/* Radio Clock

   David Johnson-Davies - www.technoblogy.com - 23rd July 2014
   
   CC BY 4.0
   Licensed under a Creative Commons Attribution 4.0 International license: 
   http://creativecommons.org/licenses/by/4.0/
*/

//Create global variables
volatile unsigned long milliseconds;
volatile int BitCount;
unsigned char BitBuffer;
boolean Parity;
boolean BitB;
char digit;
int RadioHours, RadioMins, Hours, Mins;

// Digit connections
const int ndigits = 4;
int Digits[] = {PIN_A4, PIN_B0, PIN_B1, PIN_A5};

// Segments must all go to port A
// This specifies which bit in port A goes to each segment
//                g  f  e  d  c  b  a  dp
int Segments[] = {1, 4, 6, 7, 3, 0, 2, 5};

const int RadioPin = PIN_B2;

// Display update
const int Space = 10;
const int Dash = 12;
char Buffer[4] = { Dash, Dash, Dash, Dash};
const int charArrayLen = 13;
char charArray[13] = {
//  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
  0b1001110, // 11  'C'
  0b0000001  // 12  '-'
};

// Count the population or number of '1's in x as binary
int pop(unsigned char x) {
  x = (x & 0x55) + ((x>>1) & 0x55);
  x = (x & 0x33) + ((x>>2) & 0x33);
  return (x & 0x0f) + (x>>4);
}

// Reorder the bits in charArray to match wiring
void ReorderBits() {
  int segs, newsegs;
  for (int i=0; i<charArrayLen; i++) {
    segs = charArray[i];
    newsegs = 0;
    for (int i=0; i<8; i++) {
      newsegs = newsegs | ((segs & 1)<<Segments[i]);
      segs = segs >> 1;
    }
    charArray[i]=newsegs;
  }  
}

// Display update routine - Gets called every 2 msec
void DisplayNextDigit() {
  int Segs, Char;
  // Turn display off
  pinMode(Digits[digit], INPUT);
  digit = (digit+1) % ndigits;
  Char = min(Buffer[digit],charArrayLen-1);
  Segs = charArray[Char & 0x7F];
  // Display colon?
  if ((Char & 0x80) && (digit==3)) {
    pinMode(Digits[2], OUTPUT);
    digitalWrite(Digits[2], LOW);
  }
  // Equalise brightness
  OCR0B = (pop(Segs) + 4) * 16; // Max 198
  DDRA = 0;     // All inputs
  PORTA = Segs ^ 0xFF; // 1 = high
  DDRA = Segs;  // 1 = output
}

// Timer 0 interrupt A - turns on display
ISR(TIM0_COMPA_vect) {
  pinMode(Digits[digit], OUTPUT);
  digitalWrite(Digits[digit], HIGH);
}

// Timer 0 interrupt B - turns off and sets up display
ISR(TIM0_COMPB_vect) {
  DisplayNextDigit();
  milliseconds += 2;
  Average();
}

// My millisecond timer
unsigned long MyMillis() {
  unsigned long m;
  uint8_t oldSREG = SREG;
  cli();
  m = milliseconds;
  SREG = oldSREG;
  return m;
}

// My millisecond delay routine
void MyDelay(unsigned long ms) {
  unsigned long Start;
  Start = MyMillis();
  while ((MyMillis() - Start) < ms);
}

void setup() {
  ReorderBits();
  // Set up Timer0 to multiplex the display
  TCCR0A = 3<<WGM00; // Fast PWM, 0 to OCRA
  TCCR0B = 1<<WGM02 | 2<<CS00; // clock/8
  OCR0A = 249; // CTC mode at 500Hz
  TIMSK0 = 1<<OCIE0A | 1<<OCIE0B; // Enable interrupts
}

// Buffers last 8 states of radio output (16msec)
void Average () {
  boolean Bit = digitalRead(RadioPin);
  BitCount = BitCount - ((BitBuffer & 0x80) >> 7) + Bit;
  BitBuffer = (BitBuffer<<1) | Bit;
}

// Returns true if averaged radio input is high
boolean Radio() {
  boolean b;
  uint8_t oldSREG = SREG;
  cli();
  b = BitCount >= 4;
  SREG = oldSREG;
  return b;
}

// Wait for next carrier off pulse (HIGH) and time it
int HighPulse() {
  unsigned long Start;
  while (!Radio()); // Low - carrier on
  Start = MyMillis();
  while (Radio()); // High - carrier off
  return MyMillis() - Start;
}

// Reads a bit from the timecode; assumes you started in inter-bit gap
boolean GetBit() {
  boolean result;
  while (!Radio());
  MyDelay(200);   // End of bit A
  result = (Radio());
  Parity = Parity ^ result;
  MyDelay(100);   // Middle of bit B
  BitB = BitB + (Radio());
  MyDelay(100);   // Get into gap
  return result;
}

void loop() {
  int bitbs, timeparity, LastHours, LastMins;
  // Wait for minute marker
  while (HighPulse() < 450);
  // Skip seconds 1 to 38
  for (int i=1; i<=38; i++) GetBit();
  // Read time
  LastHours = RadioHours;
  LastMins = RadioMins;
  Parity = 0;
  BitB = 0;
  int TenHours = GetBit() * 2 + GetBit();
  int UnitHours = GetBit() * 8 + GetBit() * 4 + GetBit() * 2 + GetBit();
  RadioHours = TenHours*10 + UnitHours;
  int TenMins = GetBit() * 4 + GetBit() * 2 + GetBit();
  int UnitMins = GetBit() * 8 + GetBit() * 4 + GetBit() * 2 + GetBit();
  RadioMins = TenMins*10 + UnitMins;
  timeparity = Parity;
  bitbs = BitB; // Should be zero
  // Skip next 5 bits
  for (int i=1; i<=5; i++) GetBit();
  BitB = 0;  
  GetBit(); // Parity
  boolean TimeValid = (bitbs == 0) && (BitB != timeparity) &&
    (RadioHours-LastHours==0) && (RadioMins-LastMins==1);
  if (TimeValid) {
    Hours = RadioHours;
    Mins = RadioMins;
  } else {
    Mins = Mins + 1;
    Hours = (Hours + Mins/60) % 24;
    Mins = Mins % 60;
  }
  // Display time in 12-hour clock
  int TwelveHour = Hours%12;
  if (TwelveHour==0) TwelveHour = 12;
  if (TwelveHour<10) Buffer[0] = Space; else Buffer[0] = TwelveHour/10;
  Buffer[1] = TwelveHour%10;
  Buffer[2] = Mins/10;
  Buffer[3] = Mins%10; 
  if (TimeValid) Buffer[3] = Buffer[3]+128; // Show colon
}