From 9da80206f8872138fcb5e51b68d87ccd78173103 Mon Sep 17 00:00:00 2001
From: Jay Oster <jay@kodewerx.org>
Date: Thu, 12 Sep 2024 15:25:00 -0700
Subject: [PATCH] Fix PRG writes in CD Logger

This code was added for FDS RAM, but it breaks PRG writes with normal
cartridge-based memory controllers.

The bug inappropriately resets (clears) the access mode bits previously
recorded when an MMIO register is written in PRG address space. For
instance, if an instruction is executed at $8000 and then some code
later writes to $8000, the instruction execution would have been
forgotten.
---
 src/debug.cpp | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/debug.cpp b/src/debug.cpp
index eef528e56..217173570 100644
--- a/src/debug.cpp
+++ b/src/debug.cpp
@@ -569,7 +569,12 @@ void LogCDData(uint8 *opcode, uint16 A, int size)
 				newDataHit = true;
 			}
 		}
-		else
+		// Unclear why the write destination's access types gets reset for FDS...
+		// See:
+		// - https://github.com/TASEmulators/fceux/commit/a4fa6225a04b5ab8d3dfca3fc9abd7190bceec85
+		// - https://github.com/TASEmulators/fceux/commit/b10b6254c3d5c9519a85cb4382cdb22846d2e394
+		// - https://github.com/TASEmulators/fceux/commit/67942accc72149ae028d58f36419b64ea8651db9?diff=unified&w=1
+		else if(GameInfo && GameInfo->type == GIT_FDS)
 		{
 			if (cdloggerdata[j] & 1)
 			{