From 0e29be87355966dcc432fc0c6d3740d73bb8167d Mon Sep 17 00:00:00 2001
From: Fabrice de Gans <steelskin@gmail.com>
Date: Thu, 13 Apr 2023 14:14:06 -0700
Subject: [PATCH] Support multiple RAM sizes for MBC7

We rely on the rom size in the cartridge header as a proxy for the RAM
size. Only 3 cartridges exist that use MBC7, Korokoro Kirby / Kirby
Tilt'n'Rumble and Command Master. Both versions of Kirby use a 256 bytes
EEPROM while Command Master uses a 512 bytes EEPROM. There does not seem
to be any other way to reliably get the EEPROM size for MBC7 cartridges.
---
 src/gb/GB.cpp         | 16 +++-------------
 src/gb/gbCartData.cpp | 14 +++++++++++---
 2 files changed, 14 insertions(+), 16 deletions(-)

diff --git a/src/gb/GB.cpp b/src/gb/GB.cpp
index 734b4110..1d100944 100644
--- a/src/gb/GB.cpp
+++ b/src/gb/GB.cpp
@@ -58,10 +58,6 @@ 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;
@@ -472,17 +468,12 @@ bool gbInitializeRom(size_t romSize) {
                                         HUC3_RTC_DATA_SIZE, -4,
                                         &ResetHuc3RTC});
                 break;
-            case gbCartData::MapperType::kMbc7:
-                // For MBC7, we don't save the RAM data from the same location.
-                // TODO: Unify handling and find how to get the MBC7 RAM size.
-                g_vbamIoVecs.clear();
-                g_vbamIoVecs.push_back({&gbMemory[0xa000], kMbc7RamSizeForSaving});
-                break;
             case gbCartData::MapperType::kNone:
             case gbCartData::MapperType::kMbc1:
             case gbCartData::MapperType::kMbc2:
             case gbCartData::MapperType::kMbc5:
             case gbCartData::MapperType::kMbc6:
+            case gbCartData::MapperType::kMbc7:
             case gbCartData::MapperType::kHuC1:
             case gbCartData::MapperType::kMmm01:
             case gbCartData::MapperType::kPocketCamera:
@@ -3181,13 +3172,12 @@ bool gbReadGSASnapshot(const char* fileName)
             case gbCartData::MapperType::kMbc1:
             case gbCartData::MapperType::kMbc3:
             case gbCartData::MapperType::kMbc5:
+            case gbCartData::MapperType::kMbc7:
             case gbCartData::MapperType::kHuC1:
                 FREAD_UNCHECKED(gbRam, 1, g_gbCartData.ram_size(), file);
                 break;
             case gbCartData::MapperType::kMbc2:
-            case gbCartData::MapperType::kMbc7:
-                // TODO: Figure out how to get the RAM size for MBC7.
-                FREAD_UNCHECKED(&gbMemory[0xa000], 1, kMbc7RamSizeForSaving, file);
+                FREAD_UNCHECKED(&gbMemory[0xa000], 1, k256B, file);
                 break;
             default:
                 systemMessage(MSG_UNSUPPORTED_SNAPSHOT_FILE,
diff --git a/src/gb/gbCartData.cpp b/src/gb/gbCartData.cpp
index bf44c4cf..8253b552 100644
--- a/src/gb/gbCartData.cpp
+++ b/src/gb/gbCartData.cpp
@@ -356,10 +356,18 @@ 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_ = k512B;
+            if (header->rom_size == 0x05) {
+                // Kirby Tilt 'n' Tumble / Korokoro Kirby.
+                ram_size_ = k256B;
+            } else if (header->rom_size == 0x06) {
+                // Command Master.
+                ram_size_ = k512B;
+            } else {
+                // Not a licensed MBC7 cart. Default to the larger size and hope
+                // for the best.
+                ram_size_ = k512B;
+            }
             skip_ram = true;
             has_battery_ = true;
             has_rumble_ = true;