From ba11b8aa0cd8dca77efcd12913bbbfa74f69b04d Mon Sep 17 00:00:00 2001
From: Vicki Pfau <vi@endrift.com>
Date: Wed, 13 May 2020 20:11:10 -0700
Subject: [PATCH] GB MBC: Support 4MB MBC30 ROMs (fixes #1713)

---
 CHANGES      | 1 +
 src/gb/mbc.c | 5 ++++-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/CHANGES b/CHANGES
index 70f9592fa..512bbfdce 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,5 +1,6 @@
 0.8.2: (Future)
  - GB: Fix GBC game registers after skipping BIOS
+ - GB MBC: Support 4MB MBC30 ROMs (fixes mgba.io/i/1713)
  - GB Video: Fix BGPS value after skipping BIOS (fixes mgba.io/i/1717)
  - GBA: Add missing RTC overrides for Legendz games
  - GBA SIO: Fix Multiplayer busy bit
diff --git a/src/gb/mbc.c b/src/gb/mbc.c
index 6efe8b64d..be03f1511 100644
--- a/src/gb/mbc.c
+++ b/src/gb/mbc.c
@@ -518,7 +518,7 @@ static uint8_t _GBMBC2Read(struct GBMemory* memory, uint16_t address) {
 
 void _GBMBC3(struct GB* gb, uint16_t address, uint8_t value) {
 	struct GBMemory* memory = &gb->memory;
-	int bank = value & 0x7F;
+	int bank = value;
 	switch (address >> 13) {
 	case 0x0:
 		switch (value) {
@@ -536,6 +536,9 @@ void _GBMBC3(struct GB* gb, uint16_t address, uint8_t value) {
 		}
 		break;
 	case 0x1:
+		if (gb->memory.romSize < GB_SIZE_CART_BANK0 * 0x80) {
+			bank &= 0x7F;
+		}
 		if (!bank) {
 			++bank;
 		}