/*
 TinyMixer.c - Copyright (c) 2014 Mark Moran
 Redistribution and use in source and binary forms, with or without
 modification, are permitted freely.
 Written for ATtiny13 running at 9.6MHz (internal RC), assumes RSTDSBL fuset is set (using PB5)
 */

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

#define REDIN       PB5
#define GREENIN     PB3
#define BLUEIN      PB4
#define REDOUT      PB2
#define GREENOUT    PB1
#define BLUEOUT     PB0
#define REDCH       0
#define GREENCH     3
#define BLUECH      2

// 0 = on all the time (port is low), 255 = off all time time (port is high)

volatile uint8_t count = 255, red = 255, green = 255, blue = 255;

ISR(TIM0_OVF_vect) {
    if (count==255) {
        count = 0;
        PORTB |= (1<<REDOUT) | (1<<GREENOUT) | (1<<BLUEOUT); // turn them all off
    }
    if (count == red)
        PORTB &= ~(1<<REDOUT);
    if (count == blue)
        PORTB &= ~(1<<BLUEOUT);
    if (count == green)
        PORTB &= ~(1<<GREENOUT);
    
    count++;
}

uint8_t readADC(uint8_t channel) {
    uint8_t i;
    uint16_t adcAvg;

    ADMUX = (ADMUX & 0b11111100) | channel;                 // set channel
    
    ADCSRA |= (1<<ADSC);                                    // start conversion
    loop_until_bit_is_clear(ADCSRA, ADSC);                  // wait until done
    adcAvg = ADCH;                                          // read top 8 bits so ADC can move on
    adcAvg = 0;                                             // throw away first value after changing channel
    
    // read 8 samples and return the average
    for (i = 0; i < 8; i++) {
        ADCSRA |= (1<<ADSC);
        loop_until_bit_is_clear(ADCSRA, ADSC);
        adcAvg += ADCH;
    }
	
    return (adcAvg / 8);
}

int main(void) {
    // setup inputs and outputs
    DDRB &= ~(1<<REDIN) | (1<<GREENIN) | (1<<BLUEIN);       // set 3 pins to input (default actually)
    DDRB |= (1<<REDOUT) | (1<<GREENOUT) | (1<<BLUEOUT);     // set 3 pins to output
    PORTB |= (1<<REDOUT) | (1<<GREENOUT) | (1<<BLUEOUT);    // pin high = LED off
    
    // initialize
    ADMUX = (1<<ADLAR);                                     // left justify result (we want top 8 bits)
    ADCSRA = (1<<ADEN) | (1<<ADPS1) | (1<<ADPS2);           // ADC on, prescaled by 64 (9.6MHz/64 = 150KHz)
                                                            // 8 bit only so could run faster than 200MHz
    
    // initialize timer
    TCCR0A = 0;                                             // not using any hardware PWM waveforms
    TCCR0B = (1<<CS00);                                     // use internal clock, no prescaling
    TIMSK0 = (1<<TOIE0);                                    // overflow interrupt enabled
    sei();                                                  // enable global interrupts
    
    while (1) {
        red = readADC(REDCH);
        green = readADC(GREENCH);
        blue = readADC(BLUECH);
        _delay_ms(2);
    }
}