SNES CD-ROM question

Discussion of hardware and software development for Super NES and Super Famicom.

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byuu
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Re: SNES CD-ROM question

Post by byuu » Sat Sep 08, 2018 7:53 pm

But full-screen (256x224, 8-bit, @ 30fps) doesn't seem like a possibility without additional hardware.
I mean 256x224x8bpp@30fps is just plainly impossible no matter how much hardware you throw at it. The only way you'll get that is with a 32X style link where the SNES video out goes into the add-on unit, and the add-on unit outputs its own video signal that super imposes one device onto the other.
You got that wrong. MSU-1 is just a storage device (like CDROM).
The only thing that prevented something like the MSU1 existing in 1998 was that the cartridges would be the size and cost of Neo-Geo games. I don't think "marginally better audio quality and four minutes of cutscenes" would justify someone to pay $400 instead of $60 (in 1998 money) for a game ^^;
Also SNES could do a DMA from some open-bus address to PPU, there's nothing preventing the base unit from outputting data upon PPU writes (as long as there's an I/O port for disabling that behaviour, so the CPU could also write to PPU without getting disturbed by the base unit).
I mean, tricks like that are truly starting to abuse the hardware. But yeah, the 21fx actually hijacks $fffc,fffd vector reads and redirects it from the expansion port alone, so yes, it's technically possible. But it's really, really, really not supposed to be.

calima
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Re: SNES CD-ROM question

Post by calima » Sun Sep 09, 2018 1:18 am

Given how little cpu Cinepak takes, it's conceivable an existing chip like SA-1 could decode that.

Oziphantom
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Re: SNES CD-ROM question

Post by Oziphantom » Tue Sep 11, 2018 6:49 am

Just found this https://m.youtube.com/watch?v=oOowlcsADt4 FMV on a VIC-20. Its monochrome only though..

We were able to get this working on a C64 https://www.youtube.com/watch?v=2yG36ROGdYA its only 1/4 size and 15fps but its FMV ;)

If you give a C64 a DMA engine then https://youtu.be/wNT3E1KGboU?t=105

Give this already exists https://youtu.be/Gm9lgIzjlK8?t=99 without the CD add on.

I would think given limits you could get movie playback. I mean you could even interlace the frames and use HDMA to pull the fields out such that each alternative line was in sequence in VRAM so you can DMA frame updates to a half per frame. You would keep the screen map static so you just have to update 32x14 = 448 tiles, at 16 colour mode is still 14K if my maths is right... which would take about 2 frames to transfer so you could do a field at 30fps, so a frame at 15fps. If you narrow the "fmv" then you might be able to get more, of if you make the alternative frame Scan Lines like C&C did then you can double the frame rate. Something like the 90s Anime style would probably delta compress really well as you would only need to handle the tiles that change in a frame which given the large areas of solid colour, is probably not that much for most frames.

tepples
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Re: SNES CD-ROM question

Post by tepples » Tue Sep 11, 2018 8:22 am

calima wrote:Given how little cpu Cinepak takes, it's conceivable an existing chip like SA-1 could decode that.
The 2x2 pixel and 4x4 pixel blocks of Cinepak are more convenient to write out in a packed pixel format (like Sega Genesis) than a planar one (like Master System/Game Gear, Game Boy, and Super NES/TG16). How easily would SA1 cover the difference?

Revenant
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Re: SNES CD-ROM question

Post by Revenant » Tue Sep 11, 2018 8:31 am

What if you used mode 7 to get packed pixels and then used the background scaling to handle the screen resolution / codebooks? You could, for example, scale the background down to use individual tiles as codebook entries, or something like that.

Oziphantom
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Re: SNES CD-ROM question

Post by Oziphantom » Tue Sep 11, 2018 8:45 am

tepples wrote:
calima wrote:Given how little cpu Cinepak takes, it's conceivable an existing chip like SA-1 could decode that.
The 2x2 pixel and 4x4 pixel blocks of Cinepak are more convenient to write out in a packed pixel format (like Sega Genesis) than a planar one (like Master System/Game Gear, Game Boy, and Super NES/TG16). How easily would SA1 cover the difference?
The SA-1 has a bitmap -> tiles conversion for "free" in its DMA controller. So you get the SA-1 to convert the Bitmap into tiles to WRAM then get the SNES DMA to pump it to VRAM.

calima
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Re: SNES CD-ROM question

Post by calima » Tue Sep 11, 2018 10:38 am

On the c64/anime front, we already have the Pokemon anime intro for GBC, packed as tiles. The compressor is open source.

lidnariq
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Re: SNES CD-ROM question

Post by lidnariq » Tue Sep 11, 2018 11:05 am

Oziphantom wrote:Just found this https://m.youtube.com/watch?v=oOowlcsADt4 FMV on a VIC-20. Its monochrome only though..
Given how the VIC-20's video mode works, I'm certain they could trivially change it to 96x160 4-color mode... they clearly already support changing the background color.

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Punch
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Re: SNES CD-ROM question

Post by Punch » Tue Sep 11, 2018 12:30 pm

Life finds a way. :lol:

https://www.youtube.com/watch?v=19XdGJh6Znc

I'm sure the SNES with a PCE CDROM style attachment could do better.
This is a block of text that can be added to posts you make. There is a 255 character limit.

Oziphantom
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Re: SNES CD-ROM question

Post by Oziphantom » Wed Sep 12, 2018 4:49 am

Isn't the Super CD suppose to have the GSU2? That is able to make bitmap data and have the SNES throw it on screen?

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LuigiBlood
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Re: SNES CD-ROM question

Post by LuigiBlood » Wed Sep 12, 2018 5:14 am

I just want to correct a few things about SNES CD:
There are two of them, there's the Super Disc from Sony, the prototype that we ended up getting, which is just basically a regular double speed CD-ROM drive plugged to the EXT port alongside a BIOS cartridge.

Then there's the Philips one that adds the additional processing unit to it (estimated to be a NEC V810, same CPU as Virtual Boy because of cache size), and also, one detail that has been omitted to be mentioned here and I feel it's important: The drive is connected to the cartridge with a cable. That's in the specs, you can find it. Potentially could use both A-bus and B-bus.

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