#include <avr/io.h>

int g_minutes = 0;
int g_hour = 0;
int g_seconds = 0;

void incSeconds()
{
   g_seconds++;
   if( g_seconds == 60 )
   {
      g_seconds = 0;
      g_minutes++;
      if( g_minutes == 60 )
      {
         g_minutes = 0;
         g_hour++;
         g_hour %= 24;
       }
   }
}

void displayTime()
{
   int digits[4];
   digits[1] = g_hour % 10;
   digits[0] = ( g_hour % 100 - digits[1] ) / 10;
   digits[3] = g_minutes % 10;
   digits[2] = ( g_minutes % 100 - digits[3] ) / 10;
   digits[0] = 1;
   digits[1] = 5;
   digits[2] = 8;
   digits[3] = 9;
   PORTB = digits[0];
   PORTC = 1 << 0;
   PORTC = 0;
   PORTB = digits[1];
   PORTC = 1 << 1;
   PORTC = 0;
   PORTB = digits[2];
   PORTC = 1 << 2;
   PORTC = 0;
   PORTB = digits[3];
   PORTC = 1 << 3;
   PORTC = 0;
}

int main(void) {
   DDRB = 0xFF;
   DDRC = 0xFF;

   PORTB = 0;
   PORTC = 0;

   while( 1 )
   {
      incSeconds();
      displayTime();
   }
   return 0;
}