/*
    Rudolph the red nosed reindeer breathing LED
    Atmel Studio 7 C Code for the PCBWay Christmas 2017 surprise kit
    (ATtiny85, 128KHz internal oscillator)
    Share and enjoy!
*/

// This must be at most 254
#define PWM_STEPS 64U

#define F_CPU 32000UL

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

void setup(void) {

    // Rudolph's nose is on PB0
    DDRB = 1;
    // Set clock prescaler 1:4
    // Unlock...
    CLKPR = (1 << CLKPCE);
    // Set
    CLKPR = 2;

}

void pwmCycle(uint8_t onTime) {

    uint8_t offTime = PWM_STEPS - onTime;
    while (offTime--) {
        PORTB &= ~1;
    }
    while (onTime--) {
        PORTB |= 1;
    }

}


int main(void)
{
    uint8_t x = 0;

    setup();

    while (1) {

        for (x = 0; x < PWM_STEPS; ++x) {
            pwmCycle(x);
        }

        for (--x; x < PWM_STEPS; --x) {
            pwmCycle(x);
        }

        _delay_ms(1000);

    }
}