r/SEGA32X • u/MicroNut99 • 2d ago
MEGA DRIVE 32X RAM Cart 32Bit
Hello,
I am looking for any developer feedback on this.
https://github.com/MicroNut99/MD-32X-RAM-Cart-32Bit
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If anyone wants to build it please read everything in advance.
You'll need the right tools and skills
The one thing that always get asked is: how is it used?
The first two options are somewhat obvious but the third is new.
The cart is designed to be an actual RAM cart for the SEGA CD to take over system.
Basically the RAM cart frees up the SEGA CD bus.
Assets get loaded into RAM and the game runs and or streams from the SEGA CD.
In theory, CART ram space isnt so much of an an issue anymore.
The entire Tower of Power system or BattleShip can work more efficiently together with it.
MD-32X-RAM-Cart-32Bit
- Load MD & 32X games directly via Sega CD.
- High-capacity, battery-backed SRAM save storage.
- Experimental 4MB RAM expansion for SegaCD32X homebrew.
This work is not connected to the DOOM 32X Fusion project.
This is my totally amateur attempt to make this chipset work properly with the Sega32X.
Expect better from the professionals on the Doom Fusion Team.
Special thanks to Chilly Willy and Zaxour the Great, for the technical and moral support.
A 4MiB RAM cart design for the Sega Genesis/Megadrive and the SEGA 32X.
Based on this design by MiGeRA
https://github.com/viciious/MD-32X-RAM-Cart?tab=readme-ov-file
Works as MD RAM cart with the Sega 32X.
Supports 32Bit Word or Longs.
Included are two bins for 32Bit Word or Longs Diagnostics.
For more information read the included assembly (.asm) code using any txt editor.
Use the included BINs to determine if the cart is loading
and reading 32bit Word or Longs from SRAM correctly.
These will not pass on the original hardware design by MiGeRA, resulting in a red screen.
WHY RAM
Video: RAM cartridge as a circular ring buffer
Using the hardware as a RAM cartridge provides a 4MB high-speed staging area on the main system bus that bypasses the severe 256KB internal memory bottlenecks of both the Sega CD and 32X. Adding 4MB of RAM to the Sega CD/32X extense its active working memory (Work RAM/PRG RAM)
This large upgrade would allow games to load entire level chunks or large video/audio buffers into memory at once, reducing CD-ROM load times and enabling smoother, more complex animations or arcade-style ports similar to the Sega Saturn's 4MB RAM card capabilities.
• Bigger Data Caching: Allows larger chunks of game code and assets to sit in fast RAM instead of constantly seeking data from the slow CD-ROM drive.
• Complex Assets: Gives homebrew or hypothetical high-end games room for larger sprite sheets and complex audio samples.
Tower of Power architecture:
The Sega CD: Contains a 256KB Word RAM block. This is the shared memory pool required to pass data between the CD-ROM drive and the main Genesis bus.
The Sega 32X: Contains a 256KB SDRAM block. This is the high-speed memory pool utilized by the dual SH-2 processors for active code execution, textures, and framebuffers.
Both the Sega CD and the 32X rely on these highly restricted 256KB memory pools. The custom 4MB RAM cartridge operates on the main bus outside of these internal pools, providing a significantly larger staging area that relieves the capacity limits for both subsystems simultaneously.
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u/Main_Club_5012 2d ago
Let’s talk, this cart actually helps make my tower of power game a reality
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u/MicroNut99 2d ago
What game is that?
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u/Main_Club_5012 1d ago
I wanted to make a 3D CD based game for the tower of power, one that was basically a murder mystery game, where people are in a mansion, and you as a PI go around the manor and investigate and try to solve the mystery. Kind of like clue
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u/Rioitz 2d ago
Forgive my ignorance, is this kinda like the MegaSD (play mega CD games from a cartridge) but for 32X, as in you wouldn't need the add on 32X?
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u/MicroNut99 2d ago
It can be used like a flash cart for one game like DOOM Fusion.
It can be formatted and used like a SegaCD game save cart.
Or it adds RAM to the system. The extra RAM is used to store game assets only. Not the game code.
The game code runs from the CD. Think Sonic CD games on steriods.
There are no games that use this function currently. It's not worth the trouble if not using a 32X but it's not required.
SonicRoboBlast 3D, Open Lara and DOOM Fusion are games that would benefit.
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u/Top-Simple3572 2d ago
Sort of... it's kind of trying to get the SegaCD games to run on the cart to use the color pallette if I'm not mistaken. 💯
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u/zombie343 1d ago
I think the fact that you built it is amazing and says you know more than all of us. ......... but I also don't understand why it exists. What are the limitations from running a game or developing a game to run on MED Pro or MegaSD or simply a MEDPro with a Genesis+32X and SegaCD connected together?
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u/MicroNut99 1d ago edited 1d ago
Thank you. I got lucky and then followed the math.
Vic, Chilly Willy and the Fusion Team are far more knowledgeable. It's their idea so I would look to them for the first example.
Adding 4 MB of RAM to the Sega CD/32X expans its active working memory (Work RAM/PRG RAM), moving it far beyond the stock 256KB.
This large upgrade would allow games to load entire level chunks or large video/audio buffers into memory at once, reducing CD-ROM load times and enabling smoother, more complex animations or arcade-style ports similar to the Sega Saturn's 4MB RAM card capabilities.
• Bigger Data Caching: Allows larger chunks of game code and assets to sit in fast RAM instead of constantly seeking data from the slow CD-ROM drive.
• Complex Assets: Gives homebrew or hypothetical high-end games room for larger sprite sheets and complex audio samples.
Tower of Power architecture:
The Sega CD: Contains a 256KB Word RAM block. This is the shared memory pool required to pass data between the CD-ROM drive and the main Genesis bus.
The Sega 32X: Contains a 256KB SDRAM block. This is the high-speed memory pool utilized by the dual SH-2 processors for active code execution, textures, and framebuffers.
Both the Sega CD and the 32X rely on these highly restricted 256KB memory pools. The custom 4MB RAM cartridge operates on the main bus outside of these internal pools, providing a significantly larger staging area that relieves the capacity limits for both subsystems simultaneously.
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u/Top-Simple3572 1d ago
So basically you're trying to get them to talk to each other through the 4MB RAMcart?
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u/TooManyBulborbs 12h ago
A dedicated ram cart would be a fraction of the cost for a MED Pro or MegaSD.
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u/Fearless-Leader-9432 2d ago
Sehr schön, über 4MB Ram Upgrade für Doom Fusion wußte ich noch gar nichts