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Thread: Direct Color DMA video demos

  1. #31
    I remain nonsequitur Shining Hero sheath's Avatar
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    Barone convinced me to update the console spec sheets on gamepilgrimage with a footnote about this. So I added a footnote to the Genesis and Sega CD spec sheets mentioning "Direct 9-bit RGB (512 colors) available at half horizontal resolution, 160x224 or 128x224 visible, "Chilly Willy," Direct Color Demo using DMA."

    I have two questions for posterity. Is the phraseology correct and concise enough? Also, now that we know how this works is it possible to do something similar on any other platforms with color limitations? Can the SNES display 32,768 colors using the same or a similar method, the TG16 could already display 481 colors technically, but can it do all 512 in direct RGB?
    "... If Sony reduced the price of the Playstation, Sega would have to follow suit in order to stay competitive, but Saturn's high manufacturing cost would then translate into huge losses for the company." p170 Revolutionaries at Sony.

    "We ... put Sega out of the hardware business ..." Peter Dille senior vice president of marketing at Sony Computer Entertainment

  2. #32
    ESWAT Veteran Chilly Willy's Avatar
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    You should give credit to Oerg866 for the original code, and Nemesis for his improvements to the code.

    As for if you can do this with other consoles... on the PCEngine, you could use one of the block transfer commands on the palette registers, but I have no idea how well that would work. I suppose I ought to make a simple demo to see if/how well it works.

    No idea on the SNES... not that familiar with its hardware.

    EDIT: More on the PCE - a quick calculation shows it's not very useful. The block move command takes 17 + 6x cycles, or 6 cycles per byte moved + some overhead. At high speed (7.16 MHz), 6 cycles is 1.19 MB per second; however, it takes two bytes to set the palette entry, or 596.67 KW per second. If the horizontal line rate is 15.7kHz (standard for NTSC), that means you can change the palette entry 38 times per line, which means the resolution would be 32 pixels visible. It's the high-speed DMA in the MD that makes this mode useful, and the PCE doesn't have that high-speed DMA for setting the palette.

    EDIT 2: Looking at the SNES hardware, although the SNES has general purpose high-speed dma, the palette address automatically increments as you DMA (or write with the CPU) the palette data. There doesn't seem to be any way to make it DMA to just the background color register. The MD works because the increment is set specifically for the DMA, so you can DMA to the same palette register continuously.
    Last edited by Chilly Willy; 03-02-2013 at 06:35 PM.

  3. #33
    I remain nonsequitur Shining Hero sheath's Avatar
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    Ah, thanks for the citations for who wrote the original code. Is there a better thread at spritesmind than the one I linked to provide more information? It does seem like you are the one who thought of using Direct Color DMA for actual in game purpose though, is that not the case?

    Unless somebody tells me otherwise I have changed the citation to: Direct 9-bit RGB (512 colors) available at half horizontal resolution, 160x224 or 128x224 visible, "Oerg866," "Nemesis" and "Chilly Willy," "Direct Color Demo using DMA," SpritesMind.net, accessed March 1, 2013, http://gendev.spritesmind.net/forum/...pic.php?t=1203.
    Last edited by sheath; 03-02-2013 at 07:59 PM.
    "... If Sony reduced the price of the Playstation, Sega would have to follow suit in order to stay competitive, but Saturn's high manufacturing cost would then translate into huge losses for the company." p170 Revolutionaries at Sony.

    "We ... put Sega out of the hardware business ..." Peter Dille senior vice president of marketing at Sony Computer Entertainment

  4. #34
    Hero of Algol kool kitty89's Avatar
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    I wonder if that could be used on the Atari ST . . . I think CRAM is updated via DMA in the ST. OTOH, with the ST's DMA bandwidth limited to 4 MB/s and assuming each color entry took 16-bits like in the MD, that would limit it to 1/4 normal resolution rather than 1/2 as in the MD. (or more specifically, you'd get 80 pixels per line . . . or maybe around 96 pixels visible if you're not limited to the same video width restrictions as the normal ST video modes)
    6 days older than SEGA Genesis
    -------------
    Quote Originally Posted by evilevoix View Post
    Dude it’s the bios that marries the 16 bit and the 8 bit that makes it 24 bit. If SNK released their double speed bios revision SNK would have had the world’s first 48 bit machine, IDK how you keep ignoring this.
    Quote Originally Posted by evilevoix View Post
    the PCE, that system has no extra silicone for music, how many resources are used to make music and it has less sprites than the MD on screen at once but a larger sprite area?

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