@@ -0,0 +1,46 @@
+#include "gba.h"
+
+#include "gba-gpio.h"
+
+static void _readPins(struct GBACartridgeGPIO* gpio);
+
+static void _rtcReadPins(struct GBACartridgeGPIO* gpio);
+
+void GBAGPIOInit(struct GBACartridgeGPIO* gpio, uint16_t* base) {
+	gpio->gpioDevices = GPIO_NONE;
+	gpio->direction = GPIO_WRITE_ONLY;
+	gpio->gpioBase = base;
+	gpio->pinState = 0;
+	gpio->pinDirection = 0;
+}
+
+void GBAGPIOWrite(struct GBACartridgeGPIO* gpio, uint32_t address, uint16_t value) {
+	switch (address) {
+	case GPIO_REG_DATA:
+		gpio->pinState = value;
+		_readPins(gpio);
+		break;
+	case GPIO_REG_DIRECTION:
+		gpio->pinDirection = value;
+		break;
+	case GPIO_REG_CONTROL:
+		gpio->direction = value;
+		break;
+	default:
+		GBALog(0, GBA_LOG_WARN, "Invalid GPIO address");
+	}
+}
+
+void GBAGPIOInitRTC(struct GBACartridgeGPIO* gpio) {
+	// TODO
+}
+
+void _readPins(struct GBACartridgeGPIO* gpio) {
+	if (gpio->gpioDevices & GPIO_RTC) {
+		_rtcReadPins(gpio);
+	}
+}
+
+void _rtcReadPins(struct GBACartridgeGPIO* gpio) {
+	// TODO
+}

@@ -0,0 +1,64 @@
+#ifndef GBA_GPIO_H
+#define GBA_GPIO_H
+
+#include <stdint.h>
+
+#define IS_GPIO_REGISTER(reg) ((reg) == GPIO_REG_DATA || (reg) == GPIO_REG_DIRECTION || (reg) == GPIO_REG_CONTROL)
+
+enum GPIODevice {
+	GPIO_NONE = 0,
+	GPIO_RTC = 1,
+	GPIO_RUMBLE = 2,
+	GPIO_LIGHT_SENSOR = 4,
+	GPIO_GYRO = 8
+};
+
+enum GPIORegister {
+	GPIO_REG_DATA = 0xC4,
+	GPIO_REG_DIRECTION = 0xC6,
+	GPIO_REG_CONTROL = 0xC8
+};
+
+enum GPIODirection {
+	GPIO_WRITE_ONLY = 0,
+	GPIO_READ_WRITE = 1
+};
+
+struct GBARTC {
+	// TODO
+};
+
+struct GBACartridgeGPIO {
+	int gpioDevices;
+	enum GPIODirection direction;
+	uint16_t* gpioBase;
+
+	union {
+		struct {
+			unsigned p0 : 1;
+			unsigned p1 : 1;
+			unsigned p2 : 1;
+			unsigned p3 : 1;
+		};
+		uint16_t pinState;
+	};
+
+	union {
+		struct {
+			unsigned dir0 : 1;
+			unsigned dir1 : 1;
+			unsigned dir2 : 1;
+			unsigned dir3 : 1;			
+		};
+		uint16_t pinDirection;
+	};
+
+	struct GBARTC rtc;
+};
+
+void GBAGPIOInit(struct GBACartridgeGPIO* gpio, uint16_t* gpioBase);
+void GBAGPIOWrite(struct GBACartridgeGPIO* gpio, uint32_t address, uint16_t value);
+
+void GBAGPIOInitRTC(struct GBACartridgeGPIO* gpio);
+
+#endif

@@ -1,5 +1,6 @@
 #include "gba-memory.h"
 
+#include "gba-gpio.h"
 #include "gba-io.h"
 #include "hle-bios.h"
 
