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Any gotchas with save game RAM?
slobu - Aug 31, 2011
  slobu Aug 31, 2011
I'm thinking an RPG Maker concept would be possible if I can count on the typical 8k save game RAM. Any gotchas people have found out about? It's battery backed RAM so it wouldn't have the limited read/write cycles of flash. Don't see why an end-user constantly saving and reading all 8k constantly would be an issue.

 ExCyber Aug 31, 2011
Are you talking about designing your own cartridge, or using an existing one (or emulators/copiers)?

 slobu Aug 31, 2011

ExCyber said:
Are you talking about designing your own cartridge, or using an existing one (or emulators/copiers)?


Well, the only service I know is gamereproductions.com and they scavenge existing commercial boards. So I would probably be working around the fact they had only one memory tied to the low byte of the bus. What do people usually call it? 8-bit SRAM?

I guess I could try and make a run out of just Tototek 32meg carts but that could get pricey and who knows about how many are left..

 Chilly Willy Sep 1, 2011
If you use the Tototek carts, you have four banks of 32KB of sram accessed on odd bytes from 0x200001 to 0x20FFFF. If your game is 2MB or smaller, enable the sram in the cart init code and just read/write the sram without worry. If you cart is over 2MB, then you need to disable ints, enable the sram, read/write the byte(s), disable the sram, and finally enable ints.

Remember that words and longs maybe be read/written to sram using the movep.w movep.l opcodes on the 68000. Bytes just use the regular move.b instructions.

enable sram (write-enabled)

Code: 
  
        move.b  #1,0xA130F1         /* SRAM enabled, write enabled */

disable sram

Code: 
  
        move.b  #0,0xA130F1         /* SRAM disabled */