FreeRTOS interrupt priority restrictions - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define the maximum interrupt priority from which FreeRTOS API functions can be called.

FreeRTOS

#define configMAX_SYSCALL_INTERRUPT_PRIORITY [1]

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A5

B1

C0

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Setting the priority to 0, which is the highest priority and can cause system instability.

The macro configMAX_SYSCALL_INTERRUPT_PRIORITY sets the highest interrupt priority that can safely call FreeRTOS API functions.

2fill in blank

medium

Complete the code to mask interrupts above the maximum syscall priority in FreeRTOS.

FreeRTOS

portENTER_CRITICAL();
uint32_t priority = [1];
portEXIT_CRITICAL();

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AconfigMAX_SYSCALL_INTERRUPT_PRIORITY

BconfigKERNEL_INTERRUPT_PRIORITY

CconfigMIN_SYSCALL_INTERRUPT_