From d0aa36acc3179b5db6c38a8aa460d91bb17c7ad6 Mon Sep 17 00:00:00 2001
From: EkeEke <ekeeke31@gmail.com>
Date: Sun, 7 Jan 2018 16:24:28 +0100
Subject: [PATCH] [Core/CPU] improved 68K/Z80 synchronization

---
 core/genesis.c | 10 +++++-----
 core/genesis.h |  2 +-
 core/system.c  | 42 +-----------------------------------------
 core/system.h  |  2 +-
 4 files changed, 8 insertions(+), 48 deletions(-)

diff --git a/core/genesis.c b/core/genesis.c
index 1ef2db9..1d5d272 100644
--- a/core/genesis.c
+++ b/core/genesis.c
@@ -5,7 +5,7 @@
  *  Support for SG-1000, Mark-III, Master System, Game Gear, Mega Drive & Mega CD hardware
  *
  *  Copyright (C) 1998-2003  Charles Mac Donald (original code)
- *  Copyright (C) 2007-2016  Eke-Eke (Genesis Plus GX)
+ *  Copyright (C) 2007-2018  Eke-Eke (Genesis Plus GX)
  *
  *  Redistribution and use of this code or any derivative works are permitted
  *  provided that the following conditions are met:
@@ -474,8 +474,8 @@ void gen_zbusreq_w(unsigned int data, unsigned int cycles)
     /* check if Z80 is going to be restarted */
     if (zstate == 3)
     {
-      /* resynchronize with 68k */
-      Z80.cycles = cycles;
+      /* resynchronize with 68k (Z80 cycles should remain a multiple of 15 MClocks) */
+      Z80.cycles = ((cycles + 14) / 15) * 15;
 
       /* disable 68k access to Z80 bus */
       m68k.memory_map[0xa0].read8   = m68k_read_bus_8;
@@ -496,8 +496,8 @@ void gen_zreset_w(unsigned int data, unsigned int cycles)
     /* check if Z80 is going to be restarted */
     if (zstate == 0)
     {
-      /* resynchronize with 68k */
-      Z80.cycles = cycles;
+      /* resynchronize with 68k (Z80 cycles should remain a multiple of 15 MClocks) */
+      Z80.cycles = ((cycles + 14) / 15) * 15;
 
       /* reset Z80 & YM2612 */
       z80_reset();
diff --git a/core/genesis.h b/core/genesis.h
index 15fd52f..8a744db 100644
--- a/core/genesis.h
+++ b/core/genesis.h
@@ -5,7 +5,7 @@
  *  Support for SG-1000, Mark-III, Master System, Game Gear, Mega Drive & Mega CD hardware
  *
  *  Copyright (C) 1998-2003  Charles Mac Donald (original code)
- *  Copyright (C) 2007-2016  Eke-Eke (Genesis Plus GX)
+ *  Copyright (C) 2007-2018  Eke-Eke (Genesis Plus GX)
  *
  *  Redistribution and use of this code or any derivative works are permitted
  *  provided that the following conditions are met:
diff --git a/core/system.c b/core/system.c
index ead4c5d..358262e 100644
--- a/core/system.c
+++ b/core/system.c
@@ -5,7 +5,7 @@
  *  Support for 16-bit & 8-bit hardware modes
  *
  *  Copyright (C) 1998-2003  Charles Mac Donald (original code)
- *  Copyright (C) 2007-2017  Eke-Eke (Genesis Plus GX)
+ *  Copyright (C) 2007-2018  Eke-Eke (Genesis Plus GX)
  *
  *  Redistribution and use of this code or any derivative works are permitted
  *  provided that the following conditions are met:
@@ -467,10 +467,6 @@ void system_frame_gen(int do_skip)
     {
       z80_run(788);
     }
-    else
-    {
-      Z80.cycles = 788;
-    }
 
     /* set VINT flag */
     status |= 0x80;    
@@ -493,10 +489,6 @@ void system_frame_gen(int do_skip)
   {
     z80_run(MCYCLES_PER_LINE);
   }
-  else
-  {
-    Z80.cycles = MCYCLES_PER_LINE;
-  }
 
   /* Z80 interrupt is cleared at the end of the line */
   Z80.irq_state = CLEAR_LINE;
@@ -538,10 +530,6 @@ void system_frame_gen(int do_skip)
     {
       z80_run(mcycles_vdp + MCYCLES_PER_LINE);
     }
-    else
-    {
-      Z80.cycles = mcycles_vdp + MCYCLES_PER_LINE;
-    }
 
     /* run SVP chip */
     if (svp)
@@ -590,10 +578,6 @@ void system_frame_gen(int do_skip)
   {
     z80_run(mcycles_vdp + MCYCLES_PER_LINE);
   }
-  else
-  {
-    Z80.cycles = mcycles_vdp + MCYCLES_PER_LINE;
-  }
 
   /* run SVP chip */
   if (svp)
@@ -654,10 +638,6 @@ void system_frame_gen(int do_skip)
     {
       z80_run(mcycles_vdp + MCYCLES_PER_LINE);
     }
-    else
-    {
-      Z80.cycles = mcycles_vdp + MCYCLES_PER_LINE;
-    }
 
     /* run SVP chip */
     if (svp)
@@ -826,10 +806,6 @@ void system_frame_scd(int do_skip)
     {
       z80_run(788);
     }
-    else
-    {
-      Z80.cycles = 788;
-    }
 
     /* set VINT flag */
     status |= 0x80;    
@@ -854,10 +830,6 @@ void system_frame_scd(int do_skip)
   {
     z80_run(MCYCLES_PER_LINE);
   }
-  else
-  {
-    Z80.cycles = MCYCLES_PER_LINE;
-  }
 
   /* Z80 interrupt is cleared at the end of the line */
   Z80.irq_state = CLEAR_LINE;
@@ -895,10 +867,6 @@ void system_frame_scd(int do_skip)
     {
       z80_run(mcycles_vdp + MCYCLES_PER_LINE);
     }
-    else
-    {
-      Z80.cycles = mcycles_vdp + MCYCLES_PER_LINE;
-    }
 
     /* update VDP cycle count */
     mcycles_vdp += MCYCLES_PER_LINE;
@@ -943,10 +911,6 @@ void system_frame_scd(int do_skip)
   {
     z80_run(mcycles_vdp + MCYCLES_PER_LINE);
   }
-  else
-  {
-    Z80.cycles = mcycles_vdp + MCYCLES_PER_LINE;
-  }
 
   /* update VDP cycle count */
   mcycles_vdp += MCYCLES_PER_LINE;
@@ -1003,10 +967,6 @@ void system_frame_scd(int do_skip)
     {
       z80_run(mcycles_vdp + MCYCLES_PER_LINE);
     }
-    else
-    {
-      Z80.cycles = mcycles_vdp + MCYCLES_PER_LINE;
-    }
 
     /* update VDP cycle count */
     mcycles_vdp += MCYCLES_PER_LINE;
diff --git a/core/system.h b/core/system.h
index a61d19b..ac72727 100644
--- a/core/system.h
+++ b/core/system.h
@@ -5,7 +5,7 @@
  *  Support for 16-bit & 8-bit hardware modes
  *
  *  Copyright (C) 1998-2003  Charles Mac Donald (original code)
- *  Copyright (C) 2007-2017  Eke-Eke (Genesis Plus GX)
+ *  Copyright (C) 2007-2018  Eke-Eke (Genesis Plus GX)
  *
  *  Redistribution and use of this code or any derivative works are permitted
  *  provided that the following conditions are met: