From 4a2bec239a4c661dff81c45f23a9be0144aed491 Mon Sep 17 00:00:00 2001
From: Lior Halphon <LIJI32@gmail.com>
Date: Fri, 30 Sep 2016 23:34:06 +0300
Subject: [PATCH] MBC2 RAM support was completely broken.

---
 Cocoa/Document.m |  2 +-
 Core/mbc.c       | 11 +++++++++--
 Core/memory.c    | 13 ++++++-------
 3 files changed, 16 insertions(+), 10 deletions(-)

diff --git a/Cocoa/Document.m b/Cocoa/Document.m
index aca44d2..15fc1aa 100644
--- a/Cocoa/Document.m
+++ b/Cocoa/Document.m
@@ -624,7 +624,7 @@ static uint32_t rgbEncode(GB_gameboy_t *gb, uint8_t r, uint8_t g, uint8_t b)
                 n_banks = gb.is_cgb ? 2 : 1;
                 break;
             case GBMemoryExternalRAM:
-                n_banks = gb.mbc_ram_size / 0x2000;
+                n_banks = (gb.mbc_ram_size + 0x1FFF) / 0x2000;
                 break;
             case GBMemoryRAM:
                 n_banks = gb.is_cgb ? 8 : 1;
diff --git a/Core/mbc.c b/Core/mbc.c
index 2719208..80fde6e 100644
--- a/Core/mbc.c
+++ b/Core/mbc.c
@@ -106,9 +106,16 @@ void GB_configure_cart(GB_gameboy_t *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]];
+        if (gb->cartridge_type->mbc_type == GB_MBC2) {
+            gb->mbc_ram_size = 0x200;
+        }
+        else {
+            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);
+
+        /* Todo: Some games assume unintialized MBC RAM is 0xFF. It this true for all cartridges types?*/
         memset(gb->mbc_ram, 0xFF, gb->mbc_ram_size);
     }
 
diff --git a/Core/memory.c b/Core/memory.c
index 9517081..819e4d0 100644
--- a/Core/memory.c
+++ b/Core/memory.c
@@ -86,7 +86,11 @@ static uint8_t read_mbc_ram(GB_gameboy_t *gb, uint16_t addr)
         return 0xFF;
     }
 
-    return gb->mbc_ram[((addr & 0x1FFF) + gb->mbc_ram_bank * 0x2000) & (gb->mbc_ram_size - 1)];
+    uint8_t ret = gb->mbc_ram[((addr & 0x1FFF) + gb->mbc_ram_bank * 0x2000) & (gb->mbc_ram_size - 1)];
+    if (gb->cartridge_type->mbc_type == GB_MBC2) {
+        ret |= 0xF0;
+    }
+    return ret;
 }
 
 static uint8_t read_ram(GB_gameboy_t *gb, uint16_t addr)
@@ -278,8 +282,7 @@ static void write_mbc(GB_gameboy_t *gb, uint16_t addr, uint8_t value)
             break;
         case GB_MBC2:
             switch (addr & 0xF000) {
-                /* Todo: is this correct? */
-                case 0x0000: case 0x1000: if (!(addr & 0x100)) gb->mbc_ram_enable = value & 0x1; break;
+                case 0x0000: case 0x1000: if (!(addr & 0x100)) gb->mbc_ram_enable = value == 10; break;
                 case 0x2000: case 0x3000: if (  addr & 0x100)  gb->mbc2.rom_bank  = value; break;
             }
             break;
@@ -326,10 +329,6 @@ static void write_mbc_ram(GB_gameboy_t *gb, uint16_t addr, uint8_t value)
         gb->rtc_latched.data[gb->mbc_ram_bank - 8] = gb->rtc_real.data[gb->mbc_ram_bank - 8] = value; /* Todo: does it really write both? */
     }
 
-    if (gb->cartridge_type->mbc_type == GB_MBC2) {
-        value &= 0xF;
-    }
-
     if (!gb->mbc_ram) {
         return;
     }