From 9763b2928a9a294a1bb2b4cb0af1e7626b64ef22 Mon Sep 17 00:00:00 2001
From: Dirk Best <mail@dirk-best.de>
Date: Sun, 5 Mar 2017 18:06:18 +0100
Subject: [PATCH] ay8910: Add a write handler for the case of bc1=a0 and bc2=a1

---
 src/devices/sound/ay8910.cpp | 18 ++++++++++++++++++
 src/devices/sound/ay8910.h   |  7 +++++--
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/src/devices/sound/ay8910.cpp b/src/devices/sound/ay8910.cpp
index a3979b70bf6..4da686b0cb4 100644
--- a/src/devices/sound/ay8910.cpp
+++ b/src/devices/sound/ay8910.cpp
@@ -1119,6 +1119,24 @@ WRITE8_MEMBER( ay8910_device::data_w )
 #endif
 }
 
+WRITE8_MEMBER( ay8910_device::write )
+{
+	switch (offset & 3)
+	{
+	case 0: // latch address
+		address_w(space, 0, data);
+		break;
+	case 1: // inactive
+		break;
+	case 2: // write to psg
+		data_w(space, 0, data);
+		break;
+	case 3: // latch address
+		address_w(space, 0, data);
+		break;
+	}
+}
+
 WRITE8_MEMBER( ay8910_device::reset_w )
 {
 	ay8910_reset_ym();
diff --git a/src/devices/sound/ay8910.h b/src/devices/sound/ay8910.h
index a46bef62ffc..bc970338385 100644
--- a/src/devices/sound/ay8910.h
+++ b/src/devices/sound/ay8910.h
@@ -1,4 +1,4 @@
-// license:BSD-3-Clause
+ // license:BSD-3-Clause
 // copyright-holders:Couriersud
 #pragma once
 
@@ -126,6 +126,9 @@ public:
 	/* use this when BC1 == !A0; here, BC1=0 selects 'latch address' and BC1=1 selects 'data' */
 	DECLARE_WRITE8_MEMBER( address_data_w );
 
+	// bc1=a0, bc2=a1
+	virtual DECLARE_WRITE8_MEMBER(write);
+
 	void set_volume(int channel,int volume);
 	void ay_set_clock(int clock);
 
@@ -227,7 +230,7 @@ public:
 
 	/* AY8914 handlers needed due to different register map */
 	DECLARE_READ8_MEMBER( read );
-	DECLARE_WRITE8_MEMBER( write );
+	virtual DECLARE_WRITE8_MEMBER( write ) override;
 };
 
 extern const device_type AY8914;