anchor.diff:      (pokeword (label 'music-start) mptr) ; Set initial playback pointer.
       (rts))
   
  -  (procedure reset
  +  (procedure reset                      ; ------------------------------------
       (sei)
       (cld)
       (poke #b00010000 +ppu-cr1+)         ; NMI off during init.
  
positive.code:     (jsr 'update-sprites)
  
      ;; Switch pattern tables mid-frame:
      (emit-delay (+ (* 114 107) 30))
      (lda top-ntaddr)
      (eor (imm #b10010000))            ; Invert pattern bank.
      (sta (mem +ppu-cr1+))
  
negative.code:     ;; the sprite tables, and if I didn't shut it off, you'd notice
      ;; the background stopped waving.
      (loop repeat 10 do (nop))           ; Realign with hblank.. again.
      ;; Actually, leave the sprites on, otherwise they'll be disabled
      ;; during the DMA transfer, which is unwise.
      (poke #x10 +ppu-cr2+)
  
      (rts))
  
  