ATI Adapters README file
: Known problems and limitations
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7. Known problems and limitations
There are several known problems or limitations related to the XFree86 ATI
driver.
They include:
- 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-x'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.
- The ``VScan'' modeline parameter is only supported when using the VGA
CRTC.
- Interlaced modes are not supported on 18800-x and 28800-x adapters when
using a virtual resolution that is 2048 pixels or wider.
When using a 18800-x with 256kB of video memory in 256-colour modes, this limit
is reduced to 1024.
This is yet another hardware limitation that cannot be circumvented.
- Video memory banking does not work in monochrome and 16-colour modes on
18800-x 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.
- Video memory corruption can still occur during mode switches on 18800-x
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 complete solution to this problem is currently known.
It appears this corruption occurs due to either video memory bandwidth or
RAMDAC limitations, and so the driver will limit mode clocks to 40MHz.
- 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 80MHz, 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 items, clocks are limited to 80MHz on most
adapters, although many are capable of higher frequencies.
This will eventually be fixed in a future release.
- The use of a laptop's hot-keys to switch displays while this driver is
active can cause lockups and/or other woes, and is therefore not recommended.
It is not currently possible to solve this problem.
- In situations where the driver is to simultaneously display on both a
panel and a CRT, the same image will be seen on both.
In particular, this means the CRT must be able to synchronise with the timings
of the panel's native resolution.
This is quite evident when the panel has ``odd-ball'' dimensions, such as
1400x1050, a resolution not commonly possible on CRTs or projection
equipment.
Also, the display of independent images on the panel and CRT is not currently
implemented, and might never be, pending resolution of the previous item.
Support for the following will be added in a future release:
- Mach32's accelerator 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 on non-integrated controllers, where
permitted by the hardware.
- Mach32, Mach8 and 8514/A Draw Engines.
- Hardware cursors where implemented by hardware.
This has already been done for Mach64 integrated controllers.
- TVOut, i.e. the ability to use a television screen as a monitor.
- Motion Video, i.e. displaying an asynchronous data stream (TV signal,
DVD, etc.) in a window or full-screen.
- 3D operations.
ATI Adapters README file
: Known problems and limitations
Previous: Video modes
Next: Reporting problems
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