[libretro] fixed available system RAM size for SG-1000 games with extra on-board RAM

core/cart_hw/sms_cart.c

@@ -2,7 +2,7 @@
  *  Genesis Plus
  *  SG-1000, Master System & Game Gear cartridge hardware support
  *
- *  Copyright (C) 2007-2022  Eke-Eke (Genesis Plus GX)
+ *  Copyright (C) 2007-2023  Eke-Eke (Genesis Plus GX)
  *
  *  Redistribution and use of this code or any derivative works are permitted
  *  provided that the following conditions are met:
@@ -737,6 +737,24 @@ void sms_cart_switch(uint8 mode)
   }
 }
 
+int sms_cart_ram_size(void)
+{
+  if ((cart_rom.mapper == MAPPER_RAM_8K) || (cart_rom.mapper == MAPPER_RAM_8K_EXT1))
+  {
+    /* 8KB on-board RAM */
+    return 0x2000;
+  }
+
+  if (cart_rom.mapper == MAPPER_RAM_2K)
+  {
+    /* 2KB on-board RAM */
+    return 0x800;
+  }
+
+  /* no on-board RAM by default  */
+  return 0;
+}
+
 int sms_cart_region_detect(void)
 {
   int i = sizeof(game_list) / sizeof(rominfo_t) - 1;

core/cart_hw/sms_cart.h

@@ -2,7 +2,7 @@
  *  Genesis Plus
  *  SG-1000, Master System & Game Gear cartridge hardware support
  *
- *  Copyright (C) 2007-2022  Eke-Eke (Genesis Plus GX)
+ *  Copyright (C) 2007-2023  Eke-Eke (Genesis Plus GX)
  *
  *  Redistribution and use of this code or any derivative works are permitted
  *  provided that the following conditions are met:
@@ -47,6 +47,7 @@
 extern void sms_cart_init(void);
 extern void sms_cart_reset(void);
 extern void sms_cart_switch(uint8 mode);
+extern int sms_cart_ram_size(void);
 extern int sms_cart_region_detect(void);
 extern int sms_cart_context_save(uint8 *state);
 extern int sms_cart_context_load(uint8 *state);

libretro/libretro.c

@@ -3402,39 +3402,46 @@ size_t retro_get_memory_size(unsigned id)
    {
       case RETRO_MEMORY_SAVE_RAM:
       {
-        if (!sram.on)
+         /* return 0 if SRAM is disabled */
-          return 0;
+         if (!sram.on)
+            return 0;
 
-        /* if emulation is not running, we assume the frontend is requesting SRAM size for loading */
+         /* if emulation is not running, we assume the frontend is requesting SRAM size for loading so max supported size is returned */
-        if (!is_running)
+         if (!is_running)
-        {
-          /* max supported size is returned */
-          return 0x10000;
-        }
-
-        /* otherwise, we assume this is for saving and we need to check if SRAM data has been modified */
-        /* this is obviously not %100 safe since the frontend could still be trying to load SRAM while emulation is running */
-        /* a better solution would be that the frontend itself checks if data has been modified before writing it to a file */
-        for (i=0xffff; i>=0; i--)
-        {
-          if (sram.sram[i] != 0xff)
-          {
-            /* only save modified size */
-            return (i+1);
-          }
-        }
-      }
-      case RETRO_MEMORY_SYSTEM_RAM:
-         if (system_hw == SYSTEM_SG)
-            return 0x00400;
-         else if (system_hw == SYSTEM_SGII)
-            return 0x00800;
-         else if (system_hw == SYSTEM_SGII_RAM_EXT || system_hw == SYSTEM_SMS || system_hw == SYSTEM_SMS2 || system_hw == SYSTEM_GG || system_hw == SYSTEM_GGMS || system_hw == SYSTEM_PBC)
-            return 0x02000;
-         else
             return 0x10000;
-      default:
+
+         /* otherwise, we assume this is for saving and we return the size of SRAM data that has actually been modified */
+         /* this is obviously not %100 safe since the frontend could still be trying to load SRAM while emulation is running */
+         /* a better solution would be that the frontend itself checks if data has been modified before writing it to a file */
+         for (i=0xffff; i>=0; i--)
+            if (sram.sram[i] != 0xff)
+               return (i+1);
+
+         /* return 0 if SRAM is not modified */
          return 0;
+      }
+
+      case RETRO_MEMORY_SYSTEM_RAM:
+      {
+         /* 16-bit hardware */
+         if ((system_hw & SYSTEM_PBC) == SYSTEM_MD)
+            return 0x10000; /* 64KB internal RAM */
+
+         /* get 8-bit cartrige on-board RAM size */
+         i = sms_cart_ram_size();
+
+         if (i > 0)
+            return i + 0x2000; /* on-board RAM size + max 8KB internal RAM */
+         else if (system_hw == SYSTEM_SGII)
+            return 0x0800; /* 2KB internal RAM */
+         else if (system_hw == SYSTEM_SG)
+            return 0x0400; /* 1KB internal RAM */
+         else
+            return 0x2000; /* 8KB internal RAM */
+      }
+
+      default:
+        return 0;
    }
 }