ulTaskNotifyTake() for binary/counting notification in FreeRTOS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of ulTaskNotifyTake() with clear count on binary notification?

Consider a FreeRTOS task that calls ulTaskNotifyTake(pdTRUE, 0) after receiving a single notification. What value does ulTaskNotifyTake() return?

FreeRTOS

/* Assume the task has received exactly one notification count before this call */
uint32_t count = ulTaskNotifyTake(pdTRUE, 0);
printf("%u", count);

A 1

B 2

C 0

D Error: function blocks and never returns

💡 Hint

Think about what pdTRUE does to the notification count.

When ulTaskNotifyTake(pdTRUE, 0) is called, it returns the current notification count and then clears it to zero. Since the task had exactly one notification, the function returns 1.

❓ Predict Output

intermediate

What does ulTaskNotifyTake() return after multiple notifications with clear count?

A task receives 3 notifications before calling ulTaskNotifyTake(pdTRUE, 0). What is the return value?

FreeRTOS

/* Notifications sent 3 times before this call */
uint32_t count = ulTaskNotifyTake(pdTRUE, 0);
printf("%u", count);

A Error: function blocks indefinitely

B 1

C 0

D 3

💡 Hint

Count accumulates with counting notifications.

Each notification increments the count. Calling ulTaskNotifyTake(pdTRUE, 0) returns the total count (3) and clears it.

❓ Predict Output

advanced

What happens if ulTaskNotifyTake() is called with clear count false on a counting notification?

A task has a notification count of 2. It calls ulTaskNotifyTake(pdFALSE, 0). What is the return value and the new notification count?

FreeRTOS

/* Notification count is 2 before call */
uint32_t count = ulTaskNotifyTake(pdFALSE, 0);
printf("%u", count);
// What is the notification count now?

A Returns 2; notification count resets to 0

B Returns 2; notification count remains 2

C Returns 0; notification count remains 2

D Returns 1; notification count decrements to 1

💡 Hint

Clear count flag controls if count resets after reading.

With pdFALSE, the count is returned but not cleared, so it stays at 2.

❓ Predict Output

advanced

What is the behavior of ulTaskNotifyTake() with timeout when no notification is pending?

A task calls ulTaskNotifyTake(pdTRUE, 10) but no notification is pending. What happens?

FreeRTOS

uint32_t count = ulTaskNotifyTake(pdTRUE, 10);
printf("%u", count);

A Returns immediately with 0

B Returns immediately with 1

C Blocks up to 10 ticks, then returns 0 if no notification received

D Blocks indefinitely until notification received

💡 Hint

Timeout controls how long the function waits for notification.

The function blocks up to the timeout (10 ticks). If no notification arrives, it returns 0.

🧠 Conceptual

expert

How does ulTaskNotifyTake() differ from xTaskNotifyWait() in counting notifications?

Which statement correctly describes the difference between ulTaskNotifyTake() and xTaskNotifyWait() when used for counting notifications?

A <code>ulTaskNotifyTake()</code> returns the current count and optionally clears it; <code>xTaskNotifyWait()</code> waits for a notification and returns a status but does not count.

B <code>ulTaskNotifyTake()</code> decrements the notification count by one per call; <code>xTaskNotifyWait()</code> reads and clears the notification value.

C <code>ulTaskNotifyTake()</code> only works for binary notifications; <code>xTaskNotifyWait()</code> only works for counting notifications.

D <code>ulTaskNotifyTake()</code> blocks indefinitely; <code>xTaskNotifyWait()</code> never blocks.

💡 Hint

Think about what each function returns and how they handle notification counts.

ulTaskNotifyTake() returns the notification count and optionally clears it, useful for counting notifications. xTaskNotifyWait() waits for a notification and returns a status indicating if one was received, but does not provide the count.