations, doublescanned modes are not supported by the accelerator CRTC in 88800GX, 88800CX, 264CT and 264ET adapters.
• Monochrome interlaced modes are not supported on 18800-x and 28800-x when using a virtual resolution that is 2048 pixels or wider. This is yet another hardware limitation that cannot be circumvented.
• Video memory banking does not work in monochrome and 16-colour modes on 18800 and 18800-1 adapters. This appears to be another hardware limit, but this conclusion cannot be confirmed at this time. The driver's default behaviour in this case is to limit video memory to 256kB.
• The default mode does not work on the more recent Mach64 adapters. This problem is caused by the driver's attempt to use an incorrect dot clock for the mode. This will be fixed in a future release by reading the programmable clock generator's registers to determine the actual clock used by the mode.
• Most XFree86 servers assume that the video state on entry to the server is a text mode. This assumption is known to cause problems on operating systems which invoke the server from a graphics mode. DBCS versions of OS/2, primarily used in Asia, are examples of such operating systems. The solution, for now, is to somehow coerce the OS to invoke the server from a text mode. This driver has been changed to simply assume the mode on entry uses the adapter's VGA CRTC (in text or graphics modes). While this action alleviates the problem somewhat, it does not completely solve it, as the server could still be invoked from an accelerator mode. To properly fix this problem for all XFree86 servers is a large project, and will probably not get done anytime soon.
• Video memory corruption can still occur during mode switches on 18800 and 18800-1 adapters. Symptoms of this problem include garbled fonts on return to text mode, and various effects (snow, dashed lines, etc) on initial entry into a graphics mode. In the first case, the workaround is to use some other means of restoring the text font. On Linux, this can be accomplished with the kbd or svgalib packages. In the second case, xrefresh(1) will usually clean up the image. No solution to this problem is currently known.
• There is some controversy over what the maximum allowed clock frequency should be on 264xT and 3D Rage adapters. For now, clocks will, by default, be limited to 135MHz, 170MHz, 200MHz or 230MHz, depending on the specific controller. This limit can only be increased (up to a driver-calculated absolute maximum) through the DACSpeed specification in XF86Config. Be aware however that doing so is untested and might damage the adapter.
• Except as in the previous item, clocks are limited to 80MHz on most adapters, although many are capable of higher frequencies. This will be fixed in a future release.

• Mach32 accelerator's CRTC. This support is the first step towards accelerated support for Mach32's, Mach8's, 8514/A's and other clones.
• Colour depth greater than 8, where permitted by the hardware.
• Mach64, Mach32, Mach8 and 8514/A Draw Engines.
• Hardware cursors.