RTC.c

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/* This file has been prepared for Doxygen automatic documentation generation.*/
//  Include files
#include "Main.h"
#include "RTC.h"

// Lookup table used to determine the highest date in a specific month
unsigned char MaxDate[13] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};


void RTC_init(void)
{
    Delay(1000);            // wait for 1 sec to let the Xtal stabilize after a power-on,

    __disable_interrupt();  // disabel global interrupt

    TIMSK2 = 0;             // disable OCIE2A and TOIE2

    ASSR = (1<<AS2);        // select asynchronous operation of Timer2

    TCNT2 = 0;              // clear TCNT2A
    TCCR2A = (1<<CS22) | (1<<CS20);             // select precaler: 32.768 kHz / 128 = 1 sec between each overflow

    while(ASSR & (0x01 | 0x04));       // wait for TCN2UB and TCR2UB to be cleared

    TIFR2 = 0xFF;           // clear interrupt-flags
    TIMSK2 = (1<<TOIE2);    // enable Timer2 overflow interrupt

    __enable_interrupt();                 // enable global interrupt

    // initial time and date setting
    HOUR = 8;
    MINUTE = 0;
    SECOND = 0;
    DAY = 4;
    MONTH = 11;
    YEAR_LO = 2;
    YEAR_HI = 20;
}


void Time_update(void)
{
   unsigned char LeapYear = FALSE;

    //the variable SECOND gets updated in the Timer0 Overflow Interrupt Routine every second

    if(SECOND > 59)                         // if one minute
    {
        SECOND = 0;                         // clear SECOND
        MINUTE++;                           // increment MINUTE

        if(MINUTE > 59)                     // if one hour
        {
            MINUTE = 0;                     // clear MINUTE
            HOUR++;                         // increment HOUR

            if(HOUR > 23)                   // if one hour
            {
                HOUR = 0;                   // clear HOUR
                DAY++;                      // increment DAY

                if(MONTH == 2)              // if it's February
                {
                    // check for leap year
                    if(!YEAR_LO)                        // if YEAR_LO = 0, (a century has passed)
                    {
                        if(!(YEAR_HI%4))                // check if YEAR_HI is divisible by 4
                            LeapYear = TRUE;                // then it is a leap year
                    }
                    else if(!(YEAR_LO%4) & (YEAR_LO != 0))  // else if YEAR_LO is divisible by 4 and not zero
                        LeapYear = TRUE;                    // then it's a leap year
                }

                if(DAY > (MaxDate[MONTH] + LeapYear))   // if a whole month has passed
                {
                    DAY = 1;                // clear DAY
                    MONTH++;                // increment MONTH

                    if(MONTH > 12)          // if one year
                    {
                        MONTH = 1;          // clear MONTH
                        YEAR_LO++;          // increment YEAR_LO

                        if(YEAR_LO > 99)    // if one century
                        {
                            YEAR_LO = 0;    // clear YEAR_LO
                            YEAR_HI++;      // increment YEAR_HI

                            if(YEAR_HI > 99)    // if 100 centuries
                                YEAR_HI = 0;    // the AVR is still going strong :)
                        }
                    }
                }
            }
        }
    }
}


#pragma vector = TIMER2_OVF_vect
__interrupt void TIMER2_OVF_interrupt(void)
{
    SECOND++;               // increment second
}

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