From 50fc4091f703d3944812282b40958de8d700de41 Mon Sep 17 00:00:00 2001
From: ekeeke <ekeeke31@gmail.com>
Date: Wed, 23 Sep 2026 22:54:08 +0200
Subject: [PATCH] [Core/CD] minor Main-CPU/Sub-CPU synchronization optimization

---
 core/cd_hw/scd.c | 10 ++++++----
 core/mem68k.c    | 10 ++++++----
 2 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/core/cd_hw/scd.c b/core/cd_hw/scd.c
index 187753f2..708f4f03 100644
--- a/core/cd_hw/scd.c
+++ b/core/cd_hw/scd.c
@@ -504,14 +504,16 @@ static void s68k_poll_sync(unsigned int reg_mask)
 
 static void m68k_sync(void)
 {
+  /* check MAIN-CPU is still running */
   if (!m68k.stopped)
   {
-    /* relative MAIN-CPU cycle counter */
-    unsigned int cycles = (s68k.cycles * MCYCLES_PER_LINE) / SCYCLES_PER_LINE;
-
-    /* sync MAIN-CPU with SUB-CPU (only if MAIN-CPU execution frame is finished, to prevent recursive execution) */
+    /* check MAIN-CPU execution frame is finished (to prevent recursive execution) */
     if (!m68k.cycle_end)
     {
+      /* relative MAIN-CPU cycle counter */
+      unsigned int cycles = (s68k.cycles * MCYCLES_PER_LINE) / SCYCLES_PER_LINE;
+
+      /* sync MAIN-CPU with SUB-CPU */
       m68k_run(cycles);
     }
   }
diff --git a/core/mem68k.c b/core/mem68k.c
index 0b0354c8..6dd6b004 100644
--- a/core/mem68k.c
+++ b/core/mem68k.c
@@ -302,14 +302,16 @@ static void m68k_poll_sync(unsigned int reg_mask)
 
 static void s68k_sync(void)
 {
+  /* check SUB-CPU is still running */
   if (!s68k.stopped)
   {
-    /* relative SUB-CPU cycle counter */
-    unsigned int cycles = (m68k.cycles * SCYCLES_PER_LINE) / MCYCLES_PER_LINE;
-
-    /* sync SUB-CPU with MAIN-CPU (only if SUB-CPU execution frame is finished, to prevent recursive execution) */
+    /* check SUB-CPU execution frame is finished (to prevent recursive execution) */
     if (!s68k.cycle_end)
     {
+      /* relative SUB-CPU cycle counter */
+      unsigned int cycles = (m68k.cycles * SCYCLES_PER_LINE) / MCYCLES_PER_LINE;
+
+      /* sync SUB-CPU with MAIN-CPU */
       s68k_run(cycles);
     }
   }