From 9cdbc5b9812810b753aaca0738e480182b34d790 Mon Sep 17 00:00:00 2001
From: Dean Netherton <dean.netherton@gmail.com>
Date: Tue, 28 Apr 2020 19:51:15 +1000
Subject: [PATCH] SN76489: Do not play when period is overflowing

---
 Source/Apps/Tune/Tune.asm |  6 +++---
 Source/HBIOS/sn76489.asm  | 23 +++++++++++++++++++++--
 2 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/Source/Apps/Tune/Tune.asm b/Source/Apps/Tune/Tune.asm
index aa28cb95..adf29d33 100644
--- a/Source/Apps/Tune/Tune.asm
+++ b/Source/Apps/Tune/Tune.asm
@@ -2002,7 +2002,7 @@ PLAYVIAHBIOS:
 	LD	C, 0
 	LD	HL, (AYREGS+TonA)
 	ld	a, h
-	AND	$3F
+	AND	$0F
 	LD	H, A
 	RST	08
 
@@ -2027,7 +2027,7 @@ PLAYVIAHBIOS:
 	LD	C, 0
 	LD	HL, (AYREGS+TonB)
 	ld	a, h
-	AND	$3F
+	AND	$0F
 	LD	H, A
 	RST	08
 
@@ -2052,7 +2052,7 @@ PLAYVIAHBIOS:
 	LD	C, 0
 	LD	HL, (AYREGS+TonC)
 	ld	a, h
-	AND	$3F
+	AND	$0F
 	LD	H, A
 	RST	08
 
diff --git a/Source/HBIOS/sn76489.asm b/Source/HBIOS/sn76489.asm
index 8870e801..c80beff6 100644
--- a/Source/HBIOS/sn76489.asm
+++ b/Source/HBIOS/sn76489.asm
@@ -156,8 +156,12 @@ SN7_PITCH:
 	XOR	A			; SIGNAL SUCCESS
 	RET
 
-SN7_QUERY_PITCH1:
-	OR	$FF
+SN7_QUERY_PITCH1:			; REQUESTED PERIOD IS LARGER THAN THE SN76489 CAN SUPPORT
+	LD	L, $FF
+	LD	H, $FF
+	LD	(PENDING_PITCH), HL
+
+	OR	$FF			; SIGNAL FAILURE
 	RET
 
 SN7_PLAY:
@@ -165,12 +169,27 @@ SN7_PLAY:
 	AUDTRACE_D
 	AUDDEBUG("\r\n")
 
+	LD	A, (PENDING_PITCH + 1)
+	CP	$FF
+	JR	Z, SN7_PLAY1		; PERIOD IS TOO LARGE, UNABLE TO PLAY
 	CALL	SN7_APPLY_VOL
 	CALL	SN7_APPLY_PIT
 
 	XOR	A			; SIGNAL SUCCESS
 	RET
 
+SN7_PLAY1:				; TURN CHANNEL VOL TO OFF AND STOP PLAYING
+	LD	A, (PENDING_VOLUME)
+	PUSH	AF
+	LD	A, 0
+	LD	(PENDING_VOLUME), A
+	CALL	SN7_APPLY_VOL
+	POP	AF
+	LD	(PENDING_VOLUME), A
+
+	OR	$FF			; SIGNAL FAILURE
+	RET
+
 SN7_QUERY:
 	LD	A, E
 	CP	BF_SNDQ_CHCNT