chiptune_player: fix interrupt handler on older Apple II

chiptune_player/Makefile

@@ -8,8 +8,9 @@ all:	chiptune_player.dsk chiptune_unrolled.dsk
 $(DOS33):
 	cd ../dos33fs-utils && make
 
-chiptune_player.dsk:	CHIPTUNE_PLAYER ./krw/INTRO2.KRW
+chiptune_player.dsk:	CHIPTUNE_PLAYER ./krw/INTRO2.KRW HELLO
 	cp chiptune_empty.dsk chiptune_player.dsk
+	$(DOS33) -y chiptune_player.dsk SAVE A HELLO
 	$(DOS33) -y chiptune_player.dsk BSAVE -a 0x0C00 CHIPTUNE_PLAYER
 	$(DOS33) -y chiptune_player.dsk SAVE B ./krw/CAMOUFLAGE.KRW
 	$(DOS33) -y chiptune_player.dsk SAVE B ./krw/CHRISTMAS.KRW
@@ -53,6 +54,8 @@ chiptune_unrolled.dsk:	CHIPTUNE_UNROLLED ./krw/INTRO2.KRW
 	$(DOS33) -y chiptune_unrolled.dsk SAVE B ./krw/UNIVERSE.KRW
 	$(DOS33) -y chiptune_unrolled.dsk SAVE B ./krw/WAVE.KRW
 
+HELLO:	hello.bas
+	../asoft_basic-utils/tokenize_asoft < hello.bas > HELLO
 
 CHIPTUNE_PLAYER:	chiptune_player.o
 	ld65 -o CHIPTUNE_PLAYER chiptune_player.o -C ../linker_scripts/apple2_c00.inc

chiptune_player/hello.bas

@@ -0,0 +1,4 @@
+   5  PRINT 
+  10  PRINT "LOADING VMW CHIPTUNE PLAYER V1.2"
+  50  PRINT 
+ 100  PRINT  CHR$ (4)"BRUN CHIPTUNE_PLAYER"

chiptune_player/interrupt_handler.s

@@ -13,8 +13,14 @@
 TIME_OFFSET	EQU	13
 
 interrupt_handler:
-	pha			; save A				; 3
-				; Should we save X and Y too?
+;	pha			; save A				; 3
+				; A is saved in $45 by firmware
+	txa
+	pha			; save X
+	tya
+	pha			; save Y
+
+
 
 ;	inc	$0404		; debug (flashes char onscreen)
 
@@ -350,7 +356,14 @@ mb_clear_reg:
 
 exit_interrupt:
 
-	pla			; restore a				; 4
+;	pla			; restore a				; 4
+
+	pla
+	tay			; restore Y
+	pla
+	tax			; restore X
+	lda	$45		; restore A
+
 
 	rti			; return from interrupt			; 6