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Compute checksum for extended SRAM

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Validate SRAM on file screen load and delete if checksum incorrect
This commit is contained in:
cassidoxa
2022-07-25 22:19:06 -04:00
parent 0e6e5d5b45
commit 10079a539b
3 changed files with 56 additions and 18 deletions
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50
save.asm
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@@ -1,12 +1,40 @@
;--------------------------------------------------------------------------------
Validate_SRAM:
REP #$30 ; vanilla behavior from $0CCD45, includes prize pack reset after save and quit
LDX #$00FE : -
STZ $0D00, X
STZ $0E00, X
STZ $0F00, X
DEX #2
BPL -
WriteSaveChecksum:
LDX.w #$0000 : TXA : - ; Checksum first $04FE bytes
CLC : ADC.l SaveDataWRAM, X
INX #2
CPX #$04FE : BNE -
LDX.w #$0000 : - ; Checksum extended save data
CLC : ADC.l ExtendedFileNameWRAM, X
INX #2
CPX #$0FFE : BNE -
STA.b $00
LDA.w #$5A5A
SEC : SBC.b $00
STA.l $7004FE
RTL
;--------------------------------------------------------------------------------
ValidateSRAM:
REP #$30
LDX.w #$0000 : TXA : - ; Checksum first $04FE bytes
CLC : ADC.l CartridgeSRAM,X
INX #2
CPX.w #$04FE : BNE -
LDX.w #$0000 : - ; Checksum extended save data
CLC : ADC.l ExtendedFileNameSRAM, X
INX #2
CPX #$0FFE : BNE -
STA.b $00
LDA.w #$5A5A
SEC : SBC.b $00
CMP.l InverseChecksumSRAM : BEQ +
TDC : STA.l FileValiditySRAM : + ; Delete save by way of zeroing validity marker
LDX.w #$00FE : - ; includes prize pack reset after save and quit
STZ $0D00, X
STZ $0E00, X
STZ $0F00, X
DEX #2
BPL -
SEP #$30
RTL
;--------------------------------------------------------------------------------
@@ -23,6 +51,11 @@ ClearExtendedSaveFile:
STA $700D00, X
STA $700E00, X
STA $700F00, X
STA $701000, X
STA $701100, X
STA $701200, X
STA $701300, X
STA $701400, X
RTL
;--------------------------------------------------------------------------------
ClearExtendedWRAMSaveFile:
@@ -125,5 +158,4 @@ CopyExtendedWRAMSaveFileToSRAM:
REP #$30
PLB
PLA
LDX.w #$0000 : TXA ; what we wrote over
RTL