UART using timers in atmega32

ISR (TIMER1_COMPA_vect)    // Timer1 ISR
    {
   if(PINA!=0x1f)                  //this is a condition where if any button pressed(out of 5 buttons i am using) will be detected
      {
	 val=PINA;                  
	 button(val);              //passing PINA value  
      }	
	  if((UCSRA&(1<<RXC)))                 //if recevied anytime
	  {
	   received_data=UDR;                  //store the value received
	   decide_func(received_data);      //Passing received value.
	  }
    }

   TCCR1B |= (1 << WGM12)|(1 << CS11)|(1 << CS10);
   TCNT1 = 0;
   OCR1A = 2499;                                                           //I just set this value because it works fine not calculated(please help me here how to 
                                                                                    //determine the value to be set in here.
   TIMSK |= (1 << OCIE1A);

 while(!(UCSRA&(1<<UDRE)));
	  UDR=0b00000101;