@@ -1,4 +1,6 @@
 0.6.0: (Future)
+Features:
+ - GBA: Support printing debug strings from inside a game
 Bugfixes:
  - GB MBC: Fix MBC7 when size is incorrectly specified
  - GB Video: Setting LYC=LY during mode 2 should trigger an IRQ

@@ -27,6 +27,7 @@ #include "util/patch.h"
 #include "util/vfs.h"
 
 mLOG_DEFINE_CATEGORY(GBA, "GBA");
+mLOG_DEFINE_CATEGORY(GBA_DEBUG, "GBA Debug");
 
 const uint32_t GBA_COMPONENT_MAGIC = 0x1000000;
 
@@ -199,6 +200,9 @@ gba->lastJump = 0;
 	gba->haltPending = false;
 	gba->idleDetectionStep = 0;
 	gba->idleDetectionFailures = 0;
+
+	gba->debug = false;
+	memset(gba->debugString, 0, sizeof(gba->debugString));
 }
 
 void GBASkipBIOS(struct GBA* gba) {
@@ -679,6 +683,19 @@ return;
 	}
 	gba->cpu->nextEvent = gba->cpu->cycles;
 	gba->stopCallback->stop(gba->stopCallback);
+}
+
+void GBADebug(struct GBA* gba, uint16_t flags) {
+	gba->debugFlags = flags;
+	if (GBADebugFlagsIsSend(gba->debugFlags)) {
+		int level = 1 << GBADebugFlagsGetLevel(gba->debugFlags);
+		level &= 0x1F;
+		char oolBuf[0x101];
+		strncpy(oolBuf, gba->debugString, sizeof(gba->debugString));
+		oolBuf[0x100] = '\0';
+		mLog(_mLOG_CAT_GBA_DEBUG(), level, "%s", oolBuf);
+	}
+	gba->debugFlags = GBADebugFlagsClearSend(gba->debugFlags);
 }
 
 bool GBAIsROM(struct VFile* vf) {

@@ -53,12 +53,17 @@ struct Patch;
 struct VFile;
 
 mLOG_DECLARE_CATEGORY(GBA);
+mLOG_DECLARE_CATEGORY(GBA_DEBUG);
 
 DECL_BITFIELD(GBATimerFlags, uint32_t);
 DECL_BITS(GBATimerFlags, PrescaleBits, 0, 4);
 DECL_BIT(GBATimerFlags, CountUp, 4);
 DECL_BIT(GBATimerFlags, DoIrq, 5);
 DECL_BIT(GBATimerFlags, Enable, 6);
+
+DECL_BITFIELD(GBADebugFlags, uint16_t);
+DECL_BITS(GBADebugFlags, Level, 0, 3);
+DECL_BIT(GBADebugFlags, Send, 8);
 
 struct GBATimer {
 	uint16_t reload;
@@ -120,6 +125,10 @@
 	bool realisticTiming;
 	bool hardCrash;
 	bool allowOpposingDirections;
+
+	bool debug;
+	char debugString[0x100];
+	GBADebugFlags debugFlags;
 };
 
 struct GBACartridge {
@@ -153,6 +162,7 @@ void GBARaiseIRQ(struct GBA* gba, enum GBAIRQ irq);
 void GBATestIRQ(struct ARMCore* cpu);
 void GBAHalt(struct GBA* gba);
 void GBAStop(struct GBA* gba);
+void GBADebug(struct GBA* gba, uint16_t value);
 
 void GBAAttachDebugger(struct GBA* gba, struct mDebugger* debugger);
 void GBADetachDebugger(struct GBA* gba);

@@ -540,7 +540,20 @@ break;
 		case REG_MAX:
 			// Some bad interrupt libraries will write to this
 			break;
+		case REG_DEBUG_ENABLE:
+			gba->debug = value == 0xC0DE;
+			return;
+		case REG_DEBUG_FLAGS:
+			if (gba->debug) {
+				GBADebug(gba, value);
+				return;
+			}
+			// Fall through
 		default:
+			if (address >= REG_DEBUG_STRING && address - REG_DEBUG_STRING < sizeof(gba->debugString)) {
+				STORE_16LE(value, address - REG_DEBUG_STRING, gba->debugString);
+				return;
+			}
 			mLOG(GBA_IO, STUB, "Stub I/O register write: %03X", address);
 			if (address >= REG_MAX) {
 				mLOG(GBA_IO, GAME_ERROR, "Write to unused I/O register: %03X", address);
@@ -560,6 +573,10 @@ GBAHalt(gba);
 		} else {
 			GBAStop(gba);
 		}
+		return;
+	}
+	if (address >= REG_DEBUG_STRING && address - REG_DEBUG_STRING < sizeof(gba->debugString)) {
+		gba->debugString[address - REG_DEBUG_STRING] = value;
 		return;
 	}
 	if (address > SIZE_IO) {
@@ -613,6 +630,10 @@ case REG_DMA3DAD_LO:
 		value = GBAMemoryWriteDMADAD(gba, 3, value);
 		break;
 	default:
+		if (address >= REG_DEBUG_STRING && address - REG_DEBUG_STRING < sizeof(gba->debugString)) {
+			STORE_32LE(value, address - REG_DEBUG_STRING, gba->debugString);
+			return;
+		}
 		GBAIOWrite(gba, address, value & 0xFFFF);
 		GBAIOWrite(gba, address | 2, value >> 16);
 		return;
@@ -848,6 +869,11 @@ case 0x86:
 	case 0x8A:
 		mLOG(GBA_IO, GAME_ERROR, "Read from unused I/O register: %03X", address);
 		return 0;
+	case REG_DEBUG_ENABLE:
+		if (gba->debug) {
+			return 0x1DEA;
+		}
+		// Fall through
 	default:
 		mLOG(GBA_IO, GAME_ERROR, "Read from unused I/O register: %03X", address);
 		return GBALoadBad(gba->cpu);

@@ -150,7 +150,11 @@
 	REG_MAX = 0x20A,
 
 	REG_POSTFLG = 0x300,
-	REG_HALTCNT = 0x301
+	REG_HALTCNT = 0x301,
+
+	REG_DEBUG_STRING = 0xFFF600,
+	REG_DEBUG_FLAGS = 0xFFF700,
+	REG_DEBUG_ENABLE = 0xFFF780,
 };
 
 mLOG_DECLARE_CATEGORY(GBA_IO);