audio partly working

dither4.s

@@ -1,13 +1,11 @@
 SAVMSC = $58
-;SDMCTL = $22F
-;SDLSTL = $230
-;SDLSTH = $231
 COLPF0 = $D016
 COLPF1 = $D017
 COLPF2 = $D018
 COLPF3 = $D019
 COLBK = $D01A
 
+AUDC1 = $D201
 DMACTL = $D400
 DLISTL = $D402
 DLISTH = $D403
@@ -24,10 +22,14 @@ temp1 = temp1l
 temp2l = $82
 temp2h = $83
 temp2 = temp2l
+sample_ptrl = $84
+sample_ptrh = $85
+sample_ptr = sample_ptrl
 
 height = 192
 bytes_per_line = 40
 pages_per_frame = 32
+lines_per_frame = 262
 
 .data
 
@@ -35,6 +37,8 @@ pages_per_frame = 32
 .import palette2
 .import palette3
 .import bitmap
+.import audio_samples
+.import audio_samples_end
 
 displaylist:
     ; 24 lines overscan
@@ -70,18 +74,24 @@ displaylist:
     lda #.hibyte(bitmap)
     sta temp1h
     lda #.lobyte(framebuffer)
-    sta temp2h
+    sta temp2l
     lda #.hibyte(framebuffer)
     sta temp2h
     jsr copy_half_frame
 
     ; Second half of bitmap has to be separately aligned
     lda #.lobyte(framebuffer2)
-    sta temp2h
+    sta temp2l
     lda #.hibyte(framebuffer2)
     sta temp2h
     jsr copy_half_frame
 
+    ; Set up the audio sample buffer
+    lda #.lobyte(audio_samples)
+    sta sample_ptrl
+    lda #.hibyte(audio_samples)
+    sta sample_ptrh
+
     ; Disable display DMA
     lda #$00
     sta DMACTL
@@ -106,40 +116,102 @@ wait_vblank:
     lda #$22
     sta DMACTL
 
-wait_loop:
-    sta WSYNC
+; Wait for the next even scanline (VCOUNT is scan line / 2, so look for a change)
 wait_start:
     lda VCOUNT
-    cmp #15
-    bne wait_loop
-    ldy #0
+    sta temp1
+wait_loop:
+    lda VCOUNT
+    cmp temp1
+    beq wait_loop
 
 each_scanline:
-    tya
-    pha
-
-    lda palette1,y
-    pha
-    ldx palette2,y
-    lda palette3,y
+    lda VCOUNT
+    ; Resynchronize the scanline counter
+    ; it'll fire on unused lines, but harmlessly
+    clc
+    sbc #15
+    asl
     tay
-    pla
 
-    ; Wait for horizontal blank
-    sta WSYNC
+    .macro audio_prep
+        ; audio sample; low nybble
+        ldx #0
+        lda (sample_ptr,x)
+        sta temp2
 
-    ; Update color registers as fast as possible
-    sta COLPF0
-    stx COLPF1
-    sty COLPF2
+        ; high nybble
+        lsr a
+        lsr a
+        lsr a
+        lsr a
+        ; set the volume-only bit
+        ora #$10
+        pha
 
-    pla
-    tay
+        ; low nybble
+        lda temp2
+        and #$0f
+        ; set the volume-only bit
+        ora #$10
+        pha
+    .endmacro
+
+    .macro audio_inc
+        ; Increment sample ptr
+        clc
+        lda sample_ptrl
+        adc #1
+        sta sample_ptrl
+        lda sample_ptrh
+        adc #0
+        sta sample_ptrh
+
+        lda sample_ptrh
+        cmp #.hibyte(audio_samples_end)
+        bne audio_cont
+        lda sample_ptrl
+        cmp #.lobyte(audio_samples_end)
+        bne audio_cont
+        lda #.lobyte(audio_samples)
+        sta sample_ptrl
+        lda #.hibyte(audio_samples)
+        sta sample_ptrh
+
+        audio_cont:
+    .endmacro
+
+    .macro inner_scanline
+        ; Leisurely memory fetches
+        lda palette1,y
+        pha
+        ldx palette2,y
+        lda palette3,y
+        tay
+        pla
+
+        ; Wait for horizontal blank
+        sta WSYNC
+
+        ; Update color registers as fast as possible
+        sta COLPF0
+        stx COLPF1
+        sty COLPF2
+        
+        ; Audio sample
+        pla
+        sta AUDC1
+    .endmacro
+
+    audio_prep
+    inner_scanline
+
+    audio_inc
     iny
-    cpy #height
-    bne each_scanline
+    inner_scanline
 
-    jmp wait_start    
+    ;jmp wait_start    
+    jmp each_scanline
 
 .endproc