Re: [avr-gcc-list] Problem with timing

[Keith Gudger]

Where is ms_timer set and reset to 0?  Shouldn't your code be:

        while( ms_timer < koniec );
        ms_timer = 0 ;
}

Keith


On Tue, 3 Feb 2004, Juraj wrote:

> 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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> 
> 
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