/*
LCD Pin	LCD Function	Arduino Pin	AVR Pin	Register
--------------------------------------------------
7	      D0	          D2	        PD2	    PORTD
8	      D1	          D3	        PD3	    PORTD
9	      D2	          D4	        PD4	    PORTD
10	    D3	          D5	        PD5	    PORTD
11	    D4	          D6	        PD6	    PORTD
12	    D5	          D7	        PD7	    PORTD
13	    D6	          D8	        PB0	    PORTB
14	    D7	          D9	        PB1	    PORTB
-------------------------------------------------
*/

#include <avr/io.h>
#include <util/delay.h>

// LCD control pins
#define RS PB4
#define EN PB3

void lcdPulseEnable() 
{
  PORTB |= (1 << EN);
  _delay_us(1);
  PORTB &= ~(1 << EN);
  _delay_us(100);
}

void lcdSendByte(uint8_t byte, uint8_t isData) 
{
  if (isData)
    PORTB |= (1 << RS);  // Data mode
  else
    PORTB &= ~(1 << RS); // Command mode

  // Clear previous data bits on PD2–PD7 and PB0–PB1
  PORTD &= 0b00000011; // Clear PD2–PD7 (D0–D5)
  PORTB &= 0b11111100; // Clear PB0–PB1 (D6–D7)

  // Assign bits to correct pins
  // D0–D5 → PD2–PD7
  PORTD |= (byte << 2) & 0b11111100;

  // D6–D7 → PB0–PB1
  PORTB |= (byte >> 6) & 0b00000011;

  lcdPulseEnable();
  _delay_ms(2);
}

void lcdCommand(uint8_t cmd) 
{
  lcdSendByte(cmd, 0);
}

void lcdData(uint8_t data) 
{
  lcdSendByte(data, 1);
}

void lcdInit() 
{
  _delay_ms(20);
  lcdCommand(0x38); // 8-bit, 2-line
  lcdCommand(0x0C); // Display ON, Cursor OFF
  lcdCommand(0x06); // Auto-increment
  lcdCommand(0x01); // Clear display
  _delay_ms(2);
}

void lcdPrint(const char *str) 
{
  while (*str) 
  {
    lcdData(*str++);
  }
}

void setup() 
{
  // RS, EN, D6, D7 (PB4, PB3, PB0, PB1)
  DDRB |= (1 << RS) | (1 << EN) | (1 << PB0) | (1 << PB1);

  // D0–D5 (PD2–PD7)
  DDRD |= 0b11111100;

  lcdInit();
  lcdPrint("Bare-Metal LCD");
}

void loop() 
{
  // Do nothing
}

/*
//bare metal code using digitalWrite, pinMode functions
#define RS 12
#define EN 11

// D0–D7 connected to D2–D9
const int dataPins[8] = {2, 3, 4, 5, 6, 7, 8, 9};

void pulseEnable() {
  digitalWrite(EN, HIGH);
  delayMicroseconds(1);
  digitalWrite(EN, LOW);
  delayMicroseconds(100); // allow LCD to process
}

void sendCommand(uint8_t cmd) {
  digitalWrite(RS, LOW); // command mode

  // Send each bit to data lines
  for (int i = 0; i < 8; i++) {
    digitalWrite(dataPins[i], (cmd >> i) & 0x01);
  }

  pulseEnable();
  delay(2);
}

void sendData(uint8_t data) {
  digitalWrite(RS, HIGH); // data mode

  for (int i = 0; i < 8; i++) {
    digitalWrite(dataPins[i], (data >> i) & 0x01);
  }

  pulseEnable();
  delay(2);
}

void lcdInit() {
  delay(20);               // LCD power-on delay
  sendCommand(0x38);       // 8-bit, 2 line, 5x8 font
  sendCommand(0x0C);       // Display ON, Cursor OFF
  sendCommand(0x06);       // Auto increment cursor
  sendCommand(0x01);       // Clear display
  delay(2);
}

void lcdPrint(const char *str) {
  while (*str) {
    sendData(*str++);
  }
}

void setup() {
  pinMode(RS, OUTPUT);
  pinMode(EN, OUTPUT);
  for (int i = 0; i < 8; i++) {
    pinMode(dataPins[i], OUTPUT);
  }

  lcdInit();                      // Initialize LCD
  lcdPrint("Hello, Bare Metal!"); // Display message
}

void loop() {
  // Nothing to do
}
*/