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Thread: Sega's SVP Chip: The Road not Taken?

  1. #46
    ESWAT Veteran Chilly Willy's Avatar
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    Quote Originally Posted by kool kitty89 View Post
    I don't want to take this too off topic, but Wolf 3D (being a PC game) did all the "3D" scaling (raycasting) effects through software, utilizing the CPU. To take full advantage of the Sega CD (or SNES) it would need to be reprogrammed to take advantage of the hardware scaling capabilities, correct? (though the CD's CPU may have been fast enought alone, and there was a fair amount of RAM)
    If you rewrote the game in assembly, it would be probably very similar to using a 286. Just remember that you didn't run Wolf3D full screen on a 286 and expect it to be playable - that took a 386 or better. Using the CD gate array, you might be able to pull that off. The main problem would be switching to 16 color graphics. Think of it like having EGA rather than VGA graphics. The other issue would be the speed of the CD. A PC would have a pretty fast harddrive to pull data from. The SEGA CD used a 1X CDROM. When you needed to reload data off the drive (which you would with only 512 KB-ish), you'd be waiting full seconds on the CD. We'd consider the old drives the 286 used slow by today's standards, but compared to a 1X CDROM, they were lightning fast.

    But yes, I do think Wolf3D is doable using just the SEGA CD. It would be better with the 32X, but you'd still have an issue with delays due to the slow CDROM. Even the 32X can't make the CDROM any faster.

    Of course, some games (Battle Frenzy, Zero Tolerance, etc) were done on the stock Genesis throgh software (though the limitations showed). It's too bad no games took advantage of the CD's scaling effects like that. (could have made for some pretty good FPS's)


    Anyway, would anyone care to speculate what an adaptor cart using an SH-2 (32X processor) would have cost? (I beleive the stand alone SVP cart was to be arround $50)

    And exactly how expensive would ram expansion be? (if they encorporated something like 1 MB on the cart as well)
    Hard to say. Like I said before, prices are often set by the volume, not the parts. You could make a 32X-ish kind of cart NOW very cheap. Back then? Look at the price of the 32X and then scale it back a little.

  2. #47
    Hero of Algol kool kitty89's Avatar
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    Quote Originally Posted by Chilly Willy View Post
    If you rewrote the game in assembly, it would be probably very similar to using a 286. Just remember that you didn't run Wolf3D full screen on a 286 and expect it to be playable - that took a 386 or better. Using the CD gate array, you might be able to pull that off. The main problem would be switching to 16 color graphics. Think of it like having EGA rather than VGA graphics. The other issue would be the speed of the CD. A PC would have a pretty fast harddrive to pull data from. The SEGA CD used a 1X CDROM. When you needed to reload data off the drive (which you would with only 512 KB-ish), you'd be waiting full seconds on the CD. We'd consider the old drives the 286 used slow by today's standards, but compared to a 1X CDROM, they were lightning fast.

    But yes, I do think Wolf3D is doable using just the SEGA CD. It would be better with the 32X, but you'd still have an issue with delays due to the slow CDROM. Even the 32X can't make the CDROM any faster.
    Would the use of assembly language be for compatability with the 68K architecture, or to take advantage of the scaling hardware?

    Why would a 32X version need to be on CD? Surely a ROM cartridge would be sufficient. (being in the 2-3 MB size)

    Do you think games like Wolf3D could have been done in assembly with the SVP alone without added RAM?

    Also, I know the background would have to be limited 16-colors, but wouldn't sprites have the other 3 16-color palettes available to use?

    Hard to say. Like I said before, prices are often set by the volume, not the parts. You could make a 32X-ish kind of cart NOW very cheap. Back then? Look at the price of the 32X and then scale it back a little.
    Yep, and the lower cost of the SVP chip would have overcome the development costs for such a custom chip with enough volume in sales. But it's a question of how much volume it would take to make it worth using over somthing like an SH-2. (added RAM would be the same price regardless)

    As an in-cart chip (like the FX) it'd be a no brainer that the SVP would be cheaper (assuming you released more than one game using it, with the single release a lock-on cart would obviously be pointless). However, in a lock-on set up the circumstances are a bit different (the volume would be independent of the number of games produced using it) and the added RAM becomes feasible. (wich would be prohibitably expensive on an in-game cart if used in any significant amount)

  3. #48
    ESWAT Veteran Chilly Willy's Avatar
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    Quote Originally Posted by kool kitty89 View Post
    Would the use of assembly language be for compatability with the 68K architecture, or to take advantage of the scaling hardware?
    Neither. It would be to maximize speed while minimizing the space required by the code.


    Why would a 32X version need to be on CD? Surely a ROM cartridge would be sufficient. (being in the 2-3 MB size)
    Since I released the cart version, people have been bugging me for a CD version as well. There are a few reasons. First, you wouldn't need a flash cart to play it on real hardware. Second, you could support the commercial versions with the same executable. I obviously can't release versions of Wolf32X using the full files, just the shareware ones.

    Do you think games like Wolf3D could have been done in assembly with the SVP alone without added RAM?
    With the extra ram the SVP had, probably. With just the 64 KB in the Genesis itself? You'd have to chop it up too much. For example, just tracking the "objects" used by Wolf3D (items, enemies, etc) requires a lot of ram. You could do a raycasting type game, but it wouldn't really be Wolf3D. So if you meant a game in the same genre, yes, the SVP would handle that just fine. With some judicious use of assembly, it could probably even handle Doom-genre games. But Wolf3D or Doom themselves? You could make something that imitated it, but wasn't really Wolf3D or Doom. It depends on how picky you are about what you call Wolf3D or Doom.

    Also, I know the background would have to be limited 16-colors, but wouldn't sprites have the other 3 16-color palettes available to use?
    Yes, that's one of the things that could be done to help with the graphics. Use the palettes for objects separately from the background.


    Yep, and the lower cost of the SVP chip would have overcome the development costs for such a custom chip with enough volume in sales. But it's a question of how much volume it would take to make it worth using over somthing like an SH-2. (added RAM would be the same price regardless)

    As an in-cart chip (like the FX) it'd be a no brainer that the SVP would be cheaper (assuming you released more than one game using it, with the single release a lock-on cart would obviously be pointless). However, in a lock-on set up the circumstances are a bit different (the volume would be independent of the number of games produced using it) and the added RAM becomes feasible. (wich would be prohibitably expensive on an in-game cart if used in any significant amount)
    What I'd love to see is a new cart that had a FPGA and some ram on it. You could actually program the FPGA to act as the SVP. That would allow the creation of SVP games other than Virtua Racing.

  4. #49
    Mastering your Systems Shining Hero TmEE's Avatar
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    The FPGA cart would be fun thing to mess with, and with that you have freedom to enhance stuff, perhaps a nice patterntable and tile generator that gives you nicely worked out 31 color data with minimal VDP bandwith requirement :P
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    Hero of Algol kool kitty89's Avatar
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    Quote Originally Posted by Chilly Willy View Post
    With the extra ram the SVP had, probably. With just the 64 KB in the Genesis itself? You'd have to chop it up too much. For example, just tracking the "objects" used by Wolf3D (items, enemies, etc) requires a lot of ram. You could do a raycasting type game, but it wouldn't really be Wolf3D. So if you meant a game in the same genre, yes, the SVP would handle that just fine. With some judicious use of assembly, it could probably even handle Doom-genre games. But Wolf3D or Doom themselves? You could make something that imitated it, but wasn't really Wolf3D or Doom. It depends on how picky you are about what you call Wolf3D or Doom.
    When I said without added RAM, I meant excluding the added 1-2 MB on cart possibility. However, I'd though the only added memory was the 2 kB or I-RAM (that's all Ken Horowitz's article mentioned, and for some reason listed it twice in the Super FX comparison table: under both RAM, and Memory -Cache-).
    Reading through that doccument on the SVP you linked to earlier though, I now see that the Virtua Racing cart also carried 128 kB of DRAM. (incedentally the same amount carried in Super FX carts, -1 Mb according to Horowitz's article, albeit with only 1/4 the Cache RAM available)

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    Excellent article, Excellent thread!

    The svp chip could've been sold separetly in a Sonic & Knuckles type of cartridge, and with games like Virtua Fighter, Star Wars Arcade, and Daytona USA released for it as MR. Horowitz mentioned in the article they would've indeed spared some troubles caused by releasing the 32x add on.
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    Shining Hero Joe Redifer's Avatar
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    The table chart shows that the SVP had PWM channels? This be true? It surely wasn't used for Virtua Racing.

    EDIT: Went back and read Tiido's posts. No extra sound. I wonder who came up with that? Did anything except the 32X itself take advantage of those two audio cart pin slots?
    Last edited by Joe Redifer; 01-01-2011 at 04:44 PM.

  8. #53
    ESWAT Veteran Chilly Willy's Avatar
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    Quote Originally Posted by Joe Redifer View Post
    The table chart shows that the SVP had PWM channels? This be true? It surely wasn't used for Virtua Racing.

    EDIT: Went back and read Tiido's posts. No extra sound. I wonder who came up with that? Did anything except the 32X itself take advantage of those two audio cart pin slots?
    The VR cart indeed does not even connect to the audio lines on the cart port, so there is no possibility it does audio... at least in that sense. However, it IS a DSP with 128KB of DRAM... you could easily use it for wavetable synthesized music and digital sfx, all added together and fed to the PCM channel in the YM2612.

    The only other thing I know of that uses the audio in lines on the cart port is the FM chip for SMS mode on the Neo Myth 3-in-1 MD flash cart. Note that the Nomad doesn't support those lines, so you don't get FM with the Myth on the Nomad. Maybe Tiido can come up with a hack for that.

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