From 0332db8961ef1b11b4f9e0326d3683b8e5d17730 Mon Sep 17 00:00:00 2001
From: Vicki Pfau <vi@endrift.com>
Date: Wed, 5 Dec 2018 19:39:29 -0800
Subject: [PATCH] GB Memory: Support running from blocked memory

---
 CHANGES         |  1 +
 src/gb/memory.c | 11 +++++++++++
 2 files changed, 12 insertions(+)

diff --git a/CHANGES b/CHANGES
index 1753ee27a..d9fc51a9f 100644
--- a/CHANGES
+++ b/CHANGES
@@ -6,6 +6,7 @@ Bugfixes:
 Misc:
  - GBA Savedata: EEPROM performance fixes
  - GBA Savedata: Automatically map 1Mbit Flash files as 1Mbit Flash
+ - GB Memory: Support running from blocked memory
 
 0.7.0: (Future)
 Features:
diff --git a/src/gb/memory.c b/src/gb/memory.c
index b2e229c4d..15ef917ad 100644
--- a/src/gb/memory.c
+++ b/src/gb/memory.c
@@ -45,6 +45,8 @@ static const enum GBBus _oamBlockCGB[] = {
 	GB_BUS_CPU // 0xE000
 };
 
+static const uint8_t _blockedRegion[1] = { 0xFF };
+
 static void _pristineCow(struct GB* gba);
 
 static uint8_t GBFastLoad8(struct LR35902Core* cpu, uint16_t address) {
@@ -92,6 +94,15 @@ static void GBSetActiveRegion(struct LR35902Core* cpu, uint16_t address) {
 		cpu->memory.cpuLoad8 = GBLoad8;
 		break;
 	}
+	if (gb->memory.dmaRemaining) {
+		const enum GBBus* block = gb->model < GB_MODEL_CGB ? _oamBlockDMG : _oamBlockCGB;
+		enum GBBus dmaBus = block[memory->dmaSource >> 13];
+		enum GBBus accessBus = block[address >> 13];
+		if ((dmaBus != GB_BUS_CPU && dmaBus == accessBus) || (address >= GB_BASE_OAM && address < GB_BASE_UNUSABLE)) {
+			cpu->memory.activeRegion = _blockedRegion;
+			cpu->memory.activeMask = 0;
+		}
+	}
 }
 
 static void _GBMemoryDMAService(struct mTiming* timing, void* context, uint32_t cyclesLate);