From 4a41ee1525eb11a5d06511c2c38248d0e34aba3e Mon Sep 17 00:00:00 2001
From: EkeEke <ekeeke31@gmail.com>
Date: Mon, 22 Oct 2012 16:01:03 +0200
Subject: [PATCH] improved MAIN-SUB memory map mirroring in SCD mode (verified
 on real hardware by Charles McDonald)

---
 source/cd_hw/scd.c | 16 ++--------------
 source/mem68k.c    | 40 ++++++++++++++++++++++++----------------
 2 files changed, 26 insertions(+), 30 deletions(-)

diff --git a/source/cd_hw/scd.c b/source/cd_hw/scd.c
index bc75284..e10a0b1 100644
--- a/source/cd_hw/scd.c
+++ b/source/cd_hw/scd.c
@@ -1045,7 +1045,7 @@ void scd_init(void)
   {
     if (i & 2)
     {
-      /* PRG-RAM (first 128KB bank, mirrored ?) */
+      /* PRG-RAM (first 128KB bank, mirrored) */
       m68k.memory_map[i].base    = scd.prg_ram + ((i & 1) << 16);
       m68k.memory_map[i].read8   = NULL;
       m68k.memory_map[i].read16  = NULL;
@@ -1068,7 +1068,7 @@ void scd_init(void)
     }
   }
 
-  /* $200000-$23FFFF (resp. $600000-$63FFFF): Word-RAM in 2M mode (256KB) */
+  /* $200000-$3FFFFF (resp. $600000-$7FFFFF): Word-RAM in 2M mode (256KB mirrored) */
   for (i=base+0x20; i<base+0x24; i++)
   {
     m68k.memory_map[i].base    = scd.word_ram_2M + ((i & 3) << 16);
@@ -1079,18 +1079,6 @@ void scd_init(void)
     zbank_memory_map[i].read   = NULL;
     zbank_memory_map[i].write  = NULL;
   }
-
-  /* $240000-$3FFFFF (resp. $400000-$7FFFFF): unused area (Word-RAM mirrored ?) */
-  for (i=base+0x24; i<base+0x40; i++)
-  {
-    m68k.memory_map[i].base     = scd.word_ram_2M + ((i & 3) << 16);
-    m68k.memory_map[i].read8    = m68k_read_bus_8;
-    m68k.memory_map[i].read16   = m68k_read_bus_16;
-    m68k.memory_map[i].write8   = m68k_unused_8_w;
-    m68k.memory_map[i].write16  = m68k_unused_16_w;
-    zbank_memory_map[i].read    = zbank_unused_r;
-    zbank_memory_map[i].write   = zbank_unused_w;
-  }
   
   /****************************************************************/
   /*  SUB-CPU memory map ($000000-$FFFFFF)                        */
diff --git a/source/mem68k.c b/source/mem68k.c
index 5e0f370..c970e0e 100644
--- a/source/mem68k.c
+++ b/source/mem68k.c
@@ -322,37 +322,40 @@ unsigned int ctrl_io_read_byte(unsigned int address)
 #endif
       if (system_hw == SYSTEM_MCD)
       {
+        /* register index ($A12000-A1203F mirrored up to $A120FF) */
+        uint8 index = address & 0x3f;
+
         /* Memory Mode */
-        if (address == 0xa12003)
+        if (index == 0x03)
         {
           m68k_poll_detect(0x03);
           return scd.regs[0x03>>1].byte.l;
         }
 
         /* SUB-CPU communication flags */
-        if (address == 0xa1200f)
+        if (index == 0x0f)
         {
           m68k_poll_detect(0x0f);
           return scd.regs[0x0f>>1].byte.l;
         }
 
         /* default registers */
-        if (address < 0xa12030)
+        if (index < 0x30)
         {
           /* SUB-CPU communication words */
-          if (address >= 0xa12020)
+          if (index >= 0x20)
           {
-            m68k_poll_detect((address - 0x10) & 0x1f);
+            m68k_poll_detect(index - 0x10);
           }
 
           /* register LSB */
           if (address & 1)
           {
-            return scd.regs[(address >> 1) & 0xff].byte.l;
+            return scd.regs[index >> 1].byte.l;
           }
               
           /* register MSB */
-          return scd.regs[(address >> 1) & 0xff].byte.h;
+          return scd.regs[index >> 1].byte.h;
         }
       }
 
@@ -441,35 +444,38 @@ unsigned int ctrl_io_read_word(unsigned int address)
 #endif
       if (system_hw == SYSTEM_MCD)
       {
+        /* register index ($A12000-A1203F mirrored up to $A120FF) */
+        uint8 index = address & 0x3f;
+
         /* Memory Mode */
-        if (address == 0xa12002)
+        if (index == 0x02)
         {
           m68k_poll_detect(0x03);
           return scd.regs[0x03>>1].w;
         }
 
         /* CDC host data (word access only ?) */
-        if (address == 0xa12008)
+        if (index == 0x08)
         {
           return cdc_host_r();
         }
 
         /* H-INT vector (word access only ?) */
-        if (address == 0xa12006)
+        if (index == 0x06)
         {
           return *(uint16 *)(m68k.memory_map[0].base + 0x72);
         }
 
         /* default registers */
-        if (address < 0xa12030)
+        if (index < 0x30)
         {
           /* SUB-CPU communication words */
-          if (address >= 0xa12020)
+          if (index >= 0x20)
           {
-            m68k_poll_detect((address - 0x10) & 0x1e);
+            m68k_poll_detect(index - 0x10);
           }
           
-          return scd.regs[(address >> 1) & 0xff].w;
+          return scd.regs[index >> 1].w;
         }
       }
 
@@ -565,7 +571,8 @@ void ctrl_io_write_byte(unsigned int address, unsigned int data)
 #endif
       if (system_hw == SYSTEM_MCD)
       {
-        switch (address & 0xff)
+        /* register index ($A12000-A1203F mirrored up to $A120FF) */
+        switch (address & 0x3f)
         {
           case 0x00:  /* SUB-CPU interrupt */
           {
@@ -795,7 +802,8 @@ void ctrl_io_write_word(unsigned int address, unsigned int data)
 #endif
       if (system_hw == SYSTEM_MCD)
       {
-        switch (address & 0xfe)
+        /* register index ($A12000-A1203F mirrored up to $A120FF) */
+        switch (address & 0x3e)
         {
           case 0x00:  /* SUB-CPU interrupt & control */
           {