#define F_CPU 16000000

#include <avr/io.h> //standard AVR header
#include <util/delay.h> //delay header

#define KEY_PRT PORTK //keyboard PORT
#define KEY_DDR DDRK //keyboard DDR
#define KEY_PIN PINK //keyboard PIN


void usart_init (void) {
  UCSR0B = (1 << TXEN0);    // TX enabled

  // Asynchronous USART, no parity, 1-bit stop, 8-bit data
  UCSR0C = (1 << UCSZ01) | (1 << UCSZ00);
  
  // (Fosc / 16 (baud rate)) – 1
  // (16e6 / (16*9600)) – 1 = 103.17 ~ 103 = 0x67
  UBRR0L = 0x67; 
}

void usart_send (unsigned char ch) {
  while (!(UCSR0A & (1 << UDRE0)));
  UDR0 = ch;
}

unsigned char keypad[4][4] = {
    '1','2','3','A',
    '4','5','6','B',
    '7','8','9','C',
    '*','0','#','D'
};

int main(void) {

    unsigned char colloc, rowloc;
    
    //keyboard routine. This sends the ASCII
    //code for pressed key to port c
    
    DDRB = 0xFF;
    KEY_DDR = 0xF0; //
    KEY_PRT = 0xFF;

    usart_init();

    while (1) //repeat forever
    {
        do {
            KEY_PRT &= 0x0F; //ground all rows at once
            colloc = (KEY_PIN & 0x0F); //read the columns
        } while (colloc != 0x0F); //check until all keys released
        do {
            do {
                _delay_ms(20); //call delay
                colloc = (KEY_PIN & 0x0F); //see if any key is pressed
            } while (colloc == 0x0F); //keep checking for key press
            
            _delay_ms(20); //call delay for debounce
            colloc = (KEY_PIN & 0x0F); //read columns

        } while (colloc == 0x0F); //wait for key press

        while (1) {
            KEY_PRT = 0xEF; //ground row 0
            colloc = (KEY_PIN & 0x0F); //read the columns
            if (colloc != 0x0F) //column detected
            {
                rowloc = 0; //save row location
                break; //exit while loop
            }

            KEY_PRT = 0xDF; //ground row 1
            colloc = (KEY_PIN & 0x0F); //read the columns
            if (colloc != 0x0F) //column detected
            {
                rowloc = 1; //save row location
                break; //exit while loop
            }
            
            KEY_PRT = 0xBF; //ground row 2
            colloc = (KEY_PIN & 0x0F); //read the columns
            if (colloc != 0x0F) //column detected
            {
                rowloc = 2; //save row location
                break; //exit while loop
            }
            
            KEY_PRT = 0x7F; //ground row 3
            colloc = (KEY_PIN & 0x0F); //read the columns
            rowloc = 3; //save row location
            break; //exit while loop
        }

        //check column and send result to Port D
        if (colloc == 0x0E) {
            // PORTB = (keypad[rowloc][0]);
            usart_send(keypad[rowloc][0]);
        } else if (colloc == 0x0D) {
            // PORTB = (keypad[rowloc][1]);
            usart_send(keypad[rowloc][1]);
        } else if (colloc == 0x0B) {
            // PORTB = (keypad[rowloc][2]);
            usart_send(keypad[rowloc][2]);
        }
        else {
            // PORTB = (keypad[rowloc][3]);
            usart_send(keypad[rowloc][3]);
        }
    }
    
    return 0;
}