Support for an alternative MBC1 wiring, should solve most N-in-1 carts (Issue #3)

Core/debugger.c

@@ -854,9 +854,14 @@ static bool mbc(GB_gameboy_t *gb, char *arguments)
             GB_log(gb, "Current mapped RAM bank: %x\n", gb->mbc_ram_bank);
             GB_log(gb, "RAM is curently %s\n", gb->mbc_ram_enable? "enabled" : "disabled");
         }
-        if (cartridge->mbc_type == GB_MBC1) {
+        if (cartridge->mbc_type == GB_MBC1 && gb->mbc1_wiring == GB_STANDARD_MBC1_WIRING) {
             GB_log(gb, "MBC1 banking mode is %s\n", gb->mbc1.mode == 1 ? "RAM" : "ROM");
         }
+        if (cartridge->mbc_type == GB_MBC1 && gb->mbc1_wiring == GB_MBC1M_WIRING) {
+            GB_log(gb, "MBC1 uses MBC1M wiring. \n");
+            GB_log(gb, "Current mapped ROM0 bank: %x\n", gb->mbc_rom0_bank);
+            GB_log(gb, "MBC1 multicart banking mode is %s\n", gb->mbc1.mode == 1 ? "enabled" : "disabled");
+        }
 
     }
     else {

Core/gb.c

@@ -165,12 +165,7 @@ int GB_load_rom(GB_gameboy_t *gb, const char *path)
     memset(gb->rom, 0xFF, gb->rom_size); /* Pad with 0xFFs */
     fread(gb->rom, gb->rom_size, 1, f);
     fclose(f);
-    gb->cartridge_type = &GB_cart_defs[gb->rom[0x147]];
+    GB_configure_cart(gb);
-    if (gb->cartridge_type->has_ram) {
-        static const int ram_sizes[256] = {0, 0x800, 0x2000, 0x8000, 0x20000, 0x10000};
-        gb->mbc_ram_size = ram_sizes[gb->rom[0x149]];
-        gb->mbc_ram = malloc(gb->mbc_ram_size);
-    }
 
     return 0;
 }

Core/gb.h

@@ -312,6 +312,10 @@ typedef struct GB_gameboy_s {
     uint8_t *rom;
     uint32_t rom_size;
     const GB_cartridge_t *cartridge_type;
+    enum {
+        GB_STANDARD_MBC1_WIRING,
+        GB_MBC1M_WIRING,
+    } mbc1_wiring;
 
     /* Various RAMs */
     uint8_t *ram;

Core/mbc.c

@@ -1,4 +1,6 @@
 #include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
 #include "gb.h"
 
 const GB_cartridge_t GB_cart_defs[256] = {
@@ -50,14 +52,32 @@ void GB_update_mbc_mappings(GB_gameboy_t *gb)
     switch (gb->cartridge_type->mbc_type) {
         case GB_NO_MBC: case GB_MBC4: return;
         case GB_MBC1:
-            /* Standard MBC1 wiring: */
+            /* Todo: some obscure behaviors of MBC1 are not supported. See http://forums.nesdev.com/viewtopic.php?f=20&t=14099 */
             if (gb->mbc1.mode == 0) {
+                switch (gb->mbc1_wiring) {
+                    case GB_STANDARD_MBC1_WIRING:
                         gb->mbc_rom_bank = gb->mbc1.bank_low | (gb->mbc1.bank_high << 5);
                         gb->mbc_ram_bank = 0;
+                        break;
+
+                    case GB_MBC1M_WIRING:
+                        gb->mbc_rom_bank = (gb->mbc1.bank_low & 0xF) | (gb->mbc1.bank_high << 4);
+                        gb->mbc_ram_bank = 0;
+                        gb->mbc_rom0_bank = 0;
+                }
             }
             else {
+                switch (gb->mbc1_wiring) {
+                    case GB_STANDARD_MBC1_WIRING:
                         gb->mbc_rom_bank = gb->mbc1.bank_low;
                         gb->mbc_ram_bank = gb->mbc1.bank_high;
+                        break;
+                        
+                    case GB_MBC1M_WIRING:
+                        gb->mbc_rom_bank = (gb->mbc1.bank_low & 0xF) | (gb->mbc1.bank_high << 4);
+                        gb->mbc_rom0_bank = gb->mbc1.bank_high << 4;
+                        gb->mbc_ram_bank = 0;
+                }
             }
             break;
         case GB_MBC2:
@@ -76,3 +96,24 @@ void GB_update_mbc_mappings(GB_gameboy_t *gb)
         gb->mbc_rom_bank = 1;
     }
 }
+
+void GB_configure_cart(GB_gameboy_t *gb)
+{
+    gb->cartridge_type = &GB_cart_defs[gb->rom[0x147]];
+
+    if (gb->cartridge_type->has_ram) {
+        static const int ram_sizes[256] = {0, 0x800, 0x2000, 0x8000, 0x20000, 0x10000};
+        gb->mbc_ram_size = ram_sizes[gb->rom[0x149]];
+        gb->mbc_ram = malloc(gb->mbc_ram_size);
+    }
+
+    /* MBC1 has at least 3 types of wiring (We currently support two (Standard and 4bit-MBC1M) of these).
+       See http://forums.nesdev.com/viewtopic.php?f=20&t=14099 */
+
+    /* Attempt to "guess" wiring */
+    if (gb->cartridge_type->mbc_type == GB_MBC1) {
+        if (gb->rom_size >= 0x44000 && memcmp(gb->rom + 0x104, gb->rom + 0x40104, 0x30) == 0) {
+            gb->mbc1_wiring = GB_MBC1M_WIRING;
+        }
+    }
+}

Core/mbc.h

@@ -4,5 +4,5 @@
 
 extern const GB_cartridge_t GB_cart_defs[256];
 void GB_update_mbc_mappings(GB_gameboy_t *gb);
-
+void GB_configure_cart(GB_gameboy_t *gb);
 #endif /* MBC_h */