Merge pull request #115 from negative-seven/master

Add dev flag to swap pulse wave duty cycles

Author: kirjavascript

src/audio.asm

@@ -73,6 +73,12 @@ copyToApuChannel:
         ldy #$00
 @copyByte:
         lda (AUDIOTMP3),y
+.if SWAP_DUTY_CYCLES
+        cpy #0
+        bne @notFirstByte
+        jsr swapDutyCycles
+@notFirstByte:
+.endif
         sta (AUDIOTMP1),y
         iny
         tya
@@ -465,6 +471,9 @@ soundEffectSlot1_chirpChirpPlaying:
         and #$03
         tay
         lda soundEffectSlot1_chirpChirpSq1Vol_table,y
+.if SWAP_DUTY_CYCLES
+        jsr swapDutyCycles
+.endif
         sta SQ1_VOL
         inc soundEffectSlot1SecondaryCounter
         lda soundEffectSlot1SecondaryCounter
@@ -615,6 +624,10 @@ LE442:  jsr copyToSq1Channel
         sta SQ1_LO
         ldy soundEffectSlot1SecondaryCounter
         lda sq1vol_unknown2_table,y
+.if SWAP_DUTY_CYCLES
+        jsr swapDutyCycles
+        tay ; set z flag based on a; y can be safely clobbered
+.endif
         sta SQ1_VOL
         bne LE46F
         lda soundEffectSlot1Playing
@@ -1062,6 +1075,9 @@ updateMusicFrame_setChanVol:
         bne @ret
         tya
         ldy musicChannelOffset
+.if SWAP_DUTY_CYCLES
+        jsr swapDutyCycles
+.endif
         sta SQ1_VOL,y
 @ret:   rts
 
@@ -1342,6 +1358,9 @@ updateMusicFrame_updateChannel:
 @useDirectVolume:
         lda AUDIOTMP1
 @setMmio:
+.if SWAP_DUTY_CYCLES
+        jsr swapDutyCycles
+.endif
         sta SQ1_VOL,y
         lda musicStagingSq1Sweep,x
         sta SQ1_SWEEP,y
@@ -1454,6 +1473,15 @@ musicGetNextInstructionByte:
         lda (musicChanTmpAddr),y
         rts
 
+.if SWAP_DUTY_CYCLES
+; input a: byte to be written to $4000 or $4004. output a: the same byte with the duty cycle index mapped from (0, 1, 2, 3) to (0, 2, 1, 3), counteracting the behavior of some clone consoles
+swapDutyCycles:
+        cmp #%01000000
+        bmi @ret ; branch if upper bits are not %01 or %10
+        eor #%11000000 ; swap between %01 and %10
+@ret:   rts
+.endif
+
 musicChanVolControlTable:
 noteToWaveTable:
 noteDurationTable:

src/constants.asm

@@ -27,6 +27,7 @@ NO_SFX := 0
 NO_MENU := 0
 ALWAYS_CURTAIN := 0
 QUAL_BOOT := 0
+SWAP_DUTY_CYCLES := 0 ; counters the duty cycle swap present in some clone consoles
 
 INITIAL_CUSTOM_LEVEL := 29
 INITIAL_LINECAP_LEVEL := 39