[ros-bugs] [Bug 2239] Strange problem depending on the used monitor

[ReactOS.Bugzilla at www.reactos.org]

http://www.reactos.org/bugzilla/show_bug.cgi?id=2239





------- Comment #5 from mail at colinfinck.de  2007-08-02 14:47 CET -------
This problem is probably related to the fact that different controller unit
numbers (ChildIndex in the videoprt/vbemp code) were introduced in version 1.1
of the VESA DDC standard (see http://www.vesa.org/public/VBE/VBEDDC11.PDF).
Therefore older monitors might simply ignore the controller unit number and
always return the EDID data. This is why our function for reading the EDID
never fails.

Most-probably our code for reading the EDID data is not wrong as I also tested
reading the EDID with the DOS application "get-edid". It also returns valid
EDID data for every controller unit number I input, when my 17-inch monitor is
plugged in.

I also tested if we really need the VBEReadEdid function for reading the EDID:
When I disabled this function and only enabled VBEReadEdidUsingSCI, the call
never succeeded using my 17-inch monitor.
But I also tested get-edid with some newer monitors (20-inch and 22-inch
widescreen TFTs connected over DVI) and the EDID call without using I2C never
succeeds here. Probably these monitors only support reading the EDID over I2C
(although I did not test ROS with them).

>From that I conclude that both functions are really necessary and VBEReadEdid
needs to be fixed.


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