Volatile variables in ISR context in Embedded C - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a variable that can change unexpectedly in an ISR.

Embedded C

volatile int [1] = 0;

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

Aflag

Btemp

Ccounter

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-volatile variable for data changed in ISR.

Choosing a variable name unrelated to counting.

The variable counter is declared as volatile because it can be changed inside an ISR.

2fill in blank

medium

Complete the code to correctly declare a flag variable modified inside an ISR.

Embedded C

volatile [1] flag = 0;

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

Aint

Bchar

Cfloat

Ddouble

Attempts:

3 left

💡 Hint

Common Mistakes

Using floating point types for flags.

Not declaring the variable as volatile.

The flag is declared as a volatile int because it is modified in an ISR and used in main code.

3fill in blank

hard

Fix the error in the ISR by correctly declaring the variable as volatile.

Embedded C

void ISR_Handler() {
    [1] count;
    count++;
}

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

Aint

Bconst int

Cstatic int

Dvolatile int

Attempts:

3 left

💡 Hint

Common Mistakes

Using const or static instead of volatile.

Omitting volatile keyword.

The variable count must be declared as volatile int to ensure the compiler does not optimize away accesses in the ISR.

4fill in blank

hard

Fill both blanks to declare and use a volatile flag in main and ISR.

Embedded C

volatile int [1] = 0;

void ISR() {
    [2] = 1;
}

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

Aflag

Bcounter

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names in declaration and ISR.

Not declaring the variable as volatile.

The variable flag is declared volatile and set to 1 inside the ISR.

5fill in blank

hard

Fill all three blanks to declare a volatile counter, increment it in ISR, and check it in main.

Embedded C

volatile int [1] = 0;

void ISR() {
    [2]++;
}

int main() {
    if ([3] > 0) {
        // handle event
    }
    return 0;
}

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

Aevent_count

Dcounter

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names in different places.

Not declaring the variable as volatile.

The variable event_count is declared volatile, incremented in ISR, and checked in main.