jlange@emx.utexas.edu (John Lange) (11/11/90)
I am working on an application which must be completed very quickly. Any help with the problem described will be greatly appreciated. I am trying to use the super VGA modes for scrolling. Specifically, I am using the Orchid Prodesigner II based on the Tseng ET4000 chip, although the problem is generally applicable to other types of super VGA. The board has 1 MB of memory. Briefly, there are 2 ways to scroll, I think. One is to bitblt the previous image into the desired new location. This is easy and works for just about everything. This method is inappropriate because it is too slow for my application. The other way to scroll is to adjust the start address of the screen refresh. This works well in some video modes. For example, 640x480x16 works fine. 1024x768x16 works fine. These work partially because they are implemented with bit plane memory. That is, each bit plane has a block of memory on the video card. I really need to get 1024x768x256 to scroll, with the start address selectable to any place within the 1 MB of video memory. Unfortunately, there are (seem to be) 18 bits of address space available to select the start address when 20 are really needed. This mode is different than the other two in terms of how memory is organized. With 1024x768x256, each byte represents a pixel (the bits in the byte represent the color planes). Am I trying to do something that is impossible? Does anyone know of other methods of scrolling in 1024x768x256? I might also choose the 34010 with or without TIGA route. However, in the reference manual for the 34010, it seems that only 16 bits are available for setting the start address. I don't have any experience with programming the 34010, so the learning curve might also be a factor. Is it possible to set the start address anywhere in video memory with the 34010 based boards? Does anyone know of inexpensive 34010 based boards? Thanks in advance for your help. John Lange jlange@emx.utexas.edu or johnl@walt.cc.utexas.edu 512-454-4797 (work) 512-835-2790 (home)
jlange@ut-emx.uucp (John Lange) (11/12/90)
If anyone is interested, I figured out how to make 1024x768x256 scroll using the Tseng ET4000 chip. In article <39505@ut-emx.uucp>, jlange@emx.utexas.edu (John Lange) writes: > to any place within the 1 MB of video memory. Unfortunately, there are > (seem to be) 18 bits of address space available to select the start > address when 20 are really needed. This mode is different than the > other two in terms of how memory is organized. With 1024x768x256, each > byte represents a pixel (the bits in the byte represent the color planes). The trick is that incrementing the start address by 1 increments the actual start address by 4! Thus, 18 bits are all that are needed to address all 1 MB of video memory. I'm still interested in anyone's comments about how to do the same thing with the 34010. I plan on calling TI tomorrow to try to find out, but chances are we will use the Tseng chip since it is so much cheaper and does what we want.