Author Topic: Mega Everdrive hardware for homebrew dev (SDRAM access)  (Read 3919 times)

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Offline Zontar

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Mega Everdrive hardware for homebrew dev (SDRAM access)
« on: October 11, 2013, 06:27 AM »
I am currently in the planning stages of a two-dimensional Minecraft-type creative game. Minecraft-type games typically require a lot of RAM, so I've been exploring ways around the 64KB conventionally available to programs. One of my ideas was to use a custom cart with SDRAM inside; that is, until I realized that's basically what the Mega Everdrive is! So I have a few questions to investigate the feasibility of this:

1. From what I understand, the game is copied into SDRAM when selected. Is the SDRAM writable after a game is loaded? I ask because some games may write to ROM to check for cartridge copiers, and I'm unsure if there were any countermeasures you took by default to make these games compatible with the unit (and whether or not those countermeasures can be "turned off" by a program)

2. Is there any bank-switching method (mapper, etc) coded into the FPGA to permit addressing beyond the standard 4MB of ROM to megadrive titles? Is the SSF2 mapper available and can it be used for this purpose?

Thank you very much.

Offline KRIKzz

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Re: Mega Everdrive hardware for homebrew dev (SDRAM access)
« Reply #1 on: October 11, 2013, 01:48 PM »
By default write acces is closed, but mega-ed has exteded SSF2 mapper for homebrew. With SSF2 mapper you can take acces to whole 16, or may be even 32Mbyte of sdram (all late carts has 32Mbyte), also you can write to sdram just like in nortal ram. You can read about extended SSF2 mapper here: http://krikzz.com/pub/support/mega-ed/dev/extended_ssf.txt

Offline llioncourt

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Re: Mega Everdrive hardware for homebrew dev (SDRAM access)
« Reply #2 on: October 13, 2013, 01:49 AM »
How to know if my cart has 16 or 32mb of SDRAM?

Offline KRIKzz

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Re: Mega Everdrive hardware for homebrew dev (SDRAM access)
« Reply #3 on: October 13, 2013, 05:57 PM »
Next OS release will show information about SDRAM size in menu, but right now you can open the cart and look at the sdram chip. 48LC8M16 means 16Mbyte, 48LC16M16 means 32Mbyte. At this moment more easy to find 32Mbyte chips, so, i decide to use 32M, but extra 16M is not used, probably extra memory useful only for homebrew developers only