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+---- Thread: SRAM Expansion Patch (32Kb) (/thread-3694.html)
SRAM Expansion Patch (32Kb) - madsiur - 05-25-2018
SRAM Expansion
by madsiur
version 1.0
released on 05/25/2018
apply to headerless FF3us 1.0 ROM
wiki entry
download
Description
This hack expand SRAM by $1600 bytes for each save slot, allowing now 8Kb bytes for each save slot plus a third 8Kb for general purpose for a total of 32Kb of SRAM. In original game, only 8Kb of SRAM is used ($306000-$307FFF), each slot occupying $0A00 bytes and $200 bytes for general purpose at the end of the 8Kb block.
With this hack, $306000-$307FFF is used for slot 1, $316000-$317FFF for slot 2 and $326000-$327FFF for slot 3. $336000-$337FFF is used for game SRAM. When you play the game, $7E1600-$7E1FFF is still used and copied to correct slot at saving. $336000-$3375FF is copied to correct slot as extra SRAM. At game loading, correct slot is loaded into $336000-$3375FF and $7E1600-$7E1FFF. So in order to save or load from extra SRAM in your hack, use as an example STA $336000,X or LDA $336000,X.
Since $337600-$337EFF is not used, it means it could be use as scratchpad SRAM for temporary things or have a general use common to the three slots. $337FF0-$337FFF has same function as the original $307FF0-$307FFF.
SRAM could be expanded more but I figured a whole $2000 bytes instead of $0A00 is enough expansion for any hack. In HiROM mapping banks $20-$3F can be used to map SRAM, using always the $6000-$7FFF range of the bank. $C0FFD8 tell the emulator the SRAM size of the ROM.
I have not tested this on sd2snes, everdrive or real hardware. snes9x 1.55 and bsnes+ were used for testing. If you plan to use this hack and make a cart of your hack after, you will need a HiROM cart with a 32Kb memory chip. I have no idea if any existing SNES game has already 32Kb of SRAM.
SRAM map
Code:
Slot 1 expansion: $306A00-$307FFF
$306000-$3069FF = $7E1600-$7E1FFF
Slot 2 expansion: $316A00-$317FFF
$316000-$3169FF = $7E1600-$7E1FFF
Slot 3 expansion: $326A00-$327FFF
$326000-$3269FF = $7E1600-$7E1FFF
Other SRAM values: $336000-$3375FF (game common SRAM)
$337600-$337EFF (unused)
$337F00 = last altered savefile
$337F01 = rng index
$337F08 = fixed value #$E41B (slot 1)
$337F0A = fixed value #$E41B (slot 2)
$337F0C = fixed value #$E41B (slot 3)
$337F0E = fixed value #$E41B (slot 4, useless..)RE: SRAM Expansion Patch (32Kb) - madsiur - 10-04-2018
I commented out one line in the code and updated the patch. I had some minor problems at RAM initialization because because init would be done too late and data would get erased if you had use $336000-$3375FF prior to this.
Code:
//=======================================
// SRAM init
//=======================================
scope lbl_sram_init_sram: {
rep #$20
tdc
tax
init_sram:
sta $306000,x // slot 1
sta $316000,x // slot 2
sta $326000,x // slot 3
// sta $336000,x // you want this line commented likely
// because if you use this RAM for things
// done at game loading, init is done too late
// and data get erased..
inx
inx
cpx #$2000
bne init_sram
sep #$20
rtl
}RE: SRAM Expansion Patch (32Kb) - J92R - 01-03-2019
Pretty sure I could find a good use for this, thank you.
RE: SRAM Expansion Patch (32Kb) - Imzogelmo - 06-03-2019
Offhand, a bestiary comes to mind. Also another project of mine which is in indefinite limbo but could be revived.
One question: I have read somewhere that this space reads/writes slower than the onboard RAM in 7E/7F. Is that true, and would it much matter?
RE: SRAM Expansion Patch (32Kb) - madsiur - 06-03-2019
(06-03-2019, 11:51 AM)Imzogelmo Wrote: I have read somewhere that this space reads/writes slower than the onboard RAM in 7E/7F. Is that true, and would it much matter?
I've never read this but I have not looked for this info either. Where did you read this? I guess it wouldn't change anything if you don't read write often per frame to it, depending of the use some tests would be needed. BTW, FF6-G a japanese hack use the same method, and it is used in various places.
RE: SRAM Expansion Patch (32Kb) - Imzogelmo - 06-05-2019
I'm not sure where I read it but for my purposes the speed probably wouldn't matter so I never looked into it. I was mostly curious if emulators replicated the alleged speed difference.
RE: SRAM Expansion Patch (32Kb) - madsiur - 06-08-2019
(06-05-2019, 08:22 AM)Imzogelmo Wrote: I was mostly curious if emulators replicated the alleged speed difference.
It's the kind of thing I would expect from bsnes and higan. Anything using the snes9x core maybe doesn't.