attiny servo

/*
    kkmonster cmmc   : internal clock 1 Mhz
 */
#include <avr/interrupt.h>
#include <util/delay.h>
#define servo_pin     0

volatile int servo = 100;

void setup() 
{
  pinMode(servo_pin, OUTPUT);
  TCCR0A |=(1<<WGM01);   //CTC mode, set OC0A on match //Clear Timer on Compare Match (Auto Reload)
  TIMSK |= (1<<OCIE0A);  //CTC Interrupt enable
  sei();                 // enble interrupt
}
void loop() 
{
  servo = ???
  ....
}
ISR(TIMER0_COMPA_vect)
{
  digitalWrite(servo_pin, HIGH);
  delay_us(50);       // calibation for 500us
  delay_us(servo);    // 200 for delay 1500us
  digitalWrite(servo_pin, LOW);
}
void delay_us(int temp)
{
  while(temp > 0)
  {
    _delay_us(1);
    temp--;
  }
}