main.c

#include <avr/io.h>
#include <avr/interrupt.h>
#include <util/delay.h>
#include <util/delay_basic.h>
#include "macroes.h"

// LCD is wired to PORTB
// higher bits are data bits,
// lower are flags

#define LCD_PORT PORTB
#define LCDRS    PB0
#define LCDRW    PB1
#define LCDE     PB2
#define LCD4     PB3     
#define LCD5     PB4     
#define LCD6     PB5     
#define LCD7     PB6     

void _lcd_cmd(uint8_t delay, uint8_t cmd){
  LCD_PORT = cmd;
  _delay_loop_1(delay);
  LCD_PORT = 0;
}

#define lcd_cmd(delay, ...) _lcd_cmd(delay, bits(LCDE, ## __VA_ARGS__))

void lcd_init(void){
  _delay_ms(1000); // it should be >15ms, but just in case
  /// page 34, 4-bit interface initialization
  lcd_cmd(5, LCD5, LCD4);
  lcd_cmd(1, LCD5, LCD4);
  lcd_cmd(1, LCD5, LCD4);
  lcd_cmd(1, LCD5);
  lcd_cmd(1, LCD5);
  lcd_cmd(1, LCD7);
  lcd_cmd(1);
  lcd_cmd(1, LCD7);
  lcd_cmd(1);
  lcd_cmd(1, LCD4);
  lcd_cmd(1);
  lcd_cmd(1, LCD5, LCD4);
}

void lcd_write(unsigned char c){
  // LCDRS to write to data
  _lcd_cmd(1, _BV(LCDRS) | ((c >> 4) << 4)); // higher
  _lcd_cmd(1, _BV(LCDRS) | ((c & 0x0F) << 4)); // lower
}

/*
 **	Main Function
 */
int main(void)
{
  DDRB = 0xFF;

  lcd_init();

  while(1){
    lcd_write('a');
  }

  //	Finally, return 0
  return 0;
}