GBA Hardware: RTC accuracy improvements

CHANGES

@@ -47,6 +47,7 @@ Bugfixes:
  - PSP2: Fix issues causing poor audio
  - Wii: Fix screen tear when unpausing
  - GBA: Fix some GBA ROM misdetection (fixes mgba.io/i/978)
+ - GBA Hardware: RTC accuracy improvements
 Misc:
  - GBA Timer: Use global cycles for timers
  - GBA: Extend oddly-sized ROMs to full address space (fixes mgba.io/i/722)

src/gba/hardware.c

@@ -67,7 +67,7 @@ void GBAHardwareInit(struct GBACartridgeHardware* hw, uint16_t* base) {
 
 void GBAHardwareClear(struct GBACartridgeHardware* hw) {
 	hw->devices = HW_NONE | (hw->devices & HW_GB_PLAYER_DETECTION);
-	hw->direction = GPIO_WRITE_ONLY;
+	hw->readWrite = GPIO_WRITE_ONLY;
 	hw->pinState = 0;
 	hw->direction = 0;
 
@@ -83,7 +83,7 @@ void GBAHardwareGPIOWrite(struct GBACartridgeHardware* hw, uint32_t address, uin
 	switch (address) {
 	case GPIO_REG_DATA:
 		hw->pinState &= ~hw->direction;
-		hw->pinState |= value;
+		hw->pinState |= value & hw->direction;
 		_readPins(hw);
 		break;
 	case GPIO_REG_DIRECTION:
@@ -96,13 +96,13 @@ void GBAHardwareGPIOWrite(struct GBACartridgeHardware* hw, uint32_t address, uin
 		mLOG(GBA_HW, WARN, "Invalid GPIO address");
 	}
 	if (hw->readWrite) {
-		uint16_t old;
-		LOAD_16(old, 0, hw->gpioBase);
-		old &= ~hw->direction;
-		old |= hw->pinState;
-		STORE_16(old, 0, hw->gpioBase);
+		STORE_16(hw->pinState, 0, hw->gpioBase);
+		STORE_16(hw->direction, 2, hw->gpioBase);
+		STORE_16(hw->readWrite, 4, hw->gpioBase);
 	} else {
 		hw->gpioBase[0] = 0;
+		hw->gpioBase[1] = 0;
+		hw->gpioBase[2] = 0;
 	}
 }
 
@@ -167,23 +167,21 @@ void _rtcReadPins(struct GBACartridgeHardware* hw) {
 		if ((hw->pinState & 5) == 1) {
 			hw->rtc.transferStep = 1;
 		}
+		_outputPins(hw, 1);
 		break;
 	case 1:
 		if ((hw->pinState & 5) == 5) {
 			hw->rtc.transferStep = 2;
 		}
+		_outputPins(hw, 5);
 		break;
 	case 2:
 		if (!(hw->pinState & 1)) {
 			hw->rtc.bits &= ~(1 << hw->rtc.bitsRead);
 			hw->rtc.bits |= ((hw->pinState & 2) >> 1) << hw->rtc.bitsRead;
 		} else {
 			if (hw->pinState & 4) {
-				// GPIO direction should always != reading
-				if (hw->direction & 2) {
-					if (RTCCommandDataIsReading(hw->rtc.command)) {
-						mLOG(GBA_HW, GAME_ERROR, "Attempting to write to RTC while in read mode");
-					}
+				if (!RTCCommandDataIsReading(hw->rtc.command)) {
 					++hw->rtc.bitsRead;
 					if (hw->rtc.bitsRead == 8) {
 						_rtcProcessByte(hw);
@@ -195,7 +193,7 @@ void _rtcReadPins(struct GBACartridgeHardware* hw) {
 						--hw->rtc.bytesRemaining;
 						if (hw->rtc.bytesRemaining <= 0) {
 							hw->rtc.commandActive = 0;
-							hw->rtc.command = RTCCommandDataClearReading(hw->rtc.command);
+							hw->rtc.command = 0;
 						}
 						hw->rtc.bitsRead = 0;
 					}
@@ -204,8 +202,9 @@ void _rtcReadPins(struct GBACartridgeHardware* hw) {
 				hw->rtc.bitsRead = 0;
 				hw->rtc.bytesRemaining = 0;
 				hw->rtc.commandActive = 0;
-				hw->rtc.command = RTCCommandDataClearReading(hw->rtc.command);
+				hw->rtc.command = 0;
 				hw->rtc.transferStep = 0;
+				_outputPins(hw, 1);
 			}
 		}
 		break;
@@ -256,12 +255,16 @@ void _rtcProcessByte(struct GBACartridgeHardware* hw) {
 	hw->rtc.bitsRead = 0;
 	if (!hw->rtc.bytesRemaining) {
 		hw->rtc.commandActive = 0;
-		hw->rtc.command = RTCCommandDataClearReading(hw->rtc.command);
+		hw->rtc.command = 0;
 	}
 }
 
 unsigned _rtcOutput(struct GBACartridgeHardware* hw) {
 	uint8_t outputByte = 0;
+	if (!hw->rtc.commandActive) {
+		mLOG(GBA_HW, GAME_ERROR, "Attempting to use RTC without an active command");
+		return 0;
+	}
 	switch (RTCCommandDataGetCommand(hw->rtc.command)) {
 	case RTC_CONTROL:
 		outputByte = hw->rtc.control;