Shouldnt these codes work the same, or i am messing something ?? because in CTC mode it doesnt work the same



Code 1:

#include <avr/io.h>
#include <avr/interrupt.h>
char x=0;

int main(void)
{
   DDRA=0xFF;
   PORTA=0x00;
  
   OCR0=0xFF;
   TIMSK=(1<<OCIE0);
   TCCR0=(1<CS00)|(1<CS02)|(1<WGM01);
   sei();
  
  while(1)
  {
  }
}
ISR(TIMER0_COMP_vect)
{
   if(x==4)
   {
     PORTA++;
     x=0;
     if (PORTA == 10)
     {
       PORTA=0;
     }
   }
   x++;
}

Code 2 :

#include <avr/io.h>
#include <avr/interrupt.h>

int x=0;

int main(void)
{
   DDRC|=0xf;
   PORTC=0x00;
  
   TCCR0=(1<<CS00)|(1<<CS02);
   TIMSK=(1<<TOIE0);
   sei();
  
  while(1)
  {
  }
}
ISR(TIMER0_OVF_vect)
{
   if(x==4)
   {
   if (PORTC==9)
   {
     PORTC=0;
     x=0;
   }
   else
   {
     PORTC+=1;
     x=0;
   }
   }
   x++;  
}

Moderators note: Please use code tags for pieces of code

 

First of all, for any Atmel questions, you might want to first try AVR Freaks at www.avrfreaks.net That's where the AVR experts hang out.
What exactly is it supposed to be doing, and what's misbehaving?
I'd start by declaring x as volatile. Otherwise the compiler may not see it in the ISR.

 

"The left shift instruction is written “LSL Rd” and its machine code is 0000 11dd dddd dddd (the bold d’s are replaced by the binary code for the register and the other d’s are replaced by the same five bits). How can this be? Interpret this instruction as an ADD instruction and see what it really does. Compare this to the effect of a logical shift left. Is there a problem?"


DdD DeViL

 

" Is there a problem?"
DdD DeViL

oh thx for ur reply, but some 1 in avr freaks already figured out the problem, look at TCCR register initialization how i used compare operator < instead of shift operator << dumb mistake, but thx anyway

 

I'd start by declaring x as volatile. Otherwise the compiler may not see it in the ISR.

x is a global variable, any function written in same file with main can see x

 

x is a global variable, any function written in same file with main can see x

Depends on the optimization. In subroutines, especially ISR's, the optimizer can do some strange things with global variables. Declaring it "volatile" ensures that the optimizer doesn't mess with it.