Microchip Technology SW006022-2N Data Sheet

DS52071B-page 88

 2012 Microchip Technology Inc.

/*

** Sample Real Time Clock for dsPIC

**

**  Uses Timer1, TCY clock timer mode

**  and interrupt on period match

*/

#include <xc.h>

/* Timer1 period for 1 ms with FOSC = 20 MHz */

#define TMR1_PERIOD 0x1388

struct clockType

  {

   unsigned int timer;     /* countdown timer, milliseconds */

   unsigned int ticks;     /* absolute time, milliseconds   */

   unsigned int seconds;   /* absolute time, seconds        */

  } volatile RTclock;

void reset_clock(void)

  {

   RTclock.timer = 0;      /* clear software registers  */

   RTclock.ticks = 0;

   RTclock.seconds = 0;

  

   TMR1 = 0;               /* clear timer1 register     */

   PR1 = TMR1_PERIOD;      /* set period1 register      */

   T1CONbits.TCS = 0;      /* set internal clock source */

   IPC0bits.T1IP = 4;      /* set priority level        */

   IFS0bits.T1IF = 0;      /* clear interrupt flag      */

   IEC0bits.T1IE = 1;      /* enable interrupts         */

   SRbits.IPL = 3;         /* enable CPU priority levels 4-7*/

   T1CONbits.TON = 1;      /* start the timer*/

  }

void 

_ _

attribute

_ _

((

__

interrupt

_ _

,

_ _

auto_psv

_ _

)) _T1Interrupt(void)

  { static int sticks=0;

    if (RTclock.timer > 0)   /* if countdown timer is active */

        RTclock.timer -= 1;  /*  decrement it               */

    RTclock.ticks++;         /* increment ticks counter     */

    if (sticks++ > 1000)

    {                           /* if time to rollover         */

    sticks = 0;              /*  clear seconds ticks     */

    RTclock.seconds++;       /*  and increment seconds   */

    }

    

    IFS0bits.T1IF = 0;       /* clear interrupt flag     */

    return;

  }