From 97d4c052d042e9c5b56d638070f13c43ee6a7cb8 Mon Sep 17 00:00:00 2001
From: negative <negativeExponent@users.noreply.github.com>
Date: Sun, 6 Mar 2022 08:48:02 +0800
Subject: [PATCH] FDS: Improve IRQ emulation

Fix https://github.com/TASEmulators/fceux/issues/468
---
 src/fds.cpp | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/src/fds.cpp b/src/fds.cpp
index 3fc4ee92..35924a4a 100644
--- a/src/fds.cpp
+++ b/src/fds.cpp
@@ -223,16 +223,18 @@ void FCEU_FDSSelect(void)
 	FCEU_DispMessage("Disk %d Side %c Selected", 0, SelectDisk >> 1, (SelectDisk & 1) ? 'B' : 'A');
 }
 
+#define IRQ_Repeat  (IRQa & 0x01)
+#define IRQ_Enabled (IRQa & 0x02)
+
 static void FDSFix(int a) {
-	if ((IRQa & 2) && IRQCount) {
+	if ((IRQa & IRQ_Enabled) && IRQCount) {
 		IRQCount -= a;
 		if (IRQCount <= 0) {
-			if (!(IRQa & 1)) {
-				IRQa &= ~2;
-				IRQCount = IRQLatch = 0;
-			} else
-				IRQCount = IRQLatch;
+			IRQCount = IRQLatch;
 			X6502_IRQBegin(FCEU_IQEXT);
+			if (!(IRQa & IRQ_Repeat)) {
+				IRQa &= ~IRQ_Enabled;
+			}
 		}
 	}
 	if (DiskSeekIRQ > 0) {