/*
ATmega8, 48, 88, 168, 328

/Reset PC6|1   28|PC5
 row_1 PD0|2   27|PC4
 row_2 PD1|3   26|PC3 
 row_3 PD2|4   25|PC2 
 row_4 PD3|5   24|PC1 
 row_5 PD4|6   23|PC0 
       Vcc|7   22|Gnd
       Gnd|8   21|Aref
       PB6|9   20|AVcc
       PB7|10  19|PB5 SCK   Anode_1 
 row_6 PD5|11  18|PB4 MISO  Anode_2
 row_7 PD6|12  17|PB3 MOSI  Anode_3
 row_8 PD7|13  16|PB2       Anode_4
       PB0|14  15|PB1       Anode_4
*/

#define F_CPU 1000000UL
#include <avr/io.h>
#include <util/delay.h>
#include <avr/interrupt.h>

uint8_t font[10][6]=
{
    {0x3E, 0x41, 0x49, 0x41, 0x3E, 0x00}, // 0x30 0
    {0x00, 0x42, 0x7F, 0x40, 0x00, 0x00}, // 0x31 1
    {0x42, 0x61, 0x51, 0x49, 0x46, 0x00}, // 0x32 2
    {0x21, 0x41, 0x45, 0x4B, 0x31, 0x00}, // 0x33 3
    {0x18, 0x14, 0x12, 0x7F, 0x10, 0x00}, // 0x34 4
    {0x27, 0x45, 0x45, 0x45, 0x39, 0x00}, // 0x35 5
    {0x3C, 0x4A, 0x49, 0x49, 0x30, 0x00}, // 0x36 6
    {0x01, 0x71, 0x09, 0x05, 0x03, 0x00}, // 0x37 7
    {0x36, 0x49, 0x49, 0x49, 0x36, 0x00}, // 0x38 8
    {0x06, 0x49, 0x49, 0x29, 0x1E, 0x00}, // 0x39 9
};

volatile uint8_t framebuffer[5];

ISR(TIMER0_OVF_vect)
{
  static uint8_t digit;
  PORTB &= 0b11000001;             // clear all columns
  PORTB |= (0b00000010 << digit);  // set current column
  PORTD = framebuffer[digit];      // update rows
  digit++;
  digit = digit % 5;
}

void init(void)
{
  DDRD = ?;   // rows
  DDRB = ?;   // columns
  
  // we start with 
  //   normal operation
  //   clk/1024 prescaler (about 1kHz)  
  //   interrupt on Timer 0 overflow
  
  TCCR0A = (0 << COM0A1) | (0 << COM0A0) | (0 << COM0B1) | (0 << COM0B0)
         | (? << WGM01)  | (? << WGM00);   
  TCCR0B = (0 << WGM02) 
         | (? << CS02)   | (? << CS01)   | (? << CS00);
  TIMSK0 = (0 << OCIE0B) | (0 << OCIE0A) | (? << TOIE0); 
  
  // allow interrupts globally
  sei();     
}

int main(void)
{
  uint16_t count=0; 
  uint8_t  i;
  init();
  while(1)
  {
    for (i=0; i<5; i++)
    {
      framebuffer[i] = ~font[count][i];
    }
    count++;
    if (count >= 10)
    {
      count = 0;
    }
    _delay_ms(1000);
  }
}