diff --git a/CMakeLists.txt b/CMakeLists.txt
index 3d5801063..ef487f075 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -21,10 +21,11 @@ file(GLOB GBA_SV_SRC ${CMAKE_SOURCE_DIR}/src/gba/supervisor/*.c)
 file(GLOB UTIL_SRC ${CMAKE_SOURCE_DIR}/src/util/*.[cSs])
 file(GLOB VFS_SRC ${CMAKE_SOURCE_DIR}/src/util/vfs/*.c)
 file(GLOB RENDERER_SRC ${CMAKE_SOURCE_DIR}/src/gba/renderers/video-software.c)
+file(GLOB SIO_SRC ${CMAKE_SOURCE_DIR}/src/gba/sio/lockstep.c)
 file(GLOB THIRD_PARTY_SRC ${CMAKE_SOURCE_DIR}/src/third-party/inih/*.c)
 list(APPEND UTIL_SRC ${CMAKE_SOURCE_DIR}/src/platform/commandline.c)
 source_group("ARM core" FILES ${ARM_SRC})
-source_group("GBA board" FILES ${GBA_SRC} ${RENDERER_SRC})
+source_group("GBA board" FILES ${GBA_SRC} ${RENDERER_SRC} ${SIO_SRC})
 source_group("GBA supervisor" FILES ${GBA_SV_SRC})
 source_group("Utilities" FILES ${UTIL_SRC} ${VFS_SRC}})
 include_directories(${CMAKE_SOURCE_DIR}/src/arm)
@@ -275,6 +276,7 @@ set(SRC
 	${GBA_SV_SRC}
 	${DEBUGGER_SRC}
 	${RENDERER_SRC}
+	${SIO_SRC}
 	${UTIL_SRC}
 	${VFS_SRC}
 	${OS_SRC}
diff --git a/src/gba/sio.h b/src/gba/sio.h
index 030218cc8..61e979385 100644
--- a/src/gba/sio.h
+++ b/src/gba/sio.h
@@ -30,11 +30,11 @@ struct GBASIO;
 struct GBASIODriver {
 	struct GBASIO* p;
 
-	int (*init)(struct GBASIODriver* driver);
+	bool (*init)(struct GBASIODriver* driver);
 	void (*deinit)(struct GBASIODriver* driver);
-	int (*load)(struct GBASIODriver* driver);
-	int (*unload)(struct GBASIODriver* driver);
-	int (*writeRegister)(struct GBASIODriver* driver, uint32_t address, uint16_t value);
+	bool (*load)(struct GBASIODriver* driver);
+	bool (*unload)(struct GBASIODriver* driver);
+	uint16_t (*writeRegister)(struct GBASIODriver* driver, uint32_t address, uint16_t value);
 	int32_t (*processEvents)(struct GBASIODriver* driver, int32_t cycles);
 };
 
diff --git a/src/gba/sio/lockstep.c b/src/gba/sio/lockstep.c
new file mode 100644
index 000000000..d7cfa268e
--- /dev/null
+++ b/src/gba/sio/lockstep.c
@@ -0,0 +1,73 @@
+/* Copyright (c) 2013-2015 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 "lockstep.h"
+
+#define LOCKSTEP_INCREMENT 2048
+
+static bool GBASIOLockstepNodeInit(struct GBASIODriver* driver);
+static void GBASIOLockstepNodeDeinit(struct GBASIODriver* driver);
+static bool GBASIOLockstepNodeLoad(struct GBASIODriver* driver);
+static bool GBASIOLockstepNodeUnload(struct GBASIODriver* driver);
+static uint16_t GBASIOLockstepNodeWriteRegister(struct GBASIODriver* driver, uint32_t address, uint16_t value);
+static int32_t GBASIOLockstepNodeProcessEvents(struct GBASIODriver* driver, int32_t cycles);
+
+void GBASIOLockstepInit(struct GBASIOLockstep* lockstep) {
+	lockstep->players[0] = 0;
+	lockstep->players[1] = 0;
+	lockstep->players[2] = 0;
+	lockstep->players[3] = 0;
+	lockstep->attached = 0;
+	ConditionInit(&lockstep->barrier);
+}
+
+void GBASIOLockstepDeinit(struct GBASIOLockstep* lockstep) {
+	ConditionDeinit(&lockstep->barrier);
+}
+
+void GBASIOLockstepNodeCreate(struct GBASIOLockstepNode* node) {
+	node->d.init = GBASIOLockstepNodeInit;
+	node->d.deinit = GBASIOLockstepNodeDeinit;
+	node->d.load = GBASIOLockstepNodeLoad;
+	node->d.unload = GBASIOLockstepNodeUnload;
+	node->d.writeRegister = GBASIOLockstepNodeWriteRegister;
+	node->d.processEvents = GBASIOLockstepNodeProcessEvents;
+}
+
