ISR-safe API functions (FromISR suffix) in FreeRTOS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to send a character to a queue safely from an ISR.

FreeRTOS

BaseType_t xHigherPriorityTaskWoken = pdFALSE;
xQueueSendFromISR(queue, &[1], &xHigherPriorityTaskWoken);

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

Aitem

Bdata

Cvalue

Dcharacter

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable not declared or unrelated to the data to send.

Forgetting to pass the address of the data.

The variable data holds the character to send to the queue from the ISR.

2fill in blank

medium

Complete the code to yield from an ISR if a higher priority task was woken.

FreeRTOS

if (xHigherPriorityTaskWoken [1] pdTRUE) {
    portYIELD_FROM_ISR();
}

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A<

B!=

C>

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using inequality operator which causes incorrect behavior.

Using comparison operators like < or > which are not appropriate here.

The condition checks if xHigherPriorityTaskWoken is equal to pdTRUE to decide if a context switch is needed.

3fill in blank

hard

Fix the error in the ISR-safe queue receive function call.

FreeRTOS

BaseType_t result = xQueueReceiveFromISR(queue, [1], NULL);

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A&buffer

Bbuffer

C*buffer

Dbuffer[0]

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the buffer variable directly instead of its address.

Dereferencing the buffer which causes errors.

The function expects a pointer to the buffer, so &buffer is correct.

4fill in blank

hard

Fill both blanks to correctly send data from an ISR and handle task wakeup.

FreeRTOS

BaseType_t xHigherPriorityTaskWoken = pdFALSE;
if (xQueueSendFromISR(queue, &[1], &[2]) != pdPASS) {
    // Handle error
}

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Adata

BxHigherPriorityTaskWoken

CxTaskWoken

Dresult

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect variable names for the task wakeup flag.

Not passing the address of the data variable.

data is the variable sent to the queue, and xHigherPriorityTaskWoken tracks if a higher priority task was woken.

5fill in blank

hard

Fill all three blanks to create an ISR-safe queue send and yield if needed.

FreeRTOS

BaseType_t [1] = pdFALSE;
if (xQueueSendFromISR(queue, &[2], &[3]) == pdPASS) {
    portYIELD_FROM_ISR([3]);
}

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

AxHigherPriorityTaskWoken

Bdata

Dresult

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names inconsistently.

Not passing the address of the data variable.

xHigherPriorityTaskWoken is declared and used to track if a higher priority task was woken. data is the variable sent to the queue.