From 66775b2c4ee4a989d07dd07e59106ef73167731e Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Thu, 23 Jun 2022 12:46:51 -0400
Subject: [PATCH] Always consume a second cycle in 16-bit mode.

---
 .../65816/Implementation/65816Implementation.hpp | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/Processors/65816/Implementation/65816Implementation.hpp b/Processors/65816/Implementation/65816Implementation.hpp
index 86e561445..bc4ae8bc8 100644
--- a/Processors/65816/Implementation/65816Implementation.hpp
+++ b/Processors/65816/Implementation/65816Implementation.hpp
@@ -300,8 +300,12 @@ template <typename BusHandler, bool uses_ready_line> void Processor<BusHandler,
 					data_address_ = instruction_buffer_.value + registers_.x.full + registers_.data_bank;
 					incorrect_data_address_ = ((data_address_ & 0x00ff) | (instruction_buffer_.value & 0xff00)) + registers_.data_bank;
 
-					// If the incorrect address isn't actually incorrect, skip its usage.
-					if(operation == OperationConstructAbsoluteXRead && data_address_ == incorrect_data_address_) {
+					// "Add 1 cycle for indexing across page boundaries, or write, or X=0"
+					// (i.e. don't add 1 cycle if x = 1 and this is a read, and a page boundary wasn't crossed)
+					if(
+						operation == OperationConstructAbsoluteXRead &&
+						data_address_ == incorrect_data_address_ &&
+						registers_.mx_flags[1]) {
 						++next_op_;
 					}
 					data_address_increment_mask_ = 0xff'ff'ff;
@@ -312,8 +316,12 @@ template <typename BusHandler, bool uses_ready_line> void Processor<BusHandler,
 					data_address_ = instruction_buffer_.value + registers_.y.full + registers_.data_bank;
 					incorrect_data_address_ = (data_address_ & 0xff) + (instruction_buffer_.value & 0xff00) + registers_.data_bank;
 
-					// If the incorrect address isn't actually incorrect, skip its usage.
-					if(operation == OperationConstructAbsoluteYRead && data_address_ == incorrect_data_address_) {
+					// "Add 1 cycle for indexing across page boundaries, or write, or X=0"
+					// (i.e. don't add 1 cycle if x = 1 and this is a read, and a page boundary wasn't crossed)
+					if(
+						operation == OperationConstructAbsoluteYRead &&
+						data_address_ == incorrect_data_address_ &&
+						registers_.mx_flags[1]) {
 						++next_op_;
 					}
 					data_address_increment_mask_ = 0xff'ff'ff;