Nested interrupts in Embedded C - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to enable global interrupts.

Embedded C

#include <avr/interrupt.h>

int main() {
    sei(); // Enable global interrupts
    [1];
    while(1) {}
    return 0;
}

Drag options to blanks, or click blank then click option'

Aenable_interrupts()

Bcli()

Cinterrupt_enable()

Dsei()

Attempts:

3 left

💡 Hint

Common Mistakes

Using cli() which disables interrupts instead of enabling them.

Using non-standard function names.

The sei() function enables global interrupts in AVR microcontrollers.

2fill in blank

medium

Complete the code to define an interrupt service routine (ISR) for TIMER1 overflow.

Embedded C

#include <avr/interrupt.h>

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

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AINT0_vect

BTIMER0_OVF_vect

CTIMER1_OVF_vect

DADC_vect

Attempts:

3 left

💡 Hint

Common Mistakes

Using TIMER0_OVF_vect which is for TIMER0.

Using unrelated interrupt vectors.

The ISR for TIMER1 overflow uses the vector TIMER1_OVF_vect.

3fill in blank

hard

Fix the error in the ISR declaration to allow nested interrupts by enabling global interrupts inside the ISR.

Embedded C

ISR(TIMER2_OVF_vect) {
    [1](); // Enable nested interrupts
    // ISR code
}

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Acli

Bsei

Cenable_global_interrupts

Dinterrupt_enable

Attempts:

3 left

💡 Hint

Common Mistakes

Using cli() which disables interrupts.

Using non-standard function names.

Calling sei() inside an ISR enables nested interrupts by setting the global interrupt flag.

4fill in blank

hard

Fill both blanks to create a nested interrupt safe ISR that enables global interrupts and clears the interrupt flag.

Embedded C

ISR(ADC_vect) {
    [1](); // Enable nested interrupts
    ADCSRA [2] (1 << ADIF); // Clear interrupt flag
}

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Asei

B|=

C&=

Dcli

Attempts:

3 left

💡 Hint

Common Mistakes

Using cli() instead of sei() to enable interrupts.

Using &= which clears bits instead of setting them.

Inside the ISR, sei() enables nested interrupts. The interrupt flag is cleared by setting the ADIF bit using |=.

5fill in blank

hard

Fill all three blanks to implement a nested interrupt safe ISR that enables global interrupts, clears the interrupt flag, and increments a counter.

Embedded C

volatile uint8_t count = 0;

ISR(INT0_vect) {
    [1](); // Enable nested interrupts
    EIFR [2] (1 << INTF0); // Clear interrupt flag
    [3]++; // Increment counter
}

Drag options to blanks, or click blank then click option'

Asei

B|=

Ccount

Dcli

Attempts:

3 left

💡 Hint

Common Mistakes

Using cli() instead of sei() to enable interrupts.

Using &= instead of |= to clear the flag.

Incrementing a wrong or undefined variable.

Inside the ISR, sei() enables nested interrupts, EIFR |= (1 << INTF0) clears the interrupt flag, and count++ increments the counter.