인터럽트를 쓰지 않았을 때 비효율 적인 연산이 일어남을 보여주는 소스

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


#define LED 5
#define output_low(port,pin) port &= ~(1<<pin)
#define output_high(port,pin) port |= (1<<pin)
#define set_input(portdir,pin) portdir &= ~(1<<pin)
#define set_output(portdir,pin) portdir |= (1<<pin)


#define FOSC 16000000
#define BAUD 9600
#define UBRR FOSC/16/BAUD-1

void init_USART0(unsigned int baud)
{
UBRR0 = baud; // Set Baudrate
UCSR0C = (3<<UCSZ00); // Character Size 8 bit
UCSR0B |= _BV(RXEN0) | _BV(TXEN0); // Receiver and Transmitter Enable
}


void setRXCIE_USART0()
{
UCSR0B |= _BV(RXCIE0);
}


unsigned char receive_1byte_USART0(void)
{
loop_until_bit_is_set(UCSR0A, RXC0);
return UDR0;
}


void transmit_1byte_USART0(unsigned char data)
{
loop_until_bit_is_set(UCSR0A, UDRE0);
UDR0 = data;
}



void transmit_str_USART0(char *str)
{
while (*str != 0) {
transmit_1byte_USART0(*str);
*str++;
}
}



void transmit_4digit_USART0(int num)
{
unsigned char temp;
int digit = 1000;


while (digit != 0) {
temp = num / digit;
transmit_1byte_USART0('0'+temp);
num -= (digit*temp);
digit /= 10;
}
}



int main()
{
set_output(DDRC, LED);
init_USART0(UBRR); // initialize USART0


while (1) {
if ('a' == receive_1byte_USART0()) {
transmit_str_USART0("Hello World!\r\n");
output_high(PORTC, LED);
_delay_ms(1000);

output_low(PORTC, LED);
_delay_ms(1000);


}
}


return 0;
}