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WDTCR ATtiny

#1 · December 14, 2025, 2:04 pm

I could not update WDTCR for it has written data 00101111 from the start and not possible to update.

Is it a bug or I do something wrong?

Thanks

#2 · December 14, 2025, 3:59 pm

Hi.

Can you share your code to try to reproduce the issue?

#3 · December 14, 2025, 7:27 pm

#include <avr/interrupt.h>

#define LED_BIT _BV(PB1)

ISR(WDT_vect){
  PORTB &= ~LED_BIT;
}

int main()
{
  DDRB |= LED_BIT; // OUTPUT
  PORTB |= LED_BIT;
  cli(); 
  GIMSK |= _BV(PCIE);  
  wdt_reset();                                            
  WDTCR |= _BV(WDCE) | _BV(WDE);                //enable write
  WDTCR  = _BV(WDTIE) | _BV(WDP2) | _BV(WDP1);   //enable interrupt + 128k cycles 
  sei();                                            
                                                                                 
  while (1)
  {
  }
}

The app very simple, I expect that in 1 sec the led should off. Bits WDP* always 1 and no interrupt.

Thanks a lot.

Uploaded files:

wdt.sim1

#4 · December 15, 2025, 6:41 pm

a question, this flag means WDTON fuse?

#5 · December 16, 2025, 10:48 am

Quote from yurimoisa on December 15, 2025, 6:41 pm

Hi

a question, this flag means WDTON fuse?

Yes, it is basically WDTON fuse.

#6 · December 16, 2025, 12:49 pm

ok, thanks

Have you discovered why it is not possible to change WDP* bits in WDTCR? They are always "1".

#7 · December 16, 2025, 12:51 pm

Quote from yurimoisa on December 16, 2025, 12:49 pm

ok, thanks

Have you discovered why it is not possible to change WDP* bits in WDTCR? They are always "1".

Not yet.

By the way: which ATtiny are you using?

#8 · December 16, 2025, 2:03 pm

The problem comes from interrupt bit names WDTIE and WDTIF. The default for most devices is WDIE and WDIF.

You can fix it by editing the file: simulide/data/AVR/tiny13/tiny13_regs.xml
At line 32 add an alias for the bit names like this:

               bits="WDP0,WDP1,WDP2,WDE,WDCE,WDP3,WDTIE|WDIE,WDTIF|WDIF" />

#9 · December 16, 2025, 9:49 pm

thanks again, now WDT works well.

The only thing is that the bits WDP are always 1 in the monitor though in fact the watch dog cycle is correct exacly as it was set in the program.

#10 · December 16, 2025, 10:27 pm

Quote from yurimoisa on December 16, 2025, 9:49 pm

The only thing is that the bits WDP are always 1 in the monitor though in fact the watch dog cycle is correct exacly as it was set in the program.

Thank you, I will solve that issue.