From 75b79d91f19591f6c9914dafff85a0b86adc8850 Mon Sep 17 00:00:00 2001
From: Fabrice de Gans <steelskin@gmail.com>
Date: Fri, 7 Apr 2023 13:27:31 -0700
Subject: [PATCH] Change MBC7 reported RAM size to 512 bytes

Some MBC7 cartridges use 512 bytes EEPROM rather than 256 bytes. For
compatibility with older versions, we keep saving and loading 256 bytes
of EEPROM for every MBC7 cartridge. TODOs have been left to figure out
how to identify the EEPROM capacity properly.
---
 src/gb/GB.cpp         | 21 +++++++++++----------
 src/gb/gbCartData.cpp |  4 +++-
 2 files changed, 14 insertions(+), 11 deletions(-)

diff --git a/src/gb/GB.cpp b/src/gb/GB.cpp
index 5071b676..734b4110 100644
--- a/src/gb/GB.cpp
+++ b/src/gb/GB.cpp
@@ -58,6 +58,10 @@ struct VBamIoVec {
 };
 std::vector<VBamIoVec> g_vbamIoVecs;
 
+// TODO: This is set to 256 bytes for compatibility with older versions. We
+// should figure out how to actually get the MBC7 RAM size.
+static constexpr size_t kMbc7RamSizeForSaving = k256B;
+
 void ResetMBC3RTC() {
     time(&gbDataMBC3.mapperLastTime);
     struct tm* lt;
@@ -470,10 +474,9 @@ bool gbInitializeRom(size_t romSize) {
                 break;
             case gbCartData::MapperType::kMbc7:
                 // For MBC7, we don't save the RAM data from the same location.
-                // TODO: Unify handling.
+                // TODO: Unify handling and find how to get the MBC7 RAM size.
                 g_vbamIoVecs.clear();
-                g_vbamIoVecs.push_back({&gbMemory[0xa000],
-                                        g_gbCartData.ram_size()});
+                g_vbamIoVecs.push_back({&gbMemory[0xa000], kMbc7RamSizeForSaving});
                 break;
             case gbCartData::MapperType::kNone:
             case gbCartData::MapperType::kMbc1:
@@ -3183,7 +3186,8 @@ bool gbReadGSASnapshot(const char* fileName)
                 break;
             case gbCartData::MapperType::kMbc2:
             case gbCartData::MapperType::kMbc7:
-                FREAD_UNCHECKED(&gbMemory[0xa000], 1, 256, file);
+                // TODO: Figure out how to get the RAM size for MBC7.
+                FREAD_UNCHECKED(&gbMemory[0xa000], 1, kMbc7RamSizeForSaving, file);
                 break;
             default:
                 systemMessage(MSG_UNSUPPORTED_SNAPSHOT_FILE,
@@ -4951,12 +4955,9 @@ bool gbApplyPatch(const char* patchName) {
         return false;
     }
 
-    size_t newSize = size;
-    if (newSize != g_gbCartData.rom_size()) {
-        return gbInitializeRom(newSize);
-    }
-
-    return true;
+    // We should re-parse the header every time in case a patch has changed the
+    // ROM header.
+    return gbInitializeRom(size);
 }
 #endif  // __LIBRETRO__
 
diff --git a/src/gb/gbCartData.cpp b/src/gb/gbCartData.cpp
index 6b247877..bf44c4cf 100644
--- a/src/gb/gbCartData.cpp
+++ b/src/gb/gbCartData.cpp
@@ -356,8 +356,10 @@ gbCartData::gbCartData(const uint8_t* romData, size_t romDataSize) {
             break;
         case 0x22:
             // MBC7 header does not specify a RAM size so set it here.
+            // TODO: Figure out how to get the RAM size for MBC7. It is either
+            // 256 or 512 Bytes.
             mapper_type_ = MapperType::kMbc7;
-            ram_size_ = k256B;
+            ram_size_ = k512B;
             skip_ram = true;
             has_battery_ = true;
             has_rumble_ = true;