From 773e0d26ffd5e15c99d50bc6e5cb66fe167d85f4 Mon Sep 17 00:00:00 2001
From: Vicki Pfau <vi@endrift.com>
Date: Sat, 6 Jul 2019 16:13:39 -0700
Subject: [PATCH] GB Memory: Better emulate 0xFEA0 region on DMG, MGB and AGB

---
 CHANGES         |  1 +
 src/gb/memory.c | 13 ++++++++++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/CHANGES b/CHANGES
index a8304684e..b0e021ceb 100644
--- a/CHANGES
+++ b/CHANGES
@@ -34,6 +34,7 @@ Emulation fixes:
  - GB Audio: Deschedule channel 1 when disabled by sweep (fixes mgba.io/i/1467)
  - GBA Memory: Fix STM/LDM to invalid VRAM
  - GB: Fix savedata initialization (fixes mgba.io/i/1473, mgba.io/i/1478)
+ - GB Memory: Better emulate 0xFEA0 region on DMG, MGB and AGB
 Other fixes:
  - Qt: Fix some Qt display driver race conditions
  - Core: Improved lockstep driver reliability (Le Hoang Quyen)
diff --git a/src/gb/memory.c b/src/gb/memory.c
index 15ef917ad..b3b9b8bcf 100644
--- a/src/gb/memory.c
+++ b/src/gb/memory.c
@@ -234,7 +234,7 @@ uint8_t GBLoad8(struct LR35902Core* cpu, uint16_t address) {
 		if (dmaBus != GB_BUS_CPU && dmaBus == accessBus) {
 			return 0xFF;
 		}
-		if (address >= GB_BASE_OAM && address < GB_BASE_UNUSABLE) {
+		if (address >= GB_BASE_OAM && address < GB_BASE_IO) {
 			return 0xFF;
 		}
 	}
@@ -471,6 +471,17 @@ uint8_t GBView8(struct LR35902Core* cpu, uint16_t address, int segment) {
 		}
 		if (address < GB_BASE_IO) {
 			mLOG(GB_MEM, GAME_ERROR, "Attempt to read from unusable memory: %04X", address);
+			if (gb->video.mode < 2) {
+				switch (gb->model) {
+				case GB_MODEL_AGB:
+					return (address & 0xF0) | ((address >> 4) & 0xF);
+				case GB_MODEL_CGB:
+					// TODO: R/W behavior
+					return 0x00;
+				default:
+					return 0x00;
+				}
+			}
 			return 0xFF;
 		}
 		if (address < GB_BASE_HRAM) {