+bool GBASIOLockstepAttachNode(struct GBASIOLockstep* lockstep, struct GBASIOLockstepNode* node) {
+	if (lockstep->attached == MAX_GBAS) {
+		return false;
+	}
+	lockstep->players[lockstep->attached] = node;
+	++lockstep->attached;
+	return true;
+}
+
+bool GBASIOLockstepNodeInit(struct GBASIODriver* driver) {
+	UNUSED(driver);
+	return true;
+}
+
+void GBASIOLockstepNodeDeinit(struct GBASIODriver* driver) {
+	UNUSED(driver);
+}
+
+bool GBASIOLockstepNodeLoad(struct GBASIODriver* driver) {
+	UNUSED(driver);
+	return true;
+}
+
+bool GBASIOLockstepNodeUnload(struct GBASIODriver* driver) {
+	UNUSED(driver);
+	return true;
+}
+
+static uint16_t GBASIOLockstepNodeWriteRegister(struct GBASIODriver* driver, uint32_t address, uint16_t value) {
+	return value;
+}
+
+static int32_t GBASIOLockstepNodeProcessEvents(struct GBASIODriver* driver, int32_t cycles) {
+	return INT_MAX;
+}
diff --git a/src/gba/sio/lockstep.h b/src/gba/sio/lockstep.h
new file mode 100644
index 000000000..c25025db6
--- /dev/null
+++ b/src/gba/sio/lockstep.h
@@ -0,0 +1,32 @@
+/* Copyright (c) 2013-2015 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 SIO_LOCKSTEP_H
+#define SIO_LOCKSTEP_H
+
+#include "gba/sio.h"
+
+#include "util/threading.h"
+
+struct GBASIOLockstep {
+	struct GBASIOLockstepNode* players[MAX_GBAS];
+	int attached;
+
+	uint16_t data[MAX_GBAS];
+	Condition barrier;
+};
+
+struct GBASIOLockstepNode {
+	struct GBASIODriver d;
+	struct GBASIOLockstep* p;
+};
+
+void GBASIOLockstepInit(struct GBASIOLockstep*);
+void GBASIOLockstepDeinit(struct GBASIOLockstep*);
+
+void GBASIOLockstepNodeCreate(struct GBASIOLockstepNode*);
+bool GBASIOLockstepAttachNode(struct GBASIOLockstep*, struct GBASIOLockstepNode*);
+
+#endif
diff --git a/src/platform/qt/CMakeLists.txt b/src/platform/qt/CMakeLists.txt
index 531ab4886..f87fa093b 100644
--- a/src/platform/qt/CMakeLists.txt
+++ b/src/platform/qt/CMakeLists.txt
@@ -51,6 +51,7 @@ set(SOURCE_FILES
 	KeyEditor.cpp
 	LoadSaveState.cpp
 	LogView.cpp
+	MultiplayerController.cpp
 	OverrideView.cpp
 	SavestateButton.cpp
 	SensorView.cpp
diff --git a/src/platform/qt/MultiplayerController.cpp b/src/platform/qt/MultiplayerController.cpp
new file mode 100644
index 000000000..99b1ee8e0
--- /dev/null
+++ b/src/platform/qt/MultiplayerController.cpp
@@ -0,0 +1,20 @@
+/* Copyright (c) 2013-2015 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 "MultiplayerController.h"
+
+using namespace QGBA;
+
+MultiplayerController::MultiplayerController() {
+	GBASIOLockstepInit(&m_lockstep);
+}
+
+MultiplayerController::~MultiplayerController() {
+	GBASIOLockstepDeinit(&m_lockstep);
+}
+
+bool MultiplayerController::attachGame(GameController* controller) {
+	return false;
+}
diff --git a/src/platform/qt/MultiplayerController.h b/src/platform/qt/MultiplayerController.h
new file mode 100644
index 000000000..3a10d56f0
--- /dev/null
+++ b/src/platform/qt/MultiplayerController.h
@@ -0,0 +1,29 @@
+/* Copyright (c) 2013-2015 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 QGBA_MULTIPLAYER_CONTROLLER
+#define QGBA_MULTIPLAYER_CONTROLLER
+
+extern "C" {
+#include "gba/sio/lockstep.h"
+}
+
+namespace QGBA {
+
+class GameController;
+
+class MultiplayerController {
+public:
+	MultiplayerController();
+	~MultiplayerController();
+
+	bool attachGame(GameController*);
+
+private:
+	GBASIOLockstep m_lockstep;
+};
+
+}
+#endif