Simple down to earth frequency counter.

#define F_CPU 8000000UL
#include <avr/interrupt.h>
#define USART_BAUDRATE 9600
#define BAUD_PRESCALE (((F_CPU / (USART_BAUDRATE * 16UL))) - 1)
#include <stdlib.h>
#include<avr/io.h>
#include<util/delay.h>
#define rs PB0   
#define en PB2


short val,val1,i;
unsigned int presc;
char a[10];
char ff[5] = {'F','r','e','q',':'};
void lcddata(char dataout);
void lcdcmd(char cmdout);
void dis_data(char data_value);
void dis_cmd(char cmd_value);
void lcd_init()    ;

int main()
{
    DDRD = 0x02;
    DDRB =0xff;
    //counter1 initialization
    TIMSK |= 1<<TICIE1;
    //TCCR1B |=
    TCCR1B |=(1<<ICES1)|(1 << CS12) | (1 << CS11) | (1 << CS10);
    //counter 0 initialization
    TIMSK |= (1<<TOIE0);
    TCCR0 = (1<<CS02) | (1<<CS00);
    _delay_ms(50);        // delay of 50 mili seconds
    lcd_init();    // fuction for intialize
    sei();
    while(1)
    {
/*    switch (presc)
    {
     case 1024:
         TCCR0 = (1<<CS02) | (1<<CS00);
     case 256:
        TCCR0 = (1<<CS02);
    case 64:
        TCCR0 = (1<<CS01) | (1<<CS00);
    case 8:
        TCCR0 = (1<<CS01) ;
    case 1:
        TCCR0 = (1<<CS00);
    default :
        TCCR0 = (1<<CS02) | (1<<CS00);

    }*/
     }

    return 0;
}


ISR(TIMER0_OVF_vect)
{
        val =TCNT1;
        TCNT1=0x00;
        TCNT0=0X00;
        TIFR =0x00;
        val =(val/19.912)*100;
        itoa(val,a,10);
        for(i=0;i<=5;i++)
        {
     dis_data(ff[i]);
        }
        for(i=0;i<=10;i++)
        {
     dis_data(a[i]);
        }
        _delay_ms(100);
   
}
void lcd_init()    // fuction for intialize
{
    dis_cmd(0x83);
    dis_cmd(0x02);        // to initialize LCD in 4-bit mode.
    dis_cmd(0x28);        //to initialize LCD in 2 lines, 5X7 dots and 4bit mode.
    dis_cmd(0x0C);
    dis_cmd(0x06);
    dis_cmd(0x83);
    dis_cmd(0x01);
}

void dis_cmd(char cmd_value)
{
    char cmd_value1;
   
    cmd_value1 = cmd_value & 0xF0;        //mask lower nibble because PA4-PA7 pins are used.
    lcdcmd(cmd_value1);            // send to LCD

    cmd_value1 = ((cmd_value<<4) & 0xF0);    //shift 4-bit and mask
    lcdcmd(cmd_value1);            // send to LCD
}                       


void dis_data(char data_value)
{
    char data_value1;
   
    data_value1=data_value&0xF0;
    lcddata(data_value1);

    data_value1=((data_value<<4)&0xF0);
    lcddata(data_value1);
}

void lcdcmd(char cmdout)
{
    PORTB=cmdout;
    PORTB&=~(1<<rs);
    PORTB|=(1<<en);
    _delay_ms(1);
    PORTB&=~(1<<en);
}

void lcddata(char dataout)
{
    PORTB=dataout;
    PORTB|=(1<<rs);
    PORTB|=(1<<en);
    _delay_ms(1);
    PORTB&=~(1<<en);
}