@@ -409,7 +410,12 @@ gbaMemory->p->video.oam.raw[(address & (SIZE_OAM - 1)) >> 1] = value;
 		gbaMemory->p->video.renderer->writeOAM(gbaMemory->p->video.renderer, (address & (SIZE_OAM - 1)) >> 1);
 		break;
 	case BASE_CART0:
-		GBALog(gbaMemory->p, GBA_LOG_STUB, "Unimplemented memory Store16: 0x%08X", address);
+		if (IS_GPIO_REGISTER(address & 0xFFFFFF)) {
+			uint32_t reg = address & 0xFFFFFF;
+			GBAGPIOWrite(&gbaMemory->gpio, reg, value);
+		} else {
+			GBALog(gbaMemory->p, GBA_LOG_GAME_ERROR, "Bad cartridge Store16: 0x%08X", address);
+		}
 		break;
 	case BASE_CART2_EX:
 		if (gbaMemory->savedata.type == SAVEDATA_NONE) {

@@ -3,6 +3,7 @@ #define GBA_MEMORY_H
 
 #include "arm.h"
 
+#include "gba-gpio.h"
 #include "gba-savedata.h"
 
 #include <string.h>
@@ -112,6 +113,7 @@ uint32_t* iwram;
 	uint32_t* rom;
 	uint16_t io[SIZE_IO >> 1];
 
+	struct GBACartridgeGPIO gpio;
 	struct GBASavedata savedata;
 	size_t romSize;
 	uint16_t romID;

@@ -68,11 +68,6 @@
 	enum FlashStateMachine flashState;
 };
 
-struct SavedataOverride {
-	uint32_t id;
-	enum SavedataType type;
-};
-
 void GBASavedataInit(struct GBASavedata* savedata, const char* filename);
 void GBASavedataDeinit(struct GBASavedata* savedata);
 

@@ -22,10 +22,16 @@ SP_BASE_IRQ = 0x03FFFFA0,
 	SP_BASE_SUPERVISOR = 0x03FFFFE0
 };
 
-static const struct SavedataOverride _savedataOverrides[] = {
-	{ 'E4XA', SAVEDATA_FLASH1M },
-	{ 'EEPB', SAVEDATA_FLASH1M },
-	{ 0, 0 }
+struct GBACartridgeOverride {
+	uint32_t id;
+	enum SavedataType type;
+	int gpio;
+};
+
+static const struct GBACartridgeOverride _overrides[] = {
+	{ 'E4XA', SAVEDATA_FLASH1M, GPIO_NONE },
+	{ 'EEPB', SAVEDATA_FLASH1M, GPIO_RTC },
+	{ 0, 0, 0 }
 };
 
 static void GBAProcessEvents(struct ARMBoard* board);
@@ -284,6 +290,7 @@ gba->memory.romSize = info.st_size;
 	if (gba->savefile) {
 		GBASavedataInit(&gba->memory.savedata, gba->savefile);
 	}
+	GBAGPIOInit(&gba->memory.gpio, &((uint16_t*) gba->memory.rom)[GPIO_REG_DATA >> 1]);
 	_checkOverrides(gba, ((struct GBACartridge*) gba->memory.rom)->id);
 	// TODO: error check
 }
@@ -455,10 +462,10 @@ }
 
 void _checkOverrides(struct GBA* gba, uint32_t id) {
 	int i;
-	for (i = 0; _savedataOverrides[i].id; ++i) {
-		if (_savedataOverrides[i].id == id) {
-			gba->memory.savedata.type = _savedataOverrides[i].type;
-			switch (_savedataOverrides[i].type) {
+	for (i = 0; _overrides[i].id; ++i) {
+		if (_overrides[i].id == id) {
+			gba->memory.savedata.type = _overrides[i].type;
+			switch (_overrides[i].type) {
 				case SAVEDATA_FLASH512:
 				case SAVEDATA_FLASH1M:
 					GBASavedataInitFlash(&gba->memory.savedata);
@@ -473,6 +480,10 @@ case SAVEDATA_NONE:
 					break;
 			}
 			return;
+
+			if (_overrides[i].gpio & GPIO_RTC) {
+				GBAGPIOInitRTC(&gba->memory.gpio);
+			}
 		}
 	}
 }