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When's the SD Multicart Coming Out?


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It can be done. The question is how much work and who will spend the time to do it. :)


Two different ways it could technically be possible. I'm not sure if the first is even a "thing". Keep in mind these are my wild guesses, and may or may not be possible. I'm also being very generic about this, and not even bringing up GROM and it's idiosyncrasies :)


1) SD is a serial technology. The TI Bus is a parallel data bus (data lines, address lines). Potential to map serial to parallel with some kind of chip. Probably not a good idea, because you can only load one program on the SD at a time, which defeats a multicart (but then again, if you bank switch it, you can go up to A3, and theoretically use 32MB of the SD.) Still a pretty good waste of space, even if we can find a discrete chip to bank up to 32MB (the 377 banks up to 2M, for example).


2) Replace the EEPROM with a parallel RAM chip. Have a microcontroller load the info from the SD onto the RAM chip (i.e. if contents in RAM and not empty, load a boot program; if empty, load a default menu type program into the RAM chip). Banking would have to be figured out or redesigned, due to you actually banking by writing to RAM, and then again, you'd be limited by the 377 to 2M, when we COULD possibly go to 32M.


2a) Another way you could do step #2 is have a microcontroller, RAM, and EEPROM. Essentially, start with a blank slate at >6000 RAM. Power up. If empty, copy menu to >6000 and run. Menu can either load images, or look on the EEPROM and you can just hit a key to load what was previously loaded into the EEPROM (it could essentially copy it to the RAM chip from the EEPROM and just run it. That way, you have something that survives a power off.) If you instead choose a new program, it'll load it into the EEPROM, then copy it to the RAM chip and then run it.


The UberGROM board does have enough I/Os on it to potentially interface with a SD card. Can it potentially do everything we want as far as making a SD Multicart? Well, it can't yet flash the EEPROM 49F040 yet without additional hardware (or if some entrepreneur programmer wants to figure it out). People have figured out how to at least interface a SD card with an Atmega; look at all the Arduino shields, and even projects like this. http://www.engineersgarage.com/embedded/avr-microcontroller-projects/sd-card-interfacing-project



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