/* Alcohol Unit Counter - see http://www.technoblogy.com/show?2AUF

   David Johnson-Davies - www.technoblogy.com - 26th August 2018
   ATtiny84 @ 8 MHz (external crystal; BOD disabled)
   
   CC BY 4.0
   Licensed under a Creative Commons Attribution 4.0 International license: 
   http://creativecommons.org/licenses/by/4.0/
*/

#include <avr/sleep.h>
#include <avr/power.h>

// Seven-segment definitions
const int charArrayLen = 14;
char charArray[] = {
//  ABCDEFG  Segments
  0b1111110, // 0
  0b0110000, // 1
  0b1101101, // 2
  0b1111001, // 3
  0b0110011, // 4
  0b1011011, // 5
  0b1011111, // 6
  0b1110000, // 7
  0b1111111, // 8
  0b1111011, // 9
  0b0000000, // 10  Space
  0b0000001, // 11  '-'
  0b0001000, // 12  '_'
  0b1000000  // 13  '^'
};

const int Blank = 10;
const int Minus = 11;
const int Under = 12;
const int Over = 13;
const int ndigits = 2;
const int Units = 2;                      // Allowed units per day
const int Day = 1350;                     // Number of ticks in a day
const int Delay = 500;                    // Number of display cycles before display blanks
const int Max = 40;
const int Min = -10;
const int Start = 675;                    // Number of ticks before clock first updates 


volatile char Buffer[] = {2, 2};
char digit = 0;

volatile int Counter;                     // Units counter
volatile int Ticks = Start;               // Time counter
volatile int Timeout = 0;                 // Display timeout; 0 = off

// Pin assignments

char Digits[] = {PORTA1, PORTA7};         // Port A pins
const int Button = PIN_B2;

// Display multiplexer **********************************************

void DisplayNextDigit () {
  digit = digit ^ 1;                      // Toggle between 0 and 1
  char segs = charArray[Buffer[digit]];
  PORTA = 0;                              // All low
  DDRA = 0;                               // All inputs
  DDRA = segs & 0x7F;                     // Set display segments
  DDRA = DDRA | 1<<Digits[digit];         // Make it an output
  PORTA = PORTA | 1<<Digits[digit];       // Make it high
}

// Display a two-digit number
void Display (int n) {
  int units = n % 10;
  int tens = n / 10;
  int temp0 = tens;
  int temp1 = abs(units);
  if (tens < 0) temp0 = temp1 = Under;
  else if (tens > 3) temp0 = temp1 = Over;
  else if ((tens == 0) && (units >= 0)) temp0 = Blank;
  else if ((tens == 0) && (units < 0)) temp0 = Minus;
  Buffer[0] = temp0;
  Buffer[1] = temp1;
}

// Timer/Counter0 interrupt - multiplexes display - 125Hz
ISR(TIM0_COMPA_vect) {
  DisplayNextDigit();
  Timeout--;
  if (Timeout != 0) return;
  TIMSK0 = 0<<OCIE0A;                     // Disable compare match interrupt
  DDRA = 0;                               // Blank display - all inputs
  PORTA = 0xFF;                           // All pullups on
}

// Timer/Counter1 interrupt - called every 64 secs
ISR(TIM1_COMPA_vect) {
  Ticks--;
  if (Ticks != 0) return;
  Ticks = Day;
  Counter = max(Counter - Units, Min);
}

// Pushbutton **********************************************
  
// Pushbutton interrupt - turns on the display
ISR(INT0_vect) {
  int val, lastval=0, count = 0;
  do {
    val = PINB & 1<<PINB2;
    if (val == lastval) count++;
    else { lastval = val; count = 0; }
  } while (count < 8);
  if (val != 0) return;
  // Only increment if display already on and button down
  if (Timeout != 0) Counter = min(Counter + 1, Max);
  Display(Counter);
  Timeout = Delay;                        // 4 seconds
  TIMSK0 = 1<<OCIE0A;                     // Enable compare match interrupt
  GIFR = 1<<INTF0;                        // Clear interrupt from bounce
}

// Setup **********************************************

void setup () {
  // Wait before slowing down clock so we can use In-System Programming
  delay(2000);
  //
  // Slow down clock by factor of 256 to save power
  CLKPR = 1<<CLKPCE;
  CLKPR = 8<<CLKPS0;                      // Clock to 31250 Hz
  //
  // Set up button
  PORTB = 1<<PORTB2;                      // Input pullup
  MCUCR = MCUCR | 2<<ISC00;               // Interrupt on falling edge
  GIMSK = 1<<INT0;                        // Enable INT0 interrupt
  //
  // Set up Timer/Counter1 to keep the time
  TCCR1A = 0<<WGM10;                      // CTC mode
  TCCR1B = 1<<WGM12 | 3<<CS10;            // Divide by 64
  OCR1A = 31249;                          // Compare match at 1/64 Hz
  TIMSK1 = 1<<OCIE1A;                     // Enable compare match interrupt
  //
  // Set up Timer/Counter0 to multiplex the display
  TCCR0A = 2<<WGM00;                      // CTC mode; count up to OCR0A
  TCCR0B = 0<<WGM02 | 1<<CS00;            // Divide by 1
  OCR0A = 249;                            // Compare match at 125Hz
  TIMSK0 = 0;                             // Initially disable interrupts
  //
  ADCSRA &= ~(1<<ADEN);                   // Disable ADC to save power
  PRR = 1<<PRUSI | 1<<PRADC;              // Turn off clocks to USI & ADC to save power
  set_sleep_mode(SLEEP_MODE_IDLE);
}

void loop () {
  sleep_enable();
  sleep_cpu();                            // Go back to sleep after each interrupt
}