#define F_CPU 8000000UL

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

uint8_t i; // temp variable
uint8_t al; // ADC low
uint8_t ah; // ADC high

volatile uint8_t timer = 0;

uint8_t checksum = 255;

int main()
{
cli();
    UBRR0H = 0;
    UBRR0L = 1;
    UCSR0B = 0b00001000;
    ADMUX = 0b01000111; // Select A7
    ADCSRA = 0b11000110; // Enable ADC, single conversion, f/64 = 125kHz

    TCCR2A = 0b010; // TOP = OCRA
    TCCR2B = 0b100; // Div 32
    OCR2A = 156;  // 138 = 905Hz interrupts
    TCNT2 = 0;
    TIMSK2 = 0b010; // OCIEA interrupt

sei();

    i = 0;

    UDR0 = 0x00; // Send a NULL to start

    for(;;) {

        ADMUX = 0b01000110; // A6
        ADCSRA = 0b11000110; // Enable ADC, single conversion, f/64 = 125kHz
        while(!(UCSR0A & 0b00100000)); // Wait for buffer to be empty
        UDR0 = ah; // High byte first
        while(!(UCSR0A & 0b00100000)); // Wait for buffer to be empty
        UDR0 = al; // High byte first
        while(ADCSRA & 0b01000000); // Wait for conversion to finish (should be done)
        al = ADCL;
        ah = ADCH;
        checksum -= al;
        checksum -= ah;

        ADMUX = 0b01000101; // A5
        ADCSRA = 0b11000110; // Enable ADC, single conversion, f/64 = 125kHz
        while(!(UCSR0A & 0b00100000)); // Wait for buffer to be empty
        UDR0 = ah; // High byte first
        while(!(UCSR0A & 0b00100000)); // Wait for buffer to be empty
        UDR0 = al; // High byte first
        while(ADCSRA & 0b01000000); // Wait for conversion to finish (should be done)
        al = ADCL;
        ah = ADCH;
                checksum -= al;
        checksum -= ah;


        ADMUX = 0b01000000; // A0
        ADCSRA = 0b11000110; // Enable ADC, single conversion, f/64 = 125kHz
        while(!(UCSR0A & 0b00100000)); // Wait for buffer to be empty
        UDR0 = ah; // High byte first
        while(!(UCSR0A & 0b00100000)); // Wait for buffer to be empty
        UDR0 = al; // High byte first
        while(ADCSRA & 0b01000000); // Wait for conversion to finish (should be done)
        al = ADCL;
        ah = ADCH;
        checksum -= al;
        checksum -= ah;


        ADMUX = 0b01000001; // A1
        ADCSRA = 0b11000110; // Enable ADC, single conversion, f/64 = 125kHz
        while(!(UCSR0A & 0b00100000)); // Wait for buffer to be empty
        UDR0 = ah; // High byte first
        while(!(UCSR0A & 0b00100000)); // Wait for buffer to be empty
        UDR0 = al; // High byte first
        while(ADCSRA & 0b01000000); // Wait for conversion to finish (should be done)
        al = ADCL;
        ah = ADCH;
        checksum -= al;
        checksum -= ah;

        ADMUX = 0b01000010; // A2
        ADCSRA = 0b11000110; // Enable ADC, single conversion, f/64 = 125kHz
        while(!(UCSR0A & 0b00100000)); // Wait for buffer to be empty
        UDR0 = ah; // High byte first
        while(!(UCSR0A & 0b00100000)); // Wait for buffer to be empty
        UDR0 = al; // High byte first
        while(ADCSRA & 0b01000000); // Wait for conversion to finish (should be done)
        al = ADCL;
        ah = ADCH;
        checksum -= al;
        checksum -= ah;


        while(!(UCSR0A & 0b00100000)); // Wait for buffer to be empty
        UDR0 = ah; // High byte first
        while(!(UCSR0A & 0b00100000)); // Wait for buffer to be empty
        UDR0 = al; // High byte first

        while(!(UCSR0A & 0b00100000)); // Wait for buffer to be empty
        UDR0 = checksum; // High byte first
        checksum = 255;

        while(timer == 0); // Hold here to enforce 900Hz reading rate
        timer = 0;

        ADMUX = 0b01000111; // A7
        ADCSRA = 0b11000110; // Enable ADC, single conversion, f/64 = 125kHz
        while(!(UCSR0A & 0b00100000)); // Wait for buffer to be empty
        UDR0 = 0x00; // NULL start

        while(ADCSRA & 0b01000000); // Wait for conversion to finish (should be done)
        al = ADCL;
            ah = ADCH;
        checksum -= al;
        checksum -= ah;



    }
    return 1;
}

ISR(TIMER2_COMPA_vect)
{
    timer=1;
}