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Topic: Adding SRAM to a NES ROM... (Read 2 times)
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Vanya
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« on: October 31, 2008, 01:51:21 am » |
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... what would it take and what would I need to know to do it?
Would I have to be using a certain mapper to be able to use saves?
I'm asking for my MM5 hack. There are may asking for this feature and I'd like to deliver. =)
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KingMike
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« Reply #1 on: October 31, 2008, 08:15:37 am » |
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You can add it to most mappers.
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Gideon Zhi
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« Reply #2 on: October 31, 2008, 08:47:30 am » |
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Recoding the game to do something WITH the sram is another story. Enabling it, I think, is generally pretty simple.
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Disch
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« Reply #3 on: October 31, 2008, 10:09:11 am » |
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MM5 already uses mapper 4 - which can use SRAM just fine, assuming you turn it on.
Read: Basic asm knowledge required
1) Turn on the "battery backed" bit in the header (bit 1 of offset 0x00006). This is what tells the emulator to create the .sav file for this game.
2) Assuming MM5 doesn't already do it, Enable PRG-RAM by writing $80 to $A001 sometime at game startup -- like in the Reset code (read: not offset 0xA001 -- I'm talking about an in-code asm change)
3) Write the data you want saved anywhere to RAM at $6000-7FFF that isn't already being used by the game
4) When loading a game, simply read the data from $6000-7FFF just as you would normally
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KingMike
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« Reply #4 on: October 31, 2008, 03:00:47 pm » |
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Of course, the tricky thing would be figuring out where the data from the passwords goes into RAM.
(luckily I think all the Mega Man password schemes have been cracked. So that's a bit less work, but you'd probably still need to work out the binary representation.)
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Vanya
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« Reply #5 on: November 01, 2008, 04:09:58 pm » |
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That sounds a lot easier than I thought it would be. Thanks a lot for the info, guys! ^_^
Having multiple files would just be a matter of coding the game to read/write to certain areas in $6000 - 7FFF, right?
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Disch
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« Reply #6 on: November 01, 2008, 04:47:28 pm » |
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yup.
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Vanya
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« Reply #7 on: November 01, 2008, 07:45:13 pm » |
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Excellent!  |
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