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VBE3TEST (Users)

posted by RayeR Homepage, CZ, 09.01.2009, 11:49

> Select use real VBE functions: no and then you can choose 4 basic CRTC
> feqs and then it will probe graphics mode from 56 to 100 Hz, use your
> monitor OSD to check real timing and report it here please.
In my case it doesn't work on 7900GT. I got very low refresh rates that caused monitor out of sync. I reported it to BW and here's reply:


I'll make a mistake. PCLK is really divided by 2. I''l try to understand how to control refresh-

For example I take this line -
> freq  |  25MHz  |  28MHz  |  ext1  |  ext2
> ------+---------+---------+--------+--------
> 76    |  blank  | BL-44Hz |   60   |   60
When using 76Hz *fake* refresh (and ext1/ext2 clocks), *fake* PCLK (i.e.
pixel clock, dot clock) is 48.905 MHz
divide it by 2, we get 24.453 MHz, it is our *real* PCLK When *real* PCLK is 24.453 MHz *real* Refresh is ~ 60 Hz (using GTF formula) as in your table.

It is strange that when *fake* refresh rate is increased,  *real* refresh is decreased.
If you try to lower or higher *fake* half-PCLK formula is somewhat broken.
So to get needed refresh you just have to try any possible refresh/resolutions and see what *real* result is.
If you need higher refresh just set higher resolution.

You also can use non-round refreshes like 79.45 Hz, to precisely control output PCLK.

It easy to understand using GTF table - www.vesa.org/Public/GTF/GTF_V1R1.xls

---
DOS gives me freedom to unlimited HW access.

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