From: roell@informatik.tu-muenchen.de (Thomas Roell) Subject: Re: X1.1 and ET4000 card Date: 9 Jul 1992 07:01:52 GMT
>Well, I think I have to add my own 0.02$. The latest SVGA cards have more
>than 8 clocks. They get the other clocks by doubleing some of them. I
>think this is done by another register. So the old X386 server did
>not handle this register correctly, so that you always have the
>doubled clocks. This was fixed by the 'vendor "hiclock"' patch.
>Now the new X386 server should handle the additional clocks right.
>I hope my explainations are right. (correct me if not)
That's not completely correctly. First the vendors now use by default
only 8 different dotclocks. They use the doulble clocks in HW, but
enable a bit that divides them by 2 for normal modes (i.e. CS0 is
50MHz, then divided by 2 to get the 25MHz normally used for 640x480).
The reason why this special handling wasn't in X386 before is simple.
The databook of the Et4000 stated that you have to use the divide by
two bit only in mode where the HW dotclock is over 45MHz and then use
it in conjuction with another one, that adjustes the sequencer
acordingly. This description is wrong according to what vendors are
doing now. They use this divide by two bit as general dot-clock
pre-divide.
- Thomas