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Old 01-29-04, 08:23 PM   #3
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Join Date: Jan 2004
Location: Louisville KY
Posts: 10
Default I tried it

I'd never heard of pixel clock before you mentioned it. Thank you.

I find two definitions, one in NVLinuxNotes4191.pdf which says

RefreshRate = PixelClock / ( VertFrameLength * HorizFrameLength)

[goes on to note "The VertFrameLength refers to actual frame length and not simply the visible resolution". (p 84).]

Assuming VertFrameLength equals visible verticle resolution, and PixelClock=215, I should be able to get a 2048x1536x24@68Hz. Not bad!

Only thing is, the other definition, courtesy of the XFree86 Modeline Generator at disagrees and demands 2048x1536x24@45Hz. I'm not sure why they're different, does anyone know why?

Anyhow, I went with the Xfree Modeline generator because it was more conservative, and because it generated cut'n'pastable configuration for XF86Config:
Modeline "1664x1248@64" 215.00 1664 1696 2512 2544 1248 1273 1286 1311
Modeline "1792x1344@56" 215.00 1792 1824 2640 2672 1344 1371 1384 1412

However, X doesn't deign to use these, putting this message in the verbose log:

(WW) NVIDIA(0): Not using mode "1792x1344@56":
(WW) NVIDIA(0): horizontal sync width (2640 - 1824 = 816) greater than 256
(WW) NVIDIA(0): Not using mode "1664x1248@64":
(WW) NVIDIA(0): horizontal sync width (2512 - 1696 = 816) greater than 256

Grr... in other words there are some constraints that this video mode calculator doesn't take into account. I have to invest more time to grok what they are.
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