ult

#define F_CPU 16000000UL
#define BAUD 9600
#define MYUBRR ((F_CPU/16/BAUD)-1)

#include <avr/io.h>
#include <avr/interrupt.h>
#include <util/delay.h>

volatile uint16_t time; // time before send
volatile uint16_t time_cap; // start time capt
volatile char buffer[3]; // store set of int value in char from time capture

void USART_Transmit(unsigned char data){
    while( !(UCSR0A & (1<<UDRE0)));
    UDR0 = data;
}
void USART_init(unsigned int ubrr){
    //set baud rate
    UBRR0H = (unsigned char)(ubrr>>8);
    UBRR0L = (unsigned char)ubrr;
    UCSR0A &= 0xFD;
    //Enable transmitter
    UCSR0B = (1<<TXEN0);
    // set frame format 8data 2 stopbit
    UCSR0C = (3<<UCSZ00);
}
void Send_trig(void){
    UDR0 = 0x00;
    PORTB |= 0xF0; //PB0 LOGIC '1'
    _delay_us(10);
    PORTB &= 0x00; //PB0 LOGIC '0'
}
int main(void) {
    TCNT1 = 0;
    USART_init(MYUBRR);
    TCCR1A |= 0x00;// set up timer register TCCR1A - Normal Mode
    TCCR1B |= 0x45;// set up timer register TCCR1B prescaler 1024 and Normal Mode
    DDRB = 0xF0; // set port B pin 4 5 6 7 as output and 0 1 2 3 as input
    TIMSK1 = 0x21; // set interrupt
    TCNT1 = 57000; // start number
    sei(); // open interrupt
    Send_trig();
    while(1){
        // idle loop add after if want another function
    }
}


ISR(TIMER1_OVF_vect){
    TCCR1B = 0x45; // reset interrupt to rise edge
    Send_trig();
    TCNT1 = 57000;
}

ISR(TIMER1_CAPT_vect){
    if(TCCR1B == (0x45)){
        time_cap = TCNT1;
        TCCR1B = 0x05;
    }else{
        TIMSK1 &= ~((1<<ICIE1)|(1<<TOIE1));
        time = TCNT1 - time_cap;
        time = ((time*1024*34600)/F_CPU)/2; // cal time to distance
        itoa(time, buffer, 10);
        for (int i=0; i<sizeof(buffer); i++)
            USART_Transmit(buffer[i]);
        USART_Transmit('c');
        USART_Transmit('m');
        USART_Transmit(0x0a);
        TCCR1B = 0x45;
        TIMSK1|=(1<<ICIE1)|(1<<TOIE1);
        sei();
    }
}