diff --git a/src/gba/sio.c b/src/gba/sio.c
index 363c431cc..84f4962ed 100644
--- a/src/gba/sio.c
+++ b/src/gba/sio.c
@@ -31,6 +31,23 @@ static struct GBASIODriver* _lookupDriver(struct GBASIO* sio, enum GBASIOMode mo
 	}
 }
 
+static const char* _modeName(enum GBASIOMode mode) {
+	switch (mode) {
+	case SIO_NORMAL_8:
+		return "NORMAL8";
+	case SIO_NORMAL_32:
+		return "NORMAL32";
+	case SIO_MULTI:
+		return "MULTI";
+	case SIO_JOYBUS:
+		return "JOYBUS";
+	case SIO_GPIO:
+		return "GPIO";
+	default:
+		return "(unknown)";
+	}
+}
+
 static void _switchMode(struct GBASIO* sio) {
 	unsigned mode = ((sio->rcnt & 0xC000) | (sio->siocnt & 0x3000)) >> 12;
 	enum GBASIOMode newMode;
@@ -43,6 +60,7 @@ static void _switchMode(struct GBASIO* sio) {
 		if (sio->activeDriver && sio->activeDriver->unload) {
 			sio->activeDriver->unload(sio->activeDriver);
 		}
+		mLOG(GBA_SIO, DEBUG, "Switching mode from %s to %s", _modeName(sio->mode), _modeName(newMode));
 		sio->mode = newMode;
 		sio->activeDriver = _lookupDriver(sio, sio->mode);
 		if (sio->activeDriver && sio->activeDriver->load) {
diff --git a/src/gba/sio/joybus.c b/src/gba/sio/joybus.c
index c5a339883..7b4f9e207 100644
--- a/src/gba/sio/joybus.c
+++ b/src/gba/sio/joybus.c
@@ -21,9 +21,22 @@ void GBASIOJOYCreate(struct GBASIODriver* sio) {
 uint16_t GBASIOJOYWriteRegister(struct GBASIODriver* sio, uint32_t address, uint16_t value) {
 	switch (address) {
 	case REG_JOYCNT:
+		mLOG(GBA_SIO, DEBUG, "JOY write: CNT <- %04X", value);
 		return (value & 0x0040) | (sio->p->p->memory.io[REG_JOYCNT >> 1] & ~(value & 0x7) & ~0x0040);
 	case REG_JOYSTAT:
+		mLOG(GBA_SIO, DEBUG, "JOY write: STAT <- %04X", value);
 		return (value & 0x0030) | (sio->p->p->memory.io[REG_JOYSTAT >> 1] & ~0x30);
+	case REG_JOY_TRANS_LO:
+		mLOG(GBA_SIO, DEBUG, "JOY write: TRANS_LO <- %04X", value);
+		break;
+	case REG_JOY_TRANS_HI:
+		mLOG(GBA_SIO, DEBUG, "JOY write: TRANS_HI <- %04X", value);
+		break;
+	default:
+		mLOG(GBA_SIO, DEBUG, "JOY write: Unknown reg %03X <- %04X", address, value);
+		// Fall through
+	case REG_RCNT:
+		break;
 	}
 	return value;
 }