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uncontrollable timer interrupt frequency

 
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Liv



Joined: 09 May 2012
Posts: 6

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uncontrollable timer interrupt frequency
PostPosted: Wed May 09, 2012 7:29 am     Reply with quote

Greetings members,

It's my first, so be gentle Smile
The following code generates a clock interrupt.
The problem is that the it's frequency is uncontrollable...
To my understanding beyond the setup, what control the frequency is the value set by: set_timer1() in the ISR.
But what ever value I set, the IRQ frequency does not change. Although the value that get_timer1() returns is changing accordingly(!).

Thank you in advance,
Liv.

Code:

#include <18F6527.h>

#fuses HS, PUT, NOLVP, MCLR, NOPROTECT
#FUSES WDT8192         //Watch Dog Timer uses 1:128 Postscale
#FUSES BROWNOUT        //Reset when brownout detected
#FUSES BORV27          //Brownout reset at 2.5V //was BORV25
#FUSES NOCPD           //No EE protection
#FUSES STVREN          //Stack full/underflow will cause reset
#FUSES NOWRT           //Program memory not write protected
#FUSES NOWRTD          //Data EEPROM not write protected
#FUSES NOIESO          //Internal External Switch Over mode enabled
#FUSES NOFCMEN         //Fail-safe clock monitor enabled
#FUSES NOWRTC          //configuration not registers write protected
#FUSES NOWRTB          //Boot block not write protected
#FUSES NOEBTRB         //Boot block not protected from table reads
#FUSES NOLPT1OSC       //Timer1 configured for low-power operation
#use delay(clock=22118400)

unsigned int16 lStatus = 0x0000;
#INT_TIMER1       
void clock_isr()
{
   set_timer1(0x2800);      //   10 mS
   lStatus = get_timer1();
}

void main()
{
   setup_timer_1(T1_INTERNAL);
   set_timer1(0);
   enable_interrupts(INT_TIMER1);
   enable_interrupts(GLOBAL);
   
   while(true)
   {
      //dummy operation
   }
}
jeremiah



Joined: 20 Jul 2010
Posts: 1343

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PostPosted: Wed May 09, 2012 7:58 am     Reply with quote

How are you determining that the IRQ frequency isn't changing? How is that measured?
Liv



Joined: 09 May 2012
Posts: 6

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PostPosted: Wed May 09, 2012 8:09 am     Reply with quote

From the ISR I toggle a led, and measure it’s contact voltage with an oscilloscope.
jeremiah



Joined: 20 Jul 2010
Posts: 1343

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PostPosted: Wed May 09, 2012 8:33 am     Reply with quote

Have you verified that your oscillator is running at the values you have set? I.E. have you run:

Code:

void main(){
   while(TRUE){
      delay_us(500);
      output_toggle(DEBUG_PIN);
   }

}


And what did the frequency measure at?

Also, what frequency do you measure for the ISR frequency?

If you change

set_timer1(0x2800);

to

set_timer1(0xEA66);

are there any changes in that value?
Liv



Joined: 09 May 2012
Posts: 6

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PostPosted: Wed May 09, 2012 10:12 am     Reply with quote

Mystery solved! location, location, location...

The clock definition was in the module that includes the main and initialization functions. The ISR is in different module. I copied the clock definition to just before the ISR and miracle of miracles, the ISR frequency is controllable! (Changing the set_timer1() value change the frequency).

Thanks guys, I learned something new.
ckielstra



Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands

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PostPosted: Wed May 09, 2012 11:38 am     Reply with quote

Uhhhmmm.... you mean the code you posted here is not the same as you were testing with???? Rolling Eyes
Liv



Joined: 09 May 2012
Posts: 6

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PostPosted: Wed May 09, 2012 12:01 pm     Reply with quote

The code is more them 18000 lines in 13 files…
The posted code is a collection of two isolated parts that I considered relevant.
Sorry for any confusion… and I hope that others can benefit too from this post.
Mike Walne



Joined: 19 Feb 2004
Posts: 1785
Location: Boston Spa UK

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PostPosted: Wed May 09, 2012 12:49 pm     Reply with quote

Maybe next time you follow CCS forum guide, i.e. post complete compilable code so we can test to help sort out your problem.

Mike
Liv



Joined: 09 May 2012
Posts: 6

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PostPosted: Wed May 09, 2012 1:40 pm     Reply with quote

And that's precisely what I attempted to do.
Appreciate the assistance, as well, as the comments.
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