whoops it's 16 levels not 8 :D

Makefile

@@ -1,3 +1,5 @@
+.FAKE : all test clean
+
 all : rickroll.xex
 
 # reminder: $< is input
@@ -9,8 +11,11 @@ all : rickroll.xex
 %.o : %.s
 	ca65 -v -t atari -o $@ $<
 
-%.xex : %.o mono8.o atari-asm-xex.cfg
-	ld65 -v -C ./atari-asm-xex.cfg -o $@ mono8.o $<
+%.xex : %.o mono16.o atari-asm-xex.cfg
+	ld65 -v -C ./atari-asm-xex.cfg -o $@ mono16.o $<
+
+test : all
+	atari800 rickroll.xex
 
 clean :
 	rm -f *.xex

mono16.s

@@ -0,0 +1,159 @@
+SAVMSC = $58
+VDSLST = $200
+VDSLSTL = $200
+VDSLSTH = $201
+COLPF0 = $D016
+COLPF1 = $D017
+COLPF2 = $D018
+COLPF3 = $D019
+COLBK = $D01A
+
+AUDC1 = $D201
+DMACTL = $D400
+DLISTL = $D402
+DLISTH = $D403
+WSYNC = $D40A
+VCOUNT = $D40B
+NMIEN = $D40E
+
+temp1l = $80
+temp1h = $81
+temp1 = temp1l
+temp2l = $82
+temp2h = $83
+temp2 = temp2l
+sample_ptrl = $84
+sample_ptrh = $85
+sample_ptr = sample_ptrl
+scanline = $86
+frame_counter = $89
+
+;height = 160
+height = 192
+bytes_per_line = 40
+pages_per_frame = 32
+lines_per_frame = 262
+;scanline_offset = 31 + (40 - 24) / 2
+scanline_offset = 30
+scanline_max = (lines_per_frame - scanline_offset) / 2
+
+.data
+
+.import frame1_top
+.import frame1_bottom
+.import frame1_palette1_even
+.import frame1_palette1_odd
+.import frame1_palette2_even
+.import frame1_palette2_odd
+.import frame1_palette3_even
+.import frame1_palette3_odd
+.import displaylist
+
+.code
+
+.export start
+
+.proc start
+    ; Disable display DMA
+    lda #$00
+    sta DMACTL
+
+    ; Disable VBI and DLI but allow Reset
+    lda #$20
+    sta NMIEN
+
+    ; Set up the display list
+    lda #.lobyte(displaylist)
+    sta DLISTL
+    lda #.hibyte(displaylist)
+    sta DLISTH
+
+    ; Set up the DLI handler
+    lda #.lobyte(dli_handler)
+    sta VDSLSTL
+    lda #.hibyte(dli_handler)
+    sta VDSLSTH
+
+    ; Disable VBI but allow Reset and DLI
+    lda #$a0
+    sta NMIEN
+
+    ; Manually wait for first scan line
+wait_vblank:
+    sta WSYNC
+    lda VCOUNT
+    bne wait_vblank
+
+    ; Re-enable display DMA
+    lda #$22
+    sta DMACTL
+
+wait_start:
+    ; Wait for the vblank
+    ; Resynchronize the scanline counter
+wait_loop:
+    ldy VCOUNT    ; 4 cycles
+    bne wait_loop ; 2 cycles
+
+    .macro inner_scanline frame_offset, line_offset
+        ; Y should be VCOUNT at entry
+        ; it'll fire on unused lines, but harmlessly
+        ;ldy scanline ; 3 cyc
+        ;inc scanline ; 5 cyc
+
+        ; 23-26 cycles before break
+        ; Leisurely memory fetches
+        lda frame1_palette1_even + frame_offset + line_offset - scanline_offset / 2,y ; 4/5 @FIXME alternate
+        pha                                                                           ; 3
+        ldx frame1_palette2_even + frame_offset + line_offset - scanline_offset / 2,y ; 4/5
+        lda frame1_palette3_even + frame_offset + line_offset - scanline_offset / 2,y ; 4/5
+        tay                                                                           ; 2
+        pla                                                                           ; 3
+        ; Wait for horizontal blank
+        sta WSYNC                                                                     ; 4
+
+        ; 12 cycles after break
+        ; Update color registers as fast as possible
+        sta COLPF0 ; 4
+        stx COLPF1 ; 4
+        sty COLPF2 ; 4
+    .endmacro
+
+    .macro run_frame frame_offset
+    .scope
+        ; each scanline is 228 color clocks
+        ; that's 114 CPU cycles
+        ; minus 41-43 for DMA leaves 71-73 clock cycles per line
+
+    each_scanline_pair:
+        sty scanline ; 3 cycles
+        inner_scanline frame_offset, 0 ; 23-26 cycles before break, 12 cycles after
+
+        ldy scanline   ; 3 cycles
+        inner_scanline frame_offset, 128 ; 23-26 cycles before break, 12 cycles after
+
+        ; pair cleanup: 6 cycles
+        ldy VCOUNT             ; 4 cycles
+        bne each_scanline_pair ; 2 cycles
+
+        ; frame cleanup: 11 cycles
+        lda frame_counter ; 3 cycles
+        eor #1            ; 2 cycles
+        sta frame_counter ; 3 cycles
+        ;jmp wait_start    ; 3 cycles
+        jmp each_frame    ; 3 cycles
+    .endscope
+    .endmacro
+
+each_frame:
+run_frame1:
+    run_frame 0
+
+.endproc
+
+
+.proc dli_handler
+    lda #0
+    sta frame_counter
+    rti
+.endproc