
Description of wmi810:

This utility has two functions:
The main function is to set a bit in an undocumented register in the built-in
graphics device of Intel's i810 chipset (GMCH). As a secondary function it
allows to change the Watermark and Burst-Length register in the same device.

The current i810 driver of the XFREE-Server 4.0.3 (and older) does not set
bit 2 of the undocumented GMCH register called MEM_MODE (MMADR+0x20DC).
If this bit is not set, noise and flicker will be seen on the screen (strength
of flicker depends on CPU activity, screen resolution, color depth and
miscellaneous H/V timings). Even with optimal settings of watermark and
burst-length, in some cases this flicker can only be partly reduced.
If bit 2 of MEM_MODE is set (# wmi810 -2s), the setting of watermark and
burst-length is not critical anymore and normally the default settings of
the i810 driver can be used.

Usage (call this utility after the X-Server has been started):

Step 1: Run wmi810 without any options.
If this shows that bit 2 of register MEM_MODE is set, someone (e.g. the
BIOS) has already set this bit and normally nothing more is to do.
If the table shows that bit 2 of MEM_MODE is cleared, continue with step 2.

Step 2: Run wmi810 -2s  This call should remove flicker in almost all cases.

Note that this utility is only a workaround. Long term the better way would
be to modify the XFREE i810 driver sources, but this should be done by the
maintainer of the i810 driver, not by EKF (hopefully the next XFREE version
of the i810 driver will have the necessary initialization included).

For questions and comments please mail to cr@ekf.de (Christoph Rabe)

EKF Elektronik GmbH, 59065 Hamm, Germany, Internet: www.ekf.de
2001-06-01
