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Index > DOS > How to directly access SVGA

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me239



Joined: 06 Jan 2011
Posts: 200
me239
Hello, I recently tried some SVGA programming, but I soon found how slow bank switching is with BIOS interrupts. Is there any way I can speak directly to the monitor port to switch banks? Thanks Smile
Post 24 Apr 2011, 05:55
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neville



Joined: 13 Jul 2008
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Location: New Zealand
neville
Yes I agree bank switching is very slow.

Not sure about direct register/port access, but if the video card supports linear frame buffering (LFB) that is the way to go. The LFB is mapped to the top of 32-bit memory space, and the video mode starts with 4 e.g. 4103h is mode 103 in LFB mode.

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Post 24 Apr 2011, 10:51
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me239



Joined: 06 Jan 2011
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me239
neville wrote:
Yes I agree bank switching is very slow.

Not sure about direct register/port access, but if the video card supports linear frame buffering (LFB) that is the way to go. The LFB is mapped to the top of 32-bit memory space, and the video mode starts with 4 e.g. 4103h is mode 103 in LFB mode.
Yes, but how do operating systems like Windows handle such fast graphics all in high resolution SVGA?
Post 25 Apr 2011, 00:15
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
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revolution
me239 wrote:
Yes, but how do operating systems like Windows handle such fast graphics all in high resolution SVGA?
With a driver specifically written for the card. Windows doesn't use the BIOS.
Post 25 Apr 2011, 01:56
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me239



Joined: 06 Jan 2011
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me239
revolution wrote:
me239 wrote:
Yes, but how do operating systems like Windows handle such fast graphics all in high resolution SVGA?
With a driver specifically written for the card. Windows doesn't use the BIOS.
But doesn't the BIOS speak directly to the driver? How could I pass the BIOS and go straight to the video card?
Post 25 Apr 2011, 02:18
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
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revolution
The BIOS does not "speak to the driver". The BIOS accesses the video card directly. A driver also accesses the video card directly. If you have a driver for your card then you don't need to use the BIOS.

If you have the specs for your card then you can access the card directly also. But the hard part is getting the full specs.
Post 25 Apr 2011, 02:32
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JohnFound



Joined: 16 Jun 2003
Posts: 3502
Location: Bulgaria
JohnFound
Every video card have some ROM that contains so called Video BIOS. The problem is that usually this video BIOS supports only very small amount of the cards features. The modern video cards supports it only for compatibility purposes. The full speed/features of the video card can be use only by some code, working directly with the hardware - i.e. driver.
However, the specifications for this hardware is often hard or impossible to be obtained. The manufacturers often release drivers only for Windows and recently for Linux.
Actually the tragedy of all new OSes is the lack of video drivers. This was a problem for Linux for many years. (now is more or less fixed).
Post 25 Apr 2011, 07:56
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vid
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Joined: 05 Sep 2003
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vid
Quote:
Every video card have some ROM that contains so called Video BIOS. The problem is that usually this video BIOS supports only very small amount of the cards features. The modern video cards supports it only for compatibility purposes.

Specifically for graphics during booting, and for Windows without proper driver installed (in such case it is quite common to use bank-switched mode).
Post 25 Apr 2011, 09:21
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