#include <At89x55.h>
#include <STDIO.h>
#define THRESHOLD 100

// Small busy-waiting loop
void wait(){
	unsigned int i;
	for (i=0; i<7; i++);
}

// Reads bytes produced by 4021-IC
void readPads(char *left, char *right){
	char i;

	// Load new inputs into parallel ports of 4021-IC on Nintendo controllers
	T2 = 1;  // Bring PL high
	wait();  // until stable
	T2 = 0;  // Latch the inputs on the falling edge

	// Retrive values.  Logical clock clocks bits out of 4021-IC into 8051
	for(i=0; i<8; i++){
		wait();

		T2_EX = 0;	    // bring logical clock low
		*left = *left<<1;
		*left |= P0_0;      // read the next bit
		*right = *right<<1;
		*right |= P0_1;     // read the next bit
		
		T2_EX = 1;          // bring logical clock high
	}

}

// Look-up table to convert the combination of bytes from the left and right 8-directional pads 
// to character, when the Shift button is OFF
code char LookUp[8][8]={{0x61,0x62,0x63,0x64,0x65,0x66,0x67,0x68},
				   {0x69,0x6A,0x6B,0x6C,0x6D,0x6E,0x6F,0x70},
				   {0x71,0x72,0x73,0x74,0x75,0x76,0x77,0x78},
				   {0x79,0x7A,0x39,0x30,0x2D,0x3D,0x3B,0x27},
				   {0x31,0x32,0x33,0x34,0x35,0x36,0x37,0x38},
				   {0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF},
				   {0xFF,0xFF,0x20,0xFF,0x10,0xFF,0x08,0xFF},
				   {0x60,0x2C,0x2E,0x2F,0x5D,0x5B,0x5C,0xFF}};

// Look-up table to convert the combination of bytes from the left and right 8-directional pads 
// to character, when the Shift button is ON
code char ShftLookUp[8][8]={{0x41,0x42,0x43,0x44,0x45,0x46,0x47,0x48},
					   {0x49,0x4A,0x4B,0x4C,0x4D,0x4E,0x4F,0x50},
					   {0x51,0x52,0x53,0x54,0x55,0x56,0x57,0x58},
					   {0x59,0x5A,0x28,0x29,0x5F,0x2B,0x3A,0x22},
					   {0x21,0x40,0x23,0x24,0x25,0x5E,0x26,0x2A},
					   {0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF},
					   {0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF},
					   {0x7E,0x3C,0x3E,0x3F,0x7D,0x7B,0x7C,0xFF}};

// Convert the combination of bytes from the left and right 8-directional pads to character
char decode(char left, char right){
	char rtnVal = 0;         // return value
	char dirLeft, dirRight;  // intermediate values 
	char shift = 0;          // state of the shift button
	
	shift = ~left & 0x80;    // get the status of the Shift
	left = left & 0x0F;      // cut off unneeded bits
	right = right & 0x0F;    // cut off unneeded bits

	// convert bytes from 4021-Ic into intermediate values
	switch (left){
	case 7:
		dirLeft = 2;
		break;
	case 6:
		dirLeft = 3;
		break;
	case 14:
		dirLeft = 4;
		break;
	case 10:
		dirLeft = 5;
		break;
	case 11:
		dirLeft = 6;
		break;
	case 9:
		dirLeft = 7;
		break;
	case 13:
		dirLeft = 0;
		break;
	case 5:
		dirLeft = 1;
		break;
	default:
		dirLeft = 8;
	}

	switch (right){
	case 7:
		dirRight = 2;
		break;
	case 6:
		dirRight = 3;
		break;
	case 14:
		dirRight = 4;
		break;
	case 10:
		dirRight = 5;
		break;
	case 11:
		dirRight = 6;
		break;
	case 9:
		dirRight = 7;
		break;
	case 13:
		dirRight = 0;
		break;
	case 5:
		dirRight = 1;
		break;
	default:
		dirRight = 8;
	}
	
	// sanity check
	if (dirLeft > 7 || dirRight > 7) return 0;

	// get the char value out of look-up tables depending on if the Shift is on or off
	if (shift){
		rtnVal = ShftLookUp[dirLeft][dirRight];
	} else {
		rtnVal = LookUp[dirLeft][dirRight];
	}

	return rtnVal;
}


void main(){
	unsigned int	counter,	// Counts number of times with same input
			counter2,	// counts number of times
	char	left,			// input from left pad
		right,			// input from right pad
		oldOut,			// Ascii decode output
		newOut;			// new ascii value
	bit 	flag;

	// set up for serial communications
	SCON = 0x52; /* SCON */
	TMOD = 0x20; /* TMOD */
	TCON = 0x69; /* TCON */
	TH1 =  0x98; /* TH1 */ // setup serial port hdw to 19.2K Baud @32 MHz

	while (1){
		flag = (flag) ? 0:1;		
		P1_2 = flag;
		readPads(&left, &right);	// Get current values from left and right game pads
		newOut = decode(left, right);	// Translate values to ASCII
		if (newOut == oldOut){
			counter++;
			if (counter > THRESHOLD){  // Make sure the value is steady before changing it

				// Send output char to 8051's parallel port P2 to be able 
				// to connect it to GPIO port of a CerfBoard (other project)
				P2 = oldOut;

				// Output the character once and delay 
				// before autorepeating if user keeps holding the keys
				counter2++;
				if(counter2 == 1 || counter2 >= 4){ 
					SBUF = oldOut; 
				}
			}
		}else{      // the different character has been input
			P2 = 0;
			counter = 0;
			counter2 = 0;
			oldOut = newOut;
		}
	}
}