@@ -55,7 +55,7 @@ file(GLOB UTIL_SRC ${CMAKE_CURRENT_SOURCE_DIR}/src/util/*.[cSs])
 file(GLOB UTIL_TEST_SRC ${CMAKE_CURRENT_SOURCE_DIR}/src/util/test/*.c)
 file(GLOB GUI_SRC ${CMAKE_CURRENT_SOURCE_DIR}/src/util/gui/*.c ${CMAKE_CURRENT_SOURCE_DIR}/src/feature/gui/*.c)
 file(GLOB GBA_RENDERER_SRC ${CMAKE_CURRENT_SOURCE_DIR}/src/gba/renderers/*.c)
-file(GLOB GBA_SIO_SRC ${CMAKE_CURRENT_SOURCE_DIR}/src/gba/sio/lockstep.c)
+file(GLOB GBA_SIO_SRC ${CMAKE_CURRENT_SOURCE_DIR}/src/gba/sio/*.c)
 file(GLOB GBA_EXTRA_SRC ${CMAKE_CURRENT_SOURCE_DIR}/src/gba/extra/*.c)
 file(GLOB GB_SIO_SRC ${CMAKE_CURRENT_SOURCE_DIR}/src/gb/sio/*.c)
 file(GLOB GB_RENDERER_SRC ${CMAKE_CURRENT_SOURCE_DIR}/src/gb/renderers/*.c)

@@ -21,6 +21,13 @@ SIO_GPIO = 8,
 	SIO_JOYBUS = 12
 };
 
+enum GBASIOJOYCommand {
+	JOY_RESET = 0xFF,
+	JOY_POLL = 0x00,
+	JOY_TRANS = 0x14,
+	JOY_RECV = 0x15
+};
+
 struct GBA;
 struct GBAAudio;
 struct GBASIO;
@@ -47,6 +54,10 @@ bool (*load)(struct GBASIODriver* driver);
 	bool (*unload)(struct GBASIODriver* driver);
 	uint16_t (*writeRegister)(struct GBASIODriver* driver, uint32_t address, uint16_t value);
 };
+
+void GBASIOJOYCreate(struct GBASIODriver* sio);
+int GBASIOJOYSendCommand(struct GBASIODriver* sio, enum GBASIOJOYCommand command, uint8_t* data);
+
 
 CXX_GUARD_END
 

@@ -0,0 +1,76 @@
+/* Copyright (c) 2013-2017 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 <mgba/internal/gba/sio.h>
+
+#include <mgba/internal/gba/gba.h>
+#include <mgba/internal/gba/io.h>
+
+static uint16_t GBASIOJOYWriteRegister(struct GBASIODriver* sio, uint32_t address, uint16_t value);
+
+void GBASIOJOYCreate(struct GBASIODriver* sio) {
+	sio->init = NULL;
+	sio->deinit = NULL;
+	sio->load = NULL;
+	sio->unload = NULL;
+	sio->writeRegister = GBASIOJOYWriteRegister;
+}
+
+uint16_t GBASIOJOYWriteRegister(struct GBASIODriver* sio, uint32_t address, uint16_t value) {
+	switch (address) {
+	case REG_JOYCNT:
+		return (value & 0x0040) | (sio->p->p->memory.io[REG_JOYCNT >> 1] & ~(value & 0x7) & ~0x0040);
+	case REG_JOYSTAT:
+		return (value & 0x0030) | (sio->p->p->memory.io[REG_JOYSTAT >> 1] & ~0x30);
+	case REG_JOY_TRANS_LO:
+	case REG_JOY_TRANS_HI:
+		sio->p->p->memory.io[REG_JOYSTAT >> 1] |= 8;
+		break;
+	}
+	return value;
+}
+
+int GBASIOJOYSendCommand(struct GBASIODriver* sio, enum GBASIOJOYCommand command, uint8_t* data) {
+	switch (command) {
+	case JOY_RESET:
+		sio->p->p->memory.io[REG_JOYCNT >> 1] |= 1;
+		if (sio->p->p->memory.io[REG_JOYCNT >> 1] & 0x40) {
+			GBARaiseIRQ(sio->p->p, IRQ_SIO);
+		}
+		// Fall through
+	case JOY_POLL:
+		data[0] = 0x00;
+		data[1] = 0x04;
+		data[2] = sio->p->p->memory.io[REG_JOYSTAT >> 1];
+		return 3;
+	case JOY_RECV:
+		sio->p->p->memory.io[REG_JOYCNT >> 1] |= 2;
+		sio->p->p->memory.io[REG_JOYSTAT >> 1] |= 2;
+
+		sio->p->p->memory.io[REG_JOY_RECV_LO >> 1] = data[0] | (data[1] << 8);
+		sio->p->p->memory.io[REG_JOY_RECV_HI >> 1] = data[2] | (data[3] << 8);
+
+		data[0] = sio->p->p->memory.io[REG_JOYSTAT >> 1];
+
+		if (sio->p->p->memory.io[REG_JOYCNT >> 1] & 0x40) {
+			GBARaiseIRQ(sio->p->p, IRQ_SIO);
+		}
+		return 1;
+	case JOY_TRANS:
+		sio->p->p->memory.io[REG_JOYCNT >> 1] |= 4;
+		sio->p->p->memory.io[REG_JOYSTAT >> 1] &= ~8;
+		data[0] = sio->p->p->memory.io[REG_JOY_TRANS_LO >> 1];
+		data[1] = sio->p->p->memory.io[REG_JOY_TRANS_LO >> 1] >> 8;
+		data[2] = sio->p->p->memory.io[REG_JOY_TRANS_HI >> 1];
+		data[3] = sio->p->p->memory.io[REG_JOY_TRANS_HI >> 1] >> 8;
+		data[4] = sio->p->p->memory.io[REG_JOYSTAT >> 1];
+
+		if (sio->p->p->memory.io[REG_JOYCNT >> 1] & 0x40) {
+			GBARaiseIRQ(sio->p->p, IRQ_SIO);
+		}
+		return 5;
+	}
+	return 0;
+}

