Writing an ISR (Interrupt Service Routine) in Embedded C - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an ISR function for TIMER0 overflow.

Embedded C

void TIMER0_OVF_vect(void) [1] {
    // ISR code here
}

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A__interrupt

Bvoid

CISR

Dinterrupt

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'void' instead of 'interrupt' keyword.

Forgetting to declare the function as an ISR.

The keyword 'interrupt' is used to declare an ISR function in embedded C for many compilers.

2fill in blank

medium

Complete the code to enable the TIMER0 overflow interrupt by setting the correct bit.

Embedded C

TIMSK |= (1 << [1]);

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ATOIE1

BOCIE0

CTOIE0

DOCIE1

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing bits related to TIMER1 instead of TIMER0.

Using Output Compare Interrupt Enable bits instead of Overflow.

TOIE0 is the Timer/Counter0 Overflow Interrupt Enable bit.

3fill in blank

hard

Fix the error in the ISR declaration syntax.

Embedded C

void [1](void) interrupt 5 {
    // ISR code
}

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ATIMER0_OVF_vect

BISR_TIMER0

CTIMER1_OVF_vect

DISR

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect ISR function names.

Using generic names like 'ISR' without vector suffix.

The correct ISR name for TIMER0 overflow is 'TIMER0_OVF_vect' in many embedded C compilers.

4fill in blank

hard

Fill both blanks to correctly clear the interrupt flag inside the ISR.

Embedded C

void TIMER1_OVF_vect(void) {
    [1] &= ~(1 << [2]); // Clear interrupt flag
}

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ATIFR

BTIMSK

CTOV1

DOCF1A

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to clear flags in TIMSK instead of TIFR.

Using wrong flag bits like OCF1A.

The interrupt flag for TIMER1 overflow is TOV1, and it is cleared by writing 0 to the bit in TIFR register.

5fill in blank

hard

Fill all three blanks to write an ISR that increments a counter and clears the interrupt flag.

Embedded C

volatile int counter = 0;

void [1](void) {
    counter[2];
    [3] &= ~(1 << TOV0);
}

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ATIMER0_OVF_vect

B++

CTIFR

DTIMSK

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong ISR names.

Using += 1 instead of ++ (though valid, ++ is simpler here).

Clearing flags in TIMSK instead of TIFR.

The ISR name is TIMER0_OVF_vect, increment operator is ++, and the interrupt flag register is TIFR.