From cae62cd6756905ee98175699f02ee13a93a3ea3d Mon Sep 17 00:00:00 2001
From: ekeeke <ekeeke31@gmail.com>
Date: Sat, 23 Mar 2019 13:55:44 +0100
Subject: [PATCH] [Core/CD] fixed Main-CPU/Sub-CPU synchronization edge case

---
 core/cd_hw/scd.c | 14 +++++++++++++-
 core/mem68k.c    | 28 ++++++++++++++++++++++++++--
 core/mem68k.h    |  2 +-
 3 files changed, 40 insertions(+), 4 deletions(-)

diff --git a/core/cd_hw/scd.c b/core/cd_hw/scd.c
index 9f1b022..42192c2 100644
--- a/core/cd_hw/scd.c
+++ b/core/cd_hw/scd.c
@@ -445,10 +445,16 @@ static void s68k_poll_sync(unsigned int reg_mask)
   /* relative MAIN-CPU cycle counter */
   unsigned int cycles = (s68k.cycles * MCYCLES_PER_LINE) / SCYCLES_PER_LINE;
 
-  /* sync MAIN-CPU with SUB-CPU */
   if (!m68k.stopped)
   {
+    /* save current MAIN-CPU end cycle count (recursive execution is possible) */
+    int end_cycle = m68k.cycle_end;
+
+    /* sync MAIN-CPU with SUB-CPU */
     m68k_run(cycles);
+
+    /* restore MAIN-CPU end cycle count */
+    m68k.cycle_end = end_cycle;
   }
 
   /* MAIN-CPU idle on register polling ? */
@@ -669,8 +675,14 @@ static unsigned int scd_read_word(unsigned int address)
       /* relative MAIN-CPU cycle counter */
       unsigned int cycles = (s68k.cycles * MCYCLES_PER_LINE) / SCYCLES_PER_LINE;
 
+      /* save current MAIN-CPU end cycle count (recursive execution is possible) */
+      int end_cycle = m68k.cycle_end;
+
       /* sync MAIN-CPU with SUB-CPU (Mighty Morphin Power Rangers) */
       m68k_run(cycles);
+
+      /* restore MAIN-CPU end cycle count */
+      m68k.cycle_end = end_cycle;
     }
 
     s68k_poll_detect(3 << (address & 0x1e));
diff --git a/core/mem68k.c b/core/mem68k.c
index 9099e49..23f0d67 100644
--- a/core/mem68k.c
+++ b/core/mem68k.c
@@ -3,7 +3,7 @@
  *  Main 68k bus handlers
  *
  *  Copyright (C) 1998-2003  Charles Mac Donald (original code)
- *  Copyright (C) 2007-2017  Eke-Eke (Genesis Plus GX)
+ *  Copyright (C) 2007-2019  Eke-Eke (Genesis Plus GX)
  *
  *  Redistribution and use of this code or any derivative works are permitted
  *  provided that the following conditions are met:
@@ -268,10 +268,16 @@ static void m68k_poll_sync(unsigned int reg_mask)
   /* relative SUB-CPU cycle counter */
   unsigned int cycles = (m68k.cycles * SCYCLES_PER_LINE) / MCYCLES_PER_LINE;
 
-  /* sync SUB-CPU with MAIN-CPU */
   if (!s68k.stopped)
   {
+    /* save current SUB-CPU end cycle count (recursive execution is possible) */
+    int end_cycle = s68k.cycle_end;
+
+    /* sync SUB-CPU with MAIN-CPU */
     s68k_run(cycles);
+
+    /* restore SUB-CPU end cycle count */
+    s68k.cycle_end = end_cycle;
   }
 
   /* SUB-CPU idle on register polling ? */
@@ -354,8 +360,14 @@ unsigned int ctrl_io_read_byte(unsigned int address)
             /* relative SUB-CPU cycle counter */
             unsigned int cycles = (m68k.cycles * SCYCLES_PER_LINE) / MCYCLES_PER_LINE;
 
+            /* save current SUB-CPU end cycle count (recursive execution is possible) */
+            int end_cycle = s68k.cycle_end;
+
             /* sync SUB-CPU with MAIN-CPU (Dracula Unleashed w/ Sega CD Model 2 Boot ROM) */
             s68k_run(cycles);
+
+            /* restore SUB-CPU end cycle count */
+            s68k.cycle_end = end_cycle;
           }
 
           m68k_poll_detect(1<<0x0f);
@@ -527,8 +539,14 @@ unsigned int ctrl_io_read_word(unsigned int address)
               /* relative SUB-CPU cycle counter */
               unsigned int cycles = (m68k.cycles * SCYCLES_PER_LINE) / MCYCLES_PER_LINE;
 
+              /* save current SUB-CPU end cycle count (recursive execution is possible) */
+              int end_cycle = s68k.cycle_end;
+
               /* sync SUB-CPU with MAIN-CPU (Soul Star) */
               s68k_run(cycles);
+
+              /* restore SUB-CPU end cycle count */
+              s68k.cycle_end = end_cycle;
             }
 
             m68k_poll_detect(3 << (index - 0x10));
@@ -646,8 +664,14 @@ void ctrl_io_write_byte(unsigned int address, unsigned int data)
                   /* relative SUB-CPU cycle counter */
                   unsigned int cycles = (m68k.cycles * SCYCLES_PER_LINE) / MCYCLES_PER_LINE;
 
+                  /* save current SUB-CPU end cycle count (recursive execution is possible) */
+                  int end_cycle = s68k.cycle_end;
+
                   /* sync SUB-CPU with MAIN-CPU (Earnest Evans, Fhey Area) */
                   s68k_run(cycles);
+
+                  /* restore SUB-CPU end cycle count */
+                  s68k.cycle_end = end_cycle;
                 }
 
                 /* set IFL2 flag */
diff --git a/core/mem68k.h b/core/mem68k.h
index 4148ac9..2d325e9 100644
--- a/core/mem68k.h
+++ b/core/mem68k.h
@@ -3,7 +3,7 @@
  *  Main 68k bus handlers
  *
  *  Copyright (C) 1998-2003  Charles Mac Donald (original code)
- *  Copyright (C) 2007-2017  Eke-Eke (Genesis Plus GX)
+ *  Copyright (C) 2007-2019  Eke-Eke (Genesis Plus GX)
  *
  *  Redistribution and use of this code or any derivative works are permitted
  *  provided that the following conditions are met: