From 16589b558fd0ff16e39c4a1811209f1f345d0126 Mon Sep 17 00:00:00 2001
From: ekeeke <ekeeke31@gmail.com>
Date: Fri, 19 Jan 2024 00:01:02 +0100
Subject: [PATCH] [Core/CD] improved accuracy of CDC transfer to Main-CPU
 (resp. Sub-CPU) when destination is set to Sub-CPU (resp. Main-CPU) (verified
 on real hardware, cf. Krikzz's mcd-verificator)

---
 core/cd_hw/cdc.c | 8 ++++----
 core/cd_hw/cdc.h | 7 +++++--
 core/cd_hw/scd.c | 2 +-
 core/mem68k.c    | 2 +-
 4 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/core/cd_hw/cdc.c b/core/cd_hw/cdc.c
index 1679a16..db6efa6 100644
--- a/core/cd_hw/cdc.c
+++ b/core/cd_hw/cdc.c
@@ -2,7 +2,7 @@
  *  Genesis Plus
  *  CD data controller (LC8951x compatible)
  *
- *  Copyright (C) 2012-2023  Eke-Eke (Genesis Plus GX)
+ *  Copyright (C) 2012-2024  Eke-Eke (Genesis Plus GX)
  *
  *  Redistribution and use of this code or any derivative works are permitted
  *  provided that the following conditions are met:
@@ -769,13 +769,13 @@ unsigned char cdc_reg_r(void)
   return data;
 }
 
-unsigned short cdc_host_r(void)
+unsigned short cdc_host_r(uint8 cpu_access)
 {
   /* read CDC buffered data (gate-array register $08) */
   uint16 data = scd.regs[0x08>>1].w;
 
-  /* check if host data transfer is enabled */
-  if (scd.regs[0x04>>1].byte.h & 0x40)
+  /* check if host data transfer is started for selected CPU */
+  if ((scd.regs[0x04>>1].byte.h & 0x47) == cpu_access)
   {
     /* check if EDT bit (gate-array register $04) is set (host data transfer is finished) */
     if (scd.regs[0x04>>1].byte.h & 0x80)
diff --git a/core/cd_hw/cdc.h b/core/cd_hw/cdc.h
index fe85e6a..a33af9d 100644
--- a/core/cd_hw/cdc.h
+++ b/core/cd_hw/cdc.h
@@ -2,7 +2,7 @@
  *  Genesis Plus
  *  CD data controller (LC8951x compatible)
  *
- *  Copyright (C) 2012-2023  Eke-Eke (Genesis Plus GX)
+ *  Copyright (C) 2012-2024  Eke-Eke (Genesis Plus GX)
  *
  *  Redistribution and use of this code or any derivative works are permitted
  *  provided that the following conditions are met:
@@ -40,6 +40,9 @@
 
 #define cdc scd.cdc_hw
 
+#define CDC_MAIN_CPU_ACCESS 0x42
+#define CDC_SUB_CPU_ACCESS  0x43
+
 /* CDC hardware */
 typedef struct
 {
@@ -67,6 +70,6 @@ extern void cdc_dma_update(void);
 extern void cdc_decoder_update(uint32 header);
 extern void cdc_reg_w(unsigned char data);
 extern unsigned char cdc_reg_r(void);
-extern unsigned short cdc_host_r(void);
+extern unsigned short cdc_host_r(uint8 cpu_access);
 
 #endif
diff --git a/core/cd_hw/scd.c b/core/cd_hw/scd.c
index 76d0095..0fb03a8 100644
--- a/core/cd_hw/scd.c
+++ b/core/cd_hw/scd.c
@@ -680,7 +680,7 @@ static unsigned int scd_read_word(unsigned int address)
   /* CDC host data (word access only ?) */
   if (address == 0x08)
   {
-    return cdc_host_r();
+    return cdc_host_r(CDC_SUB_CPU_ACCESS);
   }
 
   /* LED & RESET status */
diff --git a/core/mem68k.c b/core/mem68k.c
index cae39b0..43f9bb7 100644
--- a/core/mem68k.c
+++ b/core/mem68k.c
@@ -537,7 +537,7 @@ unsigned int ctrl_io_read_word(unsigned int address)
           {
             s68k_sync();
           }
-          return cdc_host_r();
+          return cdc_host_r(CDC_MAIN_CPU_ACCESS);
         }
 
         /* H-INT vector (word access only ?) */