#define F_CPU 20000000

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

//note division factor of 8 by default in CLKPS register

//input is 0...DDxn &= ~(1 << pin)
//output is 1...DDxn |= (1 << pin)
//high/pur is 1...PORTx |= (1 << pin) (pullup resister activated if input, driven high if output)
//low is 0...PORTx &= ~(1 << pin)
//see page 55 of attiny manual

#define LED PA7
#define BUTTON PB2

void delay_ms(uint16_t millis) {
 while ( millis ) {
 _delay_ms(1);
 millis--;
 }
}

int main(void) {

 CLKPR = (1 << CLKPCE); //set clkps register to not divide clock speed by 8
 CLKPR = (0 << CLKPS3) | (0 << CLKPS2) | (0 << CLKPS1) | (0 << CLKPS0);

 DDRA |= (1 << LED); // PA7 output
 DDRB &= ~(1 << BUTTON); //PB2 input
 PORTB |= (1 << BUTTON); //PB2 is pulled high
 
 while(1) {
	 
	if(bit_is_clear(PINB, BUTTON)) {
	PORTA |= (1 << LED);
	} else {
	PORTA &= ~(1 << LED);
	}
   
 }
  
 return 0;
}