Merge pull request #42 from zohassadar/mmc3

MMC3 Init Adjustment

Author: kirjavascript

src/io.asm

@@ -49,6 +49,7 @@ MMC1_CHR1   := $DFFF
 MMC3_BANK_SELECT := $8000
 MMC3_BANK_DATA := $8001
 MMC3_MIRRORING := $A000
+MMC3_PRG_RAM := $A001
 
 .macro RESET_MMC1
 .if INES_MAPPER = 1

src/reset.asm

@@ -1,18 +1,5 @@
 ; incremented to reset MMC1 reg
-reset:  
-.if INES_MAPPER = 4
-        ldy #$00
-        ldx #$06
-        stx MMC3_BANK_SELECT
-        sty MMC3_BANK_DATA
-        inx
-        iny
-        stx MMC3_BANK_SELECT
-        sty MMC3_BANK_DATA
-        lda #$00
-        stx MMC3_BANK_SELECT
-.endif
-        cld
+reset:  cld
         sei
         ldx #$00
         stx PPUCTRL
@@ -25,8 +12,10 @@ reset:
         bpl @vsyncWait2
         dex
         txs
-.if INES_MAPPER <> 4
+.if INES_MAPPER = 1
         inc reset
+.elseif INES_MAPPER = 4 
+        jsr mmc3Init
 .endif
         lda #$10
         jsr setMMC1Control
@@ -38,6 +27,26 @@ reset:
         jsr changePRGBank
         jmp initRam
 
+.if INES_MAPPER = 4
+; https://www.nesdev.org/wiki/MMC3
+mmc3Init:
+        ; 110: R6: Select 8 KB PRG ROM bank at $8000-$9FFF (or $C000-$DFFF)
+        ldx     #$06
+        ldy     #$00
+        stx     MMC3_BANK_SELECT
+        sty     MMC3_BANK_DATA
+
+        ; 111: R7: Select 8 KB PRG ROM bank at $A000-$BFFF
+        inx
+        iny
+        stx     MMC3_BANK_SELECT
+        sty     MMC3_BANK_DATA
+        lda     #$80 ; enable PRG RAM
+        sta     MMC3_PRG_RAM
+        rts
+.endif
+
+
 MMC1_PRG:
         .byte   $00,$00,$00,$00,$00,$00,$00,$00
         .byte   $00

src/util/core.asm

@@ -371,16 +371,5 @@ changePRGBank:
         sta MMC1_PRG
         lsr a
         sta MMC1_PRG
-.elseif INES_MAPPER = 4
-        asl     a
-        asl     a
-        ldx     #$06
-        stx     MMC3_BANK_SELECT
-        sta     MMC3_BANK_DATA
-        inx
-        clc
-        adc     #$01
-        stx     MMC3_BANK_SELECT
-        sta     MMC3_BANK_DATA
 .endif
         rts