Changing SRAM on SNES Cart?

[DrMatta]

Hello everyone,

I wasn't sure where to ask this question, I couldn't find the answer I was looking for on this forum, if its been answered before i'm sorry.

What I'm trying to do is create a repro-cartridge of a translated SFC game. This game uses 16 KB SRAM and I have a donor board that is exactly the same, matching LoROM and masks - except it uses 64 KB SRAM.
Does anyone know what tool I can use to change the SRAM check at the beginning of the ROM and/or manipulate the SRAM on the PCB to read 16KB only? I think I read ucon64, but i'm not sure what parameters to give. Also, I'm trying to learn assembly, but am not advanced enough for this specific memory manipulation yet.

Thanks in advance

 

[FAST6191]

Saw your post on RHDN. Repros are generally considered bad news around here as well.

I don't know the SNES specifics for this sort of thing and if it is going to be a simple header tweak, or at least something an automated tool will blow through happily (patching GBA games is a non trivial task if you were going in cold, but we have had tools to do every non anti piracy non hardware quirk game since... quite possibly before street dates when new save types appeared in the wild and if not then measured in days), or whether you will have to go manual. I don't think SNES flash carts (granted I have actively avoided learning too much of the vintage SNES/pre everdrive era flash carts as that way madness lies) nor emulators particularly adopted this approach though.
Going manual would involve finding save routines, figuring out if there is any different handshake/wake up command, figuring out if the protocol is different (some chips might want shorter write commands where others might take several bytes at a time, reading could also be a thing if there is a read verification) and figuring out if there is different "all done here" ending commands. If you are good enough to do that then you could also do save slots, backups (quadruple the size and you could have alternating or more save banks that allow you to fall back to an earlier save in the case of corruption) and more but cross that bridge as and when. SRAM to SRAM is also probably far less likely to incur troubles than if you were going to EEPROM or Flash as those do often switch up protocols and other limitations such that it might need something a bit more radical.
Alternatively SRAM (or possibly FeRAM at this point so as to dodge that battery -- FeRAM was noted as getting popular during the GBA lifetime so would not have been done/been too expensive during the SNES) tends to still be made, and possibly even in pin compatible form or at least something you could do a breakout board or just dead bug for your one off -- if you are already changing ROM chips then 5 more minutes (possibly a bit more more if you have to some cut trace and/or jumper action -- I have not looked at SNES cart PCBs in enough detail but on the N64 and GBA, and in general electronics, plenty of things existed for devs to just drop in a different chip if they cheaped out but did not want to have to do a different PCB design) to swap out to a compatible SRAM replacement is also an option.