make nintendo logo fly off like a rocket

Code/nintendo-out.asm

@@ -1,26 +1,116 @@
 INCLUDE "hardware.inc"
 
-SECTION "NintendoLogo", ROM0
+SECTION "Random", ROM0, ALIGN[4]
+Random:
+	db -1, 1, 2, -1, 4, 3, -2, -1, -4, 3, -1, 5, 2
+RandomEnd:
+
+HaltAndClearIF: MACRO
+	halt
+	xor a
+	ld [rIF], a
+ENDM
 
 EXPORT ScrollNintendoOut
 SECTION "Scroll Nintendo Out", ROM0
 ScrollNintendoOut:
-	ld b, 30
+
+	; wait a moment
+	ld b, 32
 .wait
-	halt
-	xor a
-	ld [rIF], a
+	HaltAndClearIF
 	dec b
 	jr nz, .wait
+	
+	; sound ON
+	ld a, $80
+	ldh [rNR52], a ; sound ON with noise channel
+	ld a, $77
+	ldh [rNR50], a ; max volume on both speakers
+	ld a, $88
+	ldh [rNR51], a ; noise channel on both speakers
+
+	; make noise
+	ld a, 0
+	ldh [rNR41], a ; set sound duration
+	ld a, $F0
+	ldh [rNR42], a ; set volume
+	ld a, $72
+	ldh [rNR43], a ; set frequency
+	ld a, $80
+	ldh [rNR44], a ; turn on
+
+	; nudge nintendo logo
+	ld d, HIGH(Random)
+	ld e, 0
+	ld b, 42
+.noise
+	HaltAndClearIF
+	HaltAndClearIF
+	ld a, [de]
+	ldh [rSCY], a
+	
+	inc e
+	ld a, e
+	cp a, RandomEnd - Random
+	jr nz, .next
+	ld e, 0
+.next
+
+	ld a, [de]
+	ldh [rSCX], a
+
+	inc e
+	ld a, e
+	cp a, RandomEnd - Random
+	jr nz, .next2
+	ld e, 0
+.next2
+	
+	dec b
+	jr nz, .noise
 
-.scrollup
-	halt
 	xor a
-	ld [rIF], a
+	ldh [rSCY], a
+	
+	; change noise
+	ld a, $62
+	ldh [rNR43], a ; set frequency
+	
+	ld b, 4 ; number of frames before reducing volume
+	ld c, 16 ; number of steps before volume is 0
+
+	; nintendo logo lift-off!
+.scrollup
+	HaltAndClearIF
+	; scroll up
 	ldh a, [rSCY]
 	inc a
 	ldh [rSCY], a
+	
+	; fade out
+	ld a, c
+	or a
+	jr z, .novolumechange
+	dec b
+	jr nz, .novolumechange
+	; decrement volume by 1
+	; see http://gbdev.gg8.se/wiki/articles/Gameboy_sound_hardware obscure behavior...
+	ld a, $08
+REPT 15 
+	ldh [rNR42], a
+ENDR
+	ld b, 4
+	dec c
+	
+.novolumechange
+	; loop until nintendo logo is out of screen
+	ldh a, [rSCY]
 	cp a, 88
 	jp nz, .scrollup
 	
+	; sound off
+	xor a
+	ldh [rNR52], a
+	
 	ret