From 58accf068963e3dbf2d94a49256d334c3548e571 Mon Sep 17 00:00:00 2001
From: ekeeke <ekeeke31@gmail.com>
Date: Fri, 25 Feb 2022 15:29:18 +0100
Subject: [PATCH] [Core/CD] fixed Memory Mode, Timer and Font Color registers
 byte access at even address (verified on real hardware, cf. Krikzz's
 mcd-verificator)

---
 core/cd_hw/scd.c | 15 ++++++++++++---
 core/cd_hw/scd.h |  2 +-
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/core/cd_hw/scd.c b/core/cd_hw/scd.c
index edb728d..f2f8ef8 100644
--- a/core/cd_hw/scd.c
+++ b/core/cd_hw/scd.c
@@ -2,7 +2,7 @@
  *  Genesis Plus
  *  Mega CD / Sega CD hardware
  *
- *  Copyright (C) 2012-2021  Eke-Eke (Genesis Plus GX)
+ *  Copyright (C) 2012-2022  Eke-Eke (Genesis Plus GX)
  *
  *  Redistribution and use of this code or any derivative works are permitted
  *  provided that the following conditions are met:
@@ -798,6 +798,7 @@ static void scd_write_byte(unsigned int address, unsigned int data)
     }
 
     case 0x03: /* Memory Mode */
+    case 0x02: /* !LDS and !UDS are ignored (verified on real hardware, cf. Krikzz's mcd-verificator) */
     {
       s68k_poll_sync(1<<0x03);
 
@@ -952,8 +953,8 @@ static void scd_write_byte(unsigned int address, unsigned int data)
       return;
     }
 
-    case 0x0e:  /* SUB-CPU communication flags */
-    case 0x0f:  /* !LWR is ignored (Space Ace, Dragon's Lair) */
+    case 0x0f:  /* SUB-CPU communication flags */
+    case 0x0e:  /* !LDS and !UDS are ignored (verified on real hardware, cf. Krikzz's mcd-verificator, Space Ace, Dragon's Lair) */
     {
       s68k_poll_sync(1<<0x0f);
       scd.regs[0x0f>>1].byte.l = data;
@@ -961,6 +962,7 @@ static void scd_write_byte(unsigned int address, unsigned int data)
     }
 
     case 0x31: /* Timer */
+    case 0x30: /* !LDS and !UDS are ignored (verified on real hardware, cf. Krikzz's mcd-verificator) */
     {
       /* reload timer (one timer clock = 384 CPU cycles) */
       scd.timer = data * TIMERS_SCYCLES_RATIO;
@@ -992,6 +994,13 @@ static void scd_write_byte(unsigned int address, unsigned int data)
       return;
     }
 
+    case 0x4d: /* Font Color */
+    case 0x4c: /* !LDS and !UDS are ignored (verified on real hardware, cf. Krikzz's mcd-verificator) */
+    {
+       scd.regs[0x4c>>1].byte.l = data;
+       break;
+    }
+
     default:
     {
       /* SUB-CPU communication words */
diff --git a/core/cd_hw/scd.h b/core/cd_hw/scd.h
index 49b66b0..8fafb66 100644
--- a/core/cd_hw/scd.h
+++ b/core/cd_hw/scd.h
@@ -2,7 +2,7 @@
  *  Genesis Plus
  *  Mega CD / Sega CD hardware
  *
- *  Copyright (C) 2012-2021  Eke-Eke (Genesis Plus GX)
+ *  Copyright (C) 2012-2022  Eke-Eke (Genesis Plus GX)
  *
  *  Redistribution and use of this code or any derivative works are permitted
  *  provided that the following conditions are met: