Arduino 6502 ROM Emulator

ROM.ino

const char sAddrBus[] = { 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52 };
const char sDataBus[] = { 39, 41, 43, 45, 47, 49, 51, 53 };

#define	qPinClock			2
#define	qPinRW				3

const uint8_t	sROM[] =
{
//00		0xFEFF
	0xa2, 0x05, 0xca, 0xd0, 0xfd, 0xea, 0xea, 0xea,   0xa2, 0x04, 0xca, 0xd0, 0xfd, 0x4c, 0x00, 0xff,
// 	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,

//64
	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,

//128
	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,

//192
	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00, 0x00, 0xFF, 0x00, 0x00,

//256
// 	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
// 	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
// 	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
// 	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
};
const uint16_t	kROMStartAddr = 0x0000 - sizeof(sROM);

uint8_t			sRAM[1024];

void
setup()
{
	for (int i = 0; i < sizeof(sAddrBus); i++)
	{
		pinMode(sAddrBus[i], INPUT);
	}
	
	for (int i = 0; i < sizeof(sDataBus); i++)
	{
		pinMode(sDataBus[i], INPUT);
	}
	
	pinMode(qPinClock, INPUT);
	attachInterrupt(digitalPinToInterrupt(qPinClock), onClock, RISING);

	pinMode(qPinRW, INPUT);

	
	Serial.begin(115200);
	Serial.println();
	Serial.println();
	Serial.println("6502 ROM Emulator");
	
	char s[32];
	snprintf(s, sizeof(s), "ROM Start: 0x%04X", kROMStartAddr);
	Serial.println(s);
	snprintf(s, sizeof(s), "ROM End:   0x%04X", kROMStartAddr + sizeof(sROM));
	Serial.println(s);
}

void
setDataBusDirection(bool inRead)
{
	int mode = inRead ? OUTPUT : INPUT;
	for (int i = 0; i < sizeof(sDataBus); i++)
	{
		pinMode(sDataBus[i], mode);
	}
}

void
setDataBus(uint8_t inData)
{
	for (int i = 0; i < sizeof(sDataBus); i++)
	{
		digitalWrite(sDataBus[i], inData & (1 << (7 - i)));
	}
}

uint16_t
readBus(const char* inBus, int inWidth)
{
	uint16_t value = 0;
	for (int i = 0; i < inWidth; i++)
	{
		int bit = digitalRead(inBus[i]) ? 1 : 0;
// 		Serial.print(bit);
		value = (value << 1) + bit;
	}
	
	return value;
}

void
onClock()
{
	static char s[64];
	
	//	If the processor is reading, output values…
	
	bool rw = digitalRead(qPinRW);
	setDataBusDirection(rw);
	
	uint16_t addr = readBus(sAddrBus, sizeof (sAddrBus));
	uint8_t data = 0;
	
	if (rw)	//	CPU is reading
	{
		if (addr >= kROMStartAddr)
		{
			int idx = addr - kROMStartAddr;
			data = sROM[idx];
			setDataBus(data);
			
// 			snprintf(s, sizeof(s), "Read from ROM 0x%04X (%4d): 0x%02X", addr, idx, data);
// 			Serial.println(s);
		}
		else
		{
			setDataBus(0xea);		//	NOP
		}
	}
	else	//	CPU is writing
	{
		//	TODO: Ignore for now
	}
	
	//	Log the bus state…
	
	data = readBus(sDataBus, sizeof (sDataBus));
	
	snprintf(s, sizeof(s), "0x%04X  %c 0x%02X", addr, rw ? 'r' : 'W', data);
	Serial.println(s);
}

void
loop()
{
}