megademo: add interrupt-driven music during mode7 segment

megademo/Makefile

@@ -30,6 +30,7 @@ MEGADEMO:	megademo.o
 megademo.o:	megademo.s \
 	zp.inc hardware.inc \
 	gr_hline.s gr_offsets.s vapor_lock.s delay_a.s wait_keypress.s \
+	mockingboard.s \
 	c64_opener.s c64.img.lz4 \
 	falling_apple.s apple_40_96.inc \
 	starring.s starring1.inc starring2.inc starring3.img.lz4\
@@ -61,7 +62,7 @@ megaload.o:      megaload.s
 MUSIC.1000:	music_1000.o
 	ld65 -o MUSIC.1000 music_1000.o -C ../linker_scripts/apple2_1000.inc
 
-music_1000.o:	music_1000.s
+music_1000.o:	music_1000.s mockingboard.s
 	ca65 -o music_1000.o music_1000.s -l music_1000.lst
 
 ####

megademo/mockingboard.s

@@ -101,7 +101,6 @@ reset_ay_right:
 	; Setup initial conditions
 	;=========================
 
-
 	; 7: ENABLE
 	ldx	#7
 	lda	#$38			; noise disabled, ABC enabled
@@ -120,7 +119,7 @@ reset_ay_right:
 	sta	$03ff
 
 	;============================
-	; Enable 50Hz clock on 6522
+	; Enable 60Hz clock on 6522
 	;============================
 
 	sei			; disable interrupts just in case
@@ -134,13 +133,14 @@ reset_ay_right:
 	sta	$C40D		; IFR: 1100, enable interrupt on timer one oflow
 	sta	$C40E		; IER: 1100, enable timer one interrupt
 
-	lda	#$1A
+	lda	#$1a
 	sta	$C404		; write into low-order latch
 	lda	#$41
 	sta	$C405		; write into high-order latch,
 				; load both values into counter
 				; clear interrupt and start counting
 
+	; 9c40 / 1e6 = .040s, 25Hz
 	; 4fe7 / 1e6 = .020s, 50Hz
 	; 411a / 1e6 = .016s, 60Hz
 
@@ -148,6 +148,7 @@ reset_ay_right:
 
 interrupt_handler:
 	; A saved by firmware in $45
+	sta	$45
 	txa
 	pha			; save X
 	tya
@@ -161,6 +162,8 @@ interrupt_handler:
 	tax			; restore X
 	lda	$45		; restore A
 
+	bit     $C404           ; clear 6522 interrupt by reading T1C-L ; 4
+
 	rti			; return from interrupt                 ; 6
 
 

megademo/mode7.s

@@ -62,6 +62,8 @@ island_flying_directions:
 
 mode7_flying:
 
+	cli	; enable interrupts (play music)
+
 	;================================
 	; one-time setup
 	;================================
@@ -153,6 +155,7 @@ done_key:
 done_mode7:
 	bit	KEYRESET
 	; done
+	sei			; disable interrupts
 	rts
 
 check_up:

megademo/takeoff.s

@@ -140,6 +140,7 @@ to_begin_loop:
 
 	; 3116 - 1038 (music) = 2078
 
+	jsr	play_music
 
 	; Try X=5 Y=67 cycles=2078
 	; Try X=11 Y=51 cycles=3112 R4