20 December 2010

multiple delay

This example shows you how to create multiple non-blocking delays with only one timer, using :
  • timer 1
  • interrupts
  • arrays of pointers to functions
  • structures
It is made for a P18F452 but it could be used with others pics with just minor adjustments.
The binary code is less than 2K, so that you can use the unlicenced mikroC compiler to build the HEX file.
This example can be discussed in the forum.

/*

 * this source code shows how to use pic timers, interrupts, and arrays of pointers to functions

 * and how to make non-blocking multiples delays, using a single timer

  *

 * Bruno Gavand, march 2006

 * www.micro-examples.com

 *

 * P18F452 @8Mhz, HS clock, EASYPIC2 / EASYPIC3

 * pull-down on PORTB

 * pull-up on keyboard

 * enable PORTB, PORTC and PORTD LEDs

  *

 * pressing RB0 key will toggle PORTC after a 2s non-blocking delay

 * pressing RB1 key will toggle PORTD after a 3s non-blocking delay

 *

 * used ROM : 1676 bytes

 */



/*

 * number of delayed keys, up to 255

  */

#define NBKEYS  2



/*

 * struct for one key

 */

typedef struct

        {

        unsigned char   flag ;          // active = 1, 0 otherwise

        unsigned char   ctr ;           // counter of timer1 overflows

         void            (*stop)() ;     // pointer to a function to call after delay

        } KEY_STRUCT ;

        

KEY_STRUCT      keys[NBKEYS] ;          // struct array



/*

 * functions that do something visible for the example

  */

void    toggleC()

        {

        PORTC = ~PORTC ;        // invert PORTC (toggle LEDs)

        }



void    toggleD()

        {

        PORTD = ~PORTD ;        // invert PORTD (toggle LEDs)

         }



/*

 * start to count down d milliseconds for key i

 */

void    keyStart(unsigned char i, unsigned long d)

        {

        KEY_STRUCT *k ;

        

        k = &keys[i] ;                          // struct pointer

         if(k->flag == 0)                        // if free ?

                {

                d <<= 18 ;                      // multiply by 4 * 2 ^ 16

                d /= 1000 ;                     // divide by 1000 because

                 d /= (long)Clock_Khz() ;        // clock frequency is known in Khz

                k->ctr = d ;                    // assign counter

                k->flag = 1 ;                   // set flag to start countdown in interrupt

                 }

        }



/*

 * interrupt vector

 */

void    interrupt()

        {

        if(PIR1.TMR1IF)         // timer1 overflow, Fosc/(4 * 2^16) times per second

                {

                unsigned char i ;

                 

                for(i = 0 ; i < NBKEYS ; i++)   // for each keys

                        {

                        KEY_STRUCT      *k ;

                        

                        k = &keys[i] ;          // get pointer to the key struct

                         if(k->flag)             // if key countdown activated

                                {

                                if(k->ctr)      // if countdown in progress

                                        {

                                         k->ctr-- ;      // count down

                                        }

                                else

                                        {

                                        k->flag = 0 ;   // count down reached 0, disable

                                         (k->stop)() ;   // call user's function

                                        }

                                }

                        }

                PIR1.TMR1IF = 0 ;               // reset timer1 interrupt flag

                 }

        }



/*

 * program starts here

 */

void main()

        {

        unsigned char   i ;

        

        ADCON1 |= 0x07;                         //  PORTA as digital I/O

         PORTA = PORTB = PORTC = PORTD = 0 ;     //  clear ports

        TRISA = 0 ;                             // PORTA as output

        TRISB = 0b00000011 ;                    // 2 LSB of PORTB as inputs, others as outputs

         TRISC = 0 ;                             // PORTC as output

        TRISD = 0 ;                             // PORTD as output



        keys[0].stop = toggleC ;                // assign user's function to first key

         keys[1].stop = toggleD ;                // assign user's function to second key

        

        for(i = 0 ; i < NBKEYS ; i++)           // for each keys

                {

                keys[i].flag = 0 ;              // reset struct

                 keys[i].ctr = 0 ;

                }

        

        T1CON.T1CKPS1 = 0 ;                     // no prescaler

        T1CON.T1CKPS0 = 0 ;                     // on timer1

        T1CON.T1OSCEN = 0 ;                     // disable timer1 oscillator

         T1CON.TMR1CS = 0 ;                      // timer1 is on Fosc

        T1CON.TMR1ON = 1 ;                      // start timer1



        INTCON.GIE = 1 ;                        // enable global interrupts

         INTCON.PEIE = 1 ;                       // enable peripheral interrupts



        PIE1.TMR1IE = 1 ;                       // enable timer1 overflow interrupts



        for(;;)                                 // forever

                 {

                if(PORTB.F0)                    // if RB0 key pressed

                        {

                        keyStart(0, 2000) ;     // start key #0 countdown for 2000 ms

                        }

                 else if(PORTB.F1)               // if RB1 key pressed

                        {

                        keyStart(1, 3000) ;     // start key #1 countdown for 3000 ms

                        }

                }

         }

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