@@ -53,6 +53,7 @@ #ifdef USE_PNG
 #include <mgba-util/png-io.h>
 #endif
 #ifdef M_CORE_GBA
+#include <mgba/gba/interface.h>
 #include <mgba/internal/arm/arm.h>
 #include <mgba/internal/gba/gba.h>
 #include <mgba/internal/gba/input.h>

@@ -30,6 +30,7 @@ #include <mgba/core/mem-search.h>
 #include <mgba/core/thread.h>
 #include <mgba/core/version.h>
 #include <mgba/debugger/debugger.h>
+#include <mgba/gba/interface.h>
 #include <mgba/internal/arm/arm.h>
 #include <mgba/internal/debugger/cli-debugger.h>
 #include <mgba/internal/gba/gba.h>

@@ -26,6 +26,7 @@ SIO_NORMAL_8 = lib.SIO_NORMAL_8
     SIO_NORMAL_32 = lib.SIO_NORMAL_32
     SIO_MULTI = lib.SIO_MULTI
     SIO_UART = lib.SIO_UART
+    SIO_JOYBUS = lib.SIO_JOYBUS
     SIO_GPIO = lib.SIO_GPIO
 
     def __init__(self, native):
@@ -82,6 +83,32 @@ return True
 
     def writeRegister(self, address, value):
         return value
+
+class GBASIOJOYDriver(GBASIODriver):
+    RESET = lib.JOY_RESET
+    POLL = lib.JOY_POLL
+    TRANS = lib.JOY_TRANS
+    RECV = lib.JOY_RECV
+
+    def __init__(self):
+        self._handle = ffi.new_handle(self)
+        self._native = ffi.gc(lib.GBASIOJOYPythonDriverCreate(self._handle), lib.free)
+
+    def sendCommand(self, cmd, data):
+        buffer = ffi.new('uint8_t[5]')
+        try:
+            buffer[0] = data[0]
+            buffer[1] = data[1]
+            buffer[2] = data[2]
+            buffer[3] = data[3]
+            buffer[4] = data[4]
+        except IndexError:
+            pass
+
+        outlen = lib.GBASIOJOYSendCommand(self._native, cmd, buffer)
+        if outlen > 0 and outlen <= 5:
+            return bytes(buffer[0:outlen])
+        return None
 
 class GBAMemory(Memory):
     def __init__(self, core, romSize=lib.SIZE_CART0):

@@ -46,6 +46,18 @@ driver->pyobj = pyobj;
 	return &driver->d;
 }
 
+struct GBASIODriver* GBASIOJOYPythonDriverCreate(void* pyobj) {
+	struct GBASIOPythonDriver* driver = malloc(sizeof(*driver));
+	GBASIOJOYCreate(&driver->d);
+	driver->d.init = _pyGBASIOPythonDriverInitShim;
+	driver->d.deinit = _pyGBASIOPythonDriverDeinitShim;
+	driver->d.load = _pyGBASIOPythonDriverLoadShim;
+	driver->d.unload = _pyGBASIOPythonDriverUnloadShim;
+
+	driver->pyobj = pyobj;
+	return &driver->d;
+}
+
 #endif
 
 #ifdef M_CORE_GB

@@ -13,6 +13,7 @@ void* pyobj;
 };
 
 struct GBASIODriver* GBASIOPythonDriverCreate(void* pyobj);
+struct GBASIODriver* GBASIOJOYPythonDriverCreate(void* pyobj);
 
 PYEXPORT bool _pyGBASIOPythonDriverInit(void* driver);
 PYEXPORT void _pyGBASIOPythonDriverDeinit(void* driver);