From aa8vb@ipass.net Sun Sep 26 13:45:46 1999
Date: Sun, 26 Sep 1999 13:45:46 -0400
From: Randall Hopper <aa8vb@ipass.net>
To: XFree86@XFree86.org
Subject: 3.3.4 - Matrox G200 DGA extension errors
Message-ID: <19990926134546.A9054@ipass.net>
References: <19990926133904.A8749@ipass.net>
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      XFREE : 3.3.4
      CARD  : Matrox Millenium G200SD PCI 16Meg
      SERVER: mga
      OS    : FreeBSD 3.2-RELEASE

I tested out 3.3.4 with respect to DGA returning the correct address of
the linear frame buffer.

Using this utility:
     http://www.ipass.net/~dbhopper/aa8vb/fxtv/dgafbtest.c

I found:

  16bpp  - Works fine

  24bpp  - In 1024x768, works fine only if desktop is 1024x768. 
           But if desktop size is other, the base frame buffer (0,0 pixel)
           address returned by XF86DGAGetVideoLL is incorrect.
           
           For example, in 1024x768 with a 1600x1280 desktop, 4032 bytes
           need to be added to the returned base address to obtain the
           correct address of the 0,0 pixel.

  32bpp  - In 1024x768, works fine only if desktop is 1024x768. 
           But if desktop size is other, the base frame buffer (0,0 pixel)
           address returned by XF86DGAGetVideoLL is incorrect.

           For example, in 1024x768 with a 1600x1280 desktop, 2304 bytes
           need to be added to the returned base address to obtain the
           correct address of the 0,0 pixel.

The above utility obtains the address of the linear frame buffer from the
DGA extension, opens /dev/mem, and plots pixels manually on the linear
frame buffer.

In case you happen to have a FreeBSD box there with a TV tuner, here is a
related utility which uses the same approach to direct a Bt848-based TV
tuner card to display video on the frame buffer:

    http://www.ipass.net/~dbhopper/aa8vb/fxtv/tv-dgatest.c

Randall Hopper
aa8vb@ipass.net

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