Sega Saturn "B-Board"

Hi all.

I have an idea for a new project involving fabricating a saturn "B-Board". The board would function out of the cart slot and would interface with a program on the CD drive.

at the moment the card will contain

128 meg of SDRAM operating on a battery backup to make it quasi non-volitile ram so it would act as storage space.

4 meg of normal ram for graphic decompression

The card will also feature a DB25 Connector to upload binary data to the 128meg of ram.

I am in the process of planning the card and at the moment, fabrication costs ar about $380AUS for 2 cards to be made. The card still needs a decent memory controller and maybe additional power source.

My intention for the card is to make it possible to upload STV games to it and play it using a CD that contains LLE information as well as other utilities such as a debugger.

A PC front-end will also need to be written so that it is easy to upload (something like SSFEXE).

I need input from anyone regarding memory addressing issues etc. and some help in writing code to change the saturns control maps.

Also i think that 128meg of ram is too much, maybe 64? depends really on what can be addressed.

If this card ever sees the light of day, then i want to make it possible for people to develop software for it, because it really has many applications.
I assume you're familiar with the restrictions of the cart port? The bus is 16 bits wide and IIRC the address space is only 4MB. Furthermore it seems bus contention could be a serious issue going by the restrictions on use of cartridge RAM in the docs.
ST-V games are mapped in a way diferent of the ordinary Saturn memory map, so ST-V games tru the cart port is a nono. Reverse engennering a card could be interesting, altough. If you're thinking SDRAM for any kind of memory, you also need a nice, somewhat expensive memory controller, and remember it also needs so be in sync with the rest of the diferent-format RAM if you're not looking for crashes every few minutes, i belive. I'm not sure up to what point this could be a probem.
Yeah, bus width is an issue at the moment, as to is the memory controller. I was almost thinking of putting a socket on the card as well for 680x0 processors, but this is jsut overkill. I am still trying to resolve some DMA issues, but hopefully the LLE disk will be able to bypass this.