有個測試 5V電源PWM頻率的程序看不太懂，還請高人指點��！

void time0_init(void)
{
   TCCR0 = 0x00; 
   TCNT0 = 0x00;
   TIMSK|=(1<<TOIE0);//TIMER0 溢出中斷使能
}


ISR(TIMER0_OVF_vect)                      //TIMER0 溢出中斷
{
  over_falg++;
 } 

 

 l  ast_time=0;
    over_falg1=0;
    over_falg =0;
    sei();
    i=0;
    TCNT0=0x00;
    DDRA=0X00;
              
          do
    {
      i++;
         if (i>=65000)
         goto overtime;
     }
       while ((PINA & 0X08)==0X08);
            i=0;
       do
      {
       i++;
          if (i>=65000)
          goto overtime;
      }
           while ((PINA & 0X08) ==0X00);
      i=0;
      TCCR0|=(1<<CS01)|(1<<CS00);
          do
     {   i++;
            if (i>=65000)
            goto overtime;   
      }
        while ((PINA & 0X08)==0X08);
          i=0; 
     do
      {
           i++;
              if (i>=65000)
              goto overtime;

       }
        while ((PINA & 0X08 )==0X00);
     over_falg1=over_falg;
     last_time=TCNT0;
               overtime:
           send(over_falg1);
                 send(last_time);
        TCCR0=0x00;
                 TCNT0=0X00;