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Linux - Embedded & Single-board computer This forum is for the discussion of Linux on both embedded devices and single-board computers (such as the Raspberry Pi, BeagleBoard and PandaBoard). Discussions involving Arduino, plug computers and other micro-controller like devices are also welcome.

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Old 08-02-2011, 10:25 AM   #1
onirepap
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Modify video signals output


Hello,

This is my first post so i hope to not write in the wrong place.
I have a PC104 board with a vortex86sx processor and a XGI volari Z9s video controller, the SO is a very stripped down version of linux with just busybox and less more provided by the makers of the PC104 board, the bootloader is Syslinux.

Beside the VGA output there is an output for flat panel TFT display, but I have trouble to use a TFT because the video signal looks blocked on a fixed resolution (too high for my panel) and i can't change them.
My display is 480x272 but if i can't have this resolution i can use an higher one and waste some pixels.

If i put vga=ask in the syslinux.cfg and select different modes the aspect ratio changes but the timings are the same.
I tried to change the resolution and the timings with the command "fbset" using the options -g and -t (using the displays optimized timigs), but it didn't changed nothing. It looks it can change the resolution (if i choose a VESA mode) but without changing the timings i only have a corrupted signal even on VGA output because it would have a refresh rate too fast.
I tried also to change only the pixclock parameter (fbset -pixclock 100000) but it didn't changed anything in the output...

Do you have any suggestion?

Thanks,
Franco

Last edited by onirepap; 08-02-2011 at 10:37 AM.
 
Old 08-02-2011, 11:04 AM   #2
business_kid
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vga=ask on the kernel boot line would be nice. There's also vga=nomodeset, or nofb, or normal
It's probably framebuffer or vesa, and they can be adjusted. If it uses X, the setup there can be set.

Tell us a bit about what you find in there. Don't leave us guessing.
 
Old 08-02-2011, 05:10 PM   #3
onirepap
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Right, I'm sorry for the lack of infos but i forgot to write them.

My linux uses linux kernel 2.6.29 and it's CLI only. It uses the framebuffer (i have /dev/fb0) and there isn't X.
During the boot it looks that something called XGIfb set the video mode.

When i put vga=ask i have only few video modes, 4 text modes and some graphics modes (320x200, 320x240, 640x400, 640x480, each with some differents depth). Anyway, whatever option i choose, the pixel clock and the horizontal sync and the vertical sync are always the same. (and I want to lower the freq of the first two, at least)

I don't know what else you may need to know because i'm relatively new to Linux World, so ask whatever you need.
 
Old 08-03-2011, 02:39 AM   #4
business_kid
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No, that's all good.
I set up a framebuffer 10 years+ back. There was a config file /etc/??/fb.conf (guessing wildly)

cd /etc && find -name 'fb.conf'

Go looking for that and see if there's anything in it you can fart about with to improve things.
I would also try (without spaces in between)
vga=xxx,nomodeset
vga=xxx,nofb

where xxx is your chosen mode for the panel

Last edited by business_kid; 08-03-2011 at 02:40 AM.
 
Old 08-03-2011, 01:58 PM   #5
onirepap
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I searched but there is no fb.conf, I've read somewhere that there could be a fb.modes but i don't have that, too...
Should I create them?
Tomorrow morning I'll try those options in the kernel boot line and I let you know.
 
Old 08-04-2011, 02:47 AM   #6
business_kid
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ATM, I'm still slugging coffee to wake up, but my memory of framebuffer 12 years or so back was that it did vesa modes. If that's so, you can certainly slow your hsync & vsync. That said, the refresh must be very fast or else your chosen panel is a piece of xxxx. fb.modes sounds fine for a config file.

fb.modes file
 
Old 08-04-2011, 03:26 PM   #7
onirepap
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I tried that file but it didn't worked... I found some more documentation about my board and i found that there is a different BIOS for each of the supported TFT panels. So i just have to change it. I tried and it in fact changed. But it looks to me an extreme way to change resolution! Maybe i'll try to see if it's possible to access the video's BIOS and override this option in software.

Thank you for your support, even if my case is different, i still learned something new from you!
 
  


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