From 5d46298dcc32a036c5d4d3214325726f8b7fbfc9 Mon Sep 17 00:00:00 2001
From: tomcw <tomcw@users.noreply.github.com>
Date: Sun, 17 Jan 2021 19:51:25 +0000
Subject: [PATCH] Mockingboard: support AY-3-8913 read

---
 source/AY8910.cpp       | 45 +++++++++++++++++++++++++++++++++++++++++
 source/AY8910.h         |  3 +++
 source/Mockingboard.cpp |  1 +
 3 files changed, 49 insertions(+)

diff --git a/source/AY8910.cpp b/source/AY8910.cpp
index 3a0f0716..fe8fa5d4 100644
--- a/source/AY8910.cpp
+++ b/source/AY8910.cpp
@@ -709,6 +709,47 @@ void CAY8910::sound_ay_overlay( void )
   }
 }
 
+BYTE CAY8910::sound_ay_read( int reg )
+{
+	reg &= 15;
+
+	BYTE val = 0;
+	bool got = false;
+
+	if (ay_change_count)
+	{
+		for (int i=ay_change_count-1; i>=0; i--)
+		{
+			if (ay_change[i].reg == reg)
+			{
+				val = ay_change[i].val;	// return the most recently written reg's value
+				got = true;
+			}
+		}
+	}
+
+	if (!got)
+		val = sound_ay_registers[reg];
+
+	switch (reg & 15)
+	{
+	case 1:
+	case 3:
+	case 5:
+	case 13:
+		val &= 15;
+		break;
+	case 6:
+	case 8:
+	case 9:
+	case 10:
+		val &= 31;
+		break;
+	}
+
+	return val;
+}
+
 // AppleWin:TC  Holding down ScrollLock will result in lots of AY changes /ay_change_count/
 //              - since sound_ay_overlay() is called to consume them.
 
@@ -1145,6 +1186,10 @@ bool CAY8910::LoadSnapshot(YamlLoadHelper& yamlLoadHelper, const std::string& su
 static CAY8910 g_AY8910[MAX_8910];
 static unsigned __int64 g_uLastCumulativeCycles = 0;
 
+BYTE AYReadReg(int chip, int r)
+{
+	return g_AY8910[chip].sound_ay_read(r);
+}
 
 void _AYWriteReg(int chip, int r, int v)
 {
diff --git a/source/AY8910.h b/source/AY8910.h
index 85b246b3..0dc272b1 100644
--- a/source/AY8910.h
+++ b/source/AY8910.h
@@ -2,6 +2,8 @@
 
 #define MAX_8910 4
 
+BYTE AYReadReg(int chip, int r);	// TC
+
 //-------------------------------------
 // MAME interface
 
@@ -40,6 +42,7 @@ public:
 
 	void sound_ay_init( void );
 	void sound_init( const char *device );
+	BYTE sound_ay_read( int reg );	// TC
 	void sound_ay_write( int reg, int val, libspectrum_dword now );
 	void sound_ay_reset( void );
 	void sound_frame( void );
diff --git a/source/Mockingboard.cpp b/source/Mockingboard.cpp
index 5c3dd19d..50caae1d 100644
--- a/source/Mockingboard.cpp
+++ b/source/Mockingboard.cpp
@@ -321,6 +321,7 @@ static void AY8910_Write(BYTE nDevice, BYTE /*nReg*/, BYTE nValue, BYTE nAYDevic
 					break;
 
 				case AY_READ:		// 5: READ FROM PSG (need to set DDRA to input)
+					pMB->sy6522.ORA = AYReadReg(nDevice+2*nAYDevice, pMB->nAYCurrentRegister) & (pMB->sy6522.DDRA ^ 0xff);
 					break;
 
 				case AY_WRITE:		// 6: WRITE TO PSG