@@ -54,6 +54,9 @@
 	gb->audio.p = gb;
 	GBAudioInit(&gb->audio, 2048, &gb->memory.io[REG_NR52], GB_AUDIO_DMG); // TODO: Remove magic constant
 
+	gb->sio.p = gb;
+	GBSIOInit(&gb->sio);
+
 	gb->timer.p = gb;
 
 	gb->biosVf = 0;
@@ -163,6 +166,8 @@ void GBDestroy(struct GB* gb) {
 	GBUnloadROM(gb);
 
 	GBMemoryDeinit(gb);
+	GBVideoDeinit(&gb->video);
+	GBSIODeinit(&gb->sio);
 }
 
 void GBInterruptHandlerInit(struct LR35902InterruptHandler* irqh) {
@@ -256,6 +261,7 @@ GBVideoReset(&gb->video);
 	GBTimerReset(&gb->timer);
 	GBIOReset(gb);
 	GBAudioReset(&gb->audio);
+	GBSIOReset(&gb->sio);
 }
 
 void GBUpdateIRQs(struct GB* gb) {
@@ -328,6 +334,11 @@ }
 		}
 
 		testEvent = GBTimerProcessEvents(&gb->timer, cycles);
+		if (testEvent < nextEvent) {
+			nextEvent = testEvent;
+		}
+
+		testEvent = GBSIOProcessEvents(&gb->sio, cycles);
 		if (testEvent < nextEvent) {
 			nextEvent = testEvent;
 		}

@@ -15,6 +15,7 @@
 #include "gb/audio.h"
 #include "gb/interface.h"
 #include "gb/memory.h"
+#include "gb/sio.h"
 #include "gb/timer.h"
 #include "gb/video.h"
 
@@ -51,6 +52,7 @@ struct GBMemory memory;
 	struct GBVideo video;
 	struct GBTimer timer;
 	struct GBAudio audio;
+	struct GBSIO sio;
 	enum GBModel model;
 
 	struct mCoreSync* sync;

@@ -6,6 +6,7 @@ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 #include "io.h"
 
 #include "gb/gb.h"
+#include "gb/sio.h"
 #include "gb/serialize.h"
 
 mLOG_DEFINE_CATEGORY(GB_IO, "GB I/O");
@@ -157,6 +158,9 @@ }
 
 void GBIOWrite(struct GB* gb, unsigned address, uint8_t value) {
 	switch (address) {
+	case REG_SC:
+		GBSIOWriteSC(&gb->sio, value);
+		break;
 	case REG_DIV:
 		GBTimerDivReset(&gb->timer);
 		return;
@@ -334,6 +338,7 @@ gb->audio.ch3.wavedata8[gb->audio.ch3.window >> 1] = value;
 		}
 		break;
 	case REG_JOYP:
+	case REG_SB:
 	case REG_TIMA:
 	case REG_TMA:
 	case REG_LYC:
@@ -461,10 +466,6 @@ uint8_t GBIORead(struct GB* gb, unsigned address) {
 	switch (address) {
 	case REG_JOYP:
 		return _readKeys(gb);
-	case REG_SB:
-	case REG_SC:
-		// TODO
-		break;
 	case REG_IE:
 		return gb->memory.ie;
 	case REG_WAVE_0:
@@ -493,6 +494,8 @@ } else {
 			return gb->audio.ch3.wavedata8[address - REG_WAVE_0];
 		}
 		break;
+	case REG_SB:
+	case REG_SC:
 	case REG_IF:
 	case REG_NR10:
 	case REG_NR11:

@@ -0,0 +1,53 @@
+/* Copyright (c) 2013-2016 Jeffrey Pfau
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+#include "sio.h"
+
+#include "gb/gb.h"
+#include "gb/io.h"
+#include "gb/serialize.h"
+
+void GBSIOInit(struct GBSIO* sio) {
+	sio->pendingSB = 0xFF;
+}
+
+void GBSIOReset(struct GBSIO* sio) {
+	sio->nextEvent = INT_MAX;
+	sio->remainingBits = 0;
+}
+
+void GBSIODeinit(struct GBSIO* sio) {
+	UNUSED(sio);
+	// Nothing to do yet
+}
+
+int32_t GBSIOProcessEvents(struct GBSIO* sio, int32_t cycles) {
+	if (sio->nextEvent != INT_MAX) {
+		sio->nextEvent -= cycles;
+	}
+	if (sio->nextEvent <= 0) {
+		--sio->remainingBits;
+		sio->p->memory.io[REG_SB] &= ~(8 >> sio->remainingBits);
+		sio->p->memory.io[REG_SB] |= sio->pendingSB & ~(8 >> sio->remainingBits);
+		if (!sio->remainingBits) {
+			sio->p->memory.io[REG_IF] |= (1 << GB_IRQ_SIO);
+			sio->p->memory.io[REG_SC] = GBRegisterSCClearEnable(sio->p->memory.io[REG_SC]);
+			GBUpdateIRQs(sio->p);
+			sio->nextEvent = INT_MAX;
+		} else {
+			sio->nextEvent += sio->period;
+		}
+	}
+	return sio->nextEvent;
+}
+
+void GBSIOWriteSC(struct GBSIO* sio, uint8_t sc) {
+	sio->period = 0x1000; // TODO Shift Clock
+	if (GBRegisterSCIsEnable(sc)) {
+		sio->nextEvent = sio->p->cpu->cycles + sio->period;
+		sio->remainingBits = 8;
+	}
+}
+

@@ -0,0 +1,33 @@
+/* Copyright (c) 2013-2016 Jeffrey Pfau
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+#ifndef GB_SIO_H
+#define GB_SIO_H
+
+#include "util/common.h"
+
+struct GB;
+struct GBSIO {
+	struct GB* p;
+
+	int32_t nextEvent;
+	int32_t period;
+	int remainingBits;
+
+	uint8_t pendingSB;
+};
+
+DECL_BITFIELD(GBRegisterSC, uint8_t);
+DECL_BIT(GBRegisterSC, ShiftClock, 0);
+DECL_BIT(GBRegisterSC, ClockSpeed, 1);
+DECL_BIT(GBRegisterSC, Enable, 7);
+
+void GBSIOInit(struct GBSIO* sio);
+void GBSIOReset(struct GBSIO* sio);
+void GBSIODeinit(struct GBSIO* sio);
+int32_t GBSIOProcessEvents(struct GBSIO* sio, int32_t cycles);
+void GBSIOWriteSC(struct GBSIO* sio, uint8_t sc);
+
+#endif