From e4fbeebfa7c47d8ab6192c397f3e04c8705657b3 Mon Sep 17 00:00:00 2001
From: Adrian Conlon <98398945+AdrianConlon@users.noreply.github.com>
Date: Sun, 31 Dec 2023 14:32:16 +0000
Subject: [PATCH] Correct problem in page boundary condition for M6502.

---
 M6502/inc/mos6502.h   | 1 +
 M6502/src/mos6502.cpp | 8 +++++++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/M6502/inc/mos6502.h b/M6502/inc/mos6502.h
index 970e01e..cec6105 100644
--- a/M6502/inc/mos6502.h
+++ b/M6502/inc/mos6502.h
@@ -188,6 +188,7 @@ namespace EightBit {
 
 		void sta_AbsoluteX() noexcept;
 		void sta_AbsoluteY() noexcept;
+		void sta_IndirectIndexedY() noexcept;
 
 		uint8_t x = 0;		// index register X
 		uint8_t y = 0;		// index register Y
diff --git a/M6502/src/mos6502.cpp b/M6502/src/mos6502.cpp
index dfb9c24..b520650 100644
--- a/M6502/src/mos6502.cpp
+++ b/M6502/src/mos6502.cpp
@@ -266,7 +266,7 @@ int EightBit::MOS6502::execute() noexcept {
 	case 0x8f:	memoryWrite(Address_Absolute(), A() & X());					break;	// *SAX (absolute)
 
 	case 0x90:	branch(!carry());											break;	// BCC (relative)
-	case 0x91:	memoryRead(Address_IndirectIndexedY().first); memoryWrite(A()); break;	// STA (indirect indexed Y)
+	case 0x91:	sta_IndirectIndexedY();										break;	// STA (indirect indexed Y)
 	case 0x92:																break;
 	case 0x93:																break;
 	case 0x94:	memoryWrite(Address_ZeroPageX(), Y());						break;	// STY (zero page, X)
@@ -757,3 +757,9 @@ void EightBit::MOS6502::sta_AbsoluteY() noexcept {
 	getBytePaged(page, address.low);
 	memoryWrite(address, A());
 }
+
+void EightBit::MOS6502::sta_IndirectIndexedY() noexcept {
+	const auto [address, page] = Address_IndirectIndexedY();
+	getBytePaged(page, address.low);	// Possible fixup for page boundary crossing
+	memoryWrite(address, A());
+}