[avr-gcc-list] Problem with timing

[Juraj]

Hi all..

Perhaps, it is trivial problem, but I cannot find the bug.
Please help.

I have LED, connected to AVR. I want to get blinking LED, with 1:1
alternation: 
LED_ON - 500ms delay - LED_OFF - 500ms delay - LED_ON ...

Problem is - times are not always 500ms, some of periodes are shorter.


Thank you very much.

Juraj.








So here is part of main programm:

#include "timer.h"

int main(void) {
.
.
        timer0_init();
        while(1){
                LED_ON;         //sets the output 
                ms_delay(500);
                LED_OFF;        //clears the output
                ms_delay(500);  
        }
.
.
}


*******************************************************************************************

And here is timing module - timer.c:

#include <avr/timer.h>
#include <avr/interrupt.h>
#include <avr/signal.h>
#include <inttypes.h>
#include "casovac.h"

volatile uint32_t ms_timer = 0;


void timer0_init(void)
{
        timer_enable_int( BV(TOIE0) );
        timer0_source(CK64);
        TCNT0 = PRESCALE_LO;
}


SIGNAL(SIG_OVERFLOW0)                  // signal handler for tcnt0
overflow interrupt
{
        ms_timer++;                    // increment timer counter
        TCNT0 = PRESCALE_LO;   
}


void ms_delay(uint16_t ms )
{
uint32_t koniec = ms_timer + (uint32_t)ms;
        
        while( ms_timer < koniec );
}

*******************************************************************************************

And timer.h:

#define F_CPU           8000000         
#define PRESCALE_HI     64              
#define PRESCALE_LO     ( 256 - ( (F_CPU/PRESCALE_HI) / 1000 ) )  
                
extern volatile uint32_t ms_timer;

void timer0_init(void);
void ms_delay(uint16_t ms );

*******************************************************************************************




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