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 Post subject: [Solved] Intel graphics framebuffer glitch
PostPosted: Wed Jan 27, 2021 6:20 am 
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I am experimenting with display mode setting for Intel integrated graphics and I am having some trouble. I am able to switch between different display modes (like 640x400@70, 640x480@60, 1024x768@60, etc.) but some pixel columns seem to be glitched, no matter which display mode is being used. Attachments show what the problem is. It's almost like pixel stream doesn't match with frame timings. BTW. Im testing on G31 (GMA 3100) chipset but I only have documentation for G35 (GMA X3500).


Attachments:
File comment: This is what I expect
expected.png
expected.png [ 830 Bytes | Viewed 127 times ]
File comment: This is what I get
shifted.png
shifted.png [ 844 Bytes | Viewed 127 times ]

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Last edited by pvc on Wed Jan 27, 2021 2:59 pm, edited 1 time in total.
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 Post subject: Re: Intel graphics framebuffer glitch
PostPosted: Wed Jan 27, 2021 2:59 pm 
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I can't believe it took me this long to find it.

Turns out that I did not mask low bits of GMADR register when reading it from PCI config space. Instead 0xE0000000 I used 0xE0000008 address as graphics memory base. Last 8 looked so similar to other 0s on the screen in VGA font. I did see it only after setting up serial connection (and whole CLI) to the machine and using some semi-decent font in terminal emulator.

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 Post subject: Re: [Solved] Intel graphics framebuffer glitch
PostPosted: Wed Jan 27, 2021 4:02 pm 
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Hehe... Yeah it has happened to me in the past. Frustrating.

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 Post subject: Re: [Solved] Intel graphics framebuffer glitch
PostPosted: Wed Jan 27, 2021 7:23 pm 
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Remote login of one sort or another is extremely useful when developing window systems.

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