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Thread: Possible details of the Saturn’s “3D upgrade cartridge”

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    Saturn Possible details of the Saturn’s “3D upgrade cartridge”

    Many will have read the rumours of an upgrade for the Saturn that would have given the console improved 3D graphics. Although the magazines of the day suggested the upgrade would feature a Real3D graphics chip (as that was what the Model 3 was using in the arcade), I’m not sure if there was anything to that rumour.

    However, today I came across a very interesting patent from Sega, filed in February 1997. It describes an “Enhanced function board for use in processing image data and image processing using the same” and can be found here: https://patents.google.com/patent/US5946004A/en

    The patent describes an add-on to the Saturn's architecture that features two floating point DSPs, another VDP1(!) with its own VRAM and Frame Buffer RAM, plus 512K (4Mbit) of Texture Memory.

    The output from this additional VDP1 is fed into the VDP using the EXBG interface. On looking at the schematics, it appears that EXBG is surfaced to the MPEG port on the SH1 daughterboard (as expected), but also to the cartridge slot, suggesting that such a solution could have been implemented as a Saturn cartridge.

    Looking at the detail of the patent, the function board connects to both the A-Bus (where the CD-ROM and cartridge slots are located) and the B-Bus (where the VDP1, VDP2 and SCSP sit). It doesn’t look like the cartridge slot has a connection to the B-Bus, so the function board as described isn’t directly compatible with the Saturn. The diagram in the patent also shows an illustration with a Jamma connector, so perhaps it was originally meant for an STV type unit.

    Since both Model 1 and 2 made use of DSPs for doing the heavy maths, it’s perhaps not surprising that Sega followed a similar approach with this function board, but the addition of another three processors to the Saturn’s existing eight processors is a bit mind boggling!

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    Raging in the Streets Blades's Avatar
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    "No challenge facing humanity can't be solved with more processors" - Sega, 1991-1998.

    Jokes aside, that's a great find. Indeed looks like it might be more for the ST-V.

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    Hero of Algol TrekkiesUnite118's Avatar
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    This could also just be a patent for the MPEG card. It's vague enough that it could technically work for that as that card has additional chips on it to decode MPEG-1 video, JPEG images, and MP2 audio as well as having memory to use as decoding buffers that can be piped to either EXBG or DMA'd over to RAM.

    It could also just be a patent for explaining that functionality which is built into both the Cart slot and the MPEG slot on the Saturn.

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    Master of Shinobi
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    Yeah, I agree, that looks like an STV upgrade. They even mention the base motherboard having 4 connectors through which the Enhanced Function Board connects, which is exactly how the STV is set up, just look at one.

    After reading it, it feels that it is more like hooking up another Saturn into a Saturn. Just substitute DSP0/1 with SH2 Master/Slave. Those too had a separate Work memory (the SDRAM, first megabyte of memory) and Texture memory (the 16-bit DRAM, second megabyte of memory), and if I recall right the internal 4k cache could be used as a FIFO to communicate between the two chips. All of those match the patent.
    However the patent does mention that the DSPs are on independent buses, so then maybe not the SH2s. Maybe they learned that lesson.

    This theoretically doubles the polygon power of the machine, but you'd still have to deal with all the idiosyncrasies of the VDP1, plus now you have to deal with the overlap problems of the second VDP1 effectively being a VDP2 background. Meaning you cannot freely mix the two VDP1s graphics, you'd have to use one as a backplane and another as the front. Or you use paletted graphics where you can have per polygon sorting with up to 3 bits precision (wow), but now you can't do polygon transparency and lightning becomes a bitch to do. The up side is that they only really need to do one new custom IC, that would translate the VDP1EX framebuffer into an output that the VDP2 EXBG expects (including separate color RAM!), plus have the two DSP chips which could be repurposed Model 2 chips for all we know. They just have to crunch matrix transformations really fast.

    It's like if the Saturn got its own 32x with a VDP1 inside. Definitely more advantageous for the Arcade scene where the cost is less of an issue. The patent even mentions the cart bus and has a diagram for how to stack the PCBs for this purpose.

    It should also be noted that Sega did something conceptually similar with the Naomi 2 arcade board which included an extra t&l chip and a second PowerVR2 GPU. It seems they explored this area much earlier.

    Quote Originally Posted by TrekkiesUnite118 View Post
    This could also just be a patent for the MPEG card. It's vague enough that it could technically work for that as that card has additional chips on it to decode MPEG-1 video, JPEG images, and MP2 audio as well as having memory to use as decoding buffers that can be piped to either EXBG or DMA'd over to RAM.

    It could also just be a patent for explaining that functionality which is built into both the Cart slot and the MPEG slot on the Saturn.
    Definitely not the MPEG card. The first part of the patent describes the Saturn/STV, but the stuff for the "enhanced function board" specifically states doing 3d workloads, such as affine transformation of textures and perspective processing to get the Z order, which are then fed into a VDP1EX, which is fed into an IC that has its own Color RAM to convert the framebuffer into an RGB output, which is then fed into the EXBG of the VDP2.
    Fig.3 on the patent is also very specific to the STV, such as the 4 connectors on the mainboard, onto which you plug the Enhanced Function Board, onto which you can put a Communications board (not sure if they ever made one for the STV?), onto which you can put a CD-ROM board and sub-board (this one was used for that one fishing game for STV, it's basically the SH1 board from VA0 Saturns, plus a SCSI CDROM).

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