From b1bb684a048e757ca8cbd4d3af851a3c811641c5 Mon Sep 17 00:00:00 2001
From: Dean Netherton <dean.netherton@gmail.com>
Date: Tue, 28 Apr 2020 18:35:20 +1000
Subject: [PATCH] SN76489: Prevent and return error code if a pitch greater
 than 03FF is attempted to be set

---
 Source/HBIOS/sn76489.asm | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/Source/HBIOS/sn76489.asm b/Source/HBIOS/sn76489.asm
index f3430b3a..8870e801 100644
--- a/Source/HBIOS/sn76489.asm
+++ b/Source/HBIOS/sn76489.asm
@@ -147,11 +147,19 @@ SN7_PITCH:
 	AUDDEBUG("SN7PIT ")
 	AUDTRACE_HL
 	AUDDEBUG("\r\n")
-	LD	(PENDING_PITCH), HL
 
+	LD	A, H
+	CP	$04
+	JP	NC, SN7_QUERY_PITCH1	; RETURN NZ IF NUMBER TOO LARGE
+
+	LD	(PENDING_PITCH), HL
 	XOR	A			; SIGNAL SUCCESS
 	RET
 
+SN7_QUERY_PITCH1:
+	OR	$FF
+	RET
+
 SN7_PLAY:
 	AUDDEBUG("SN7PLY ")
 	AUDTRACE_D
@@ -188,7 +196,6 @@ SN7_QUERY_CHCNT:
 
 SN7_QUERY_PITCH:
 	LD	HL, (PENDING_PITCH)
-
 	XOR	A
 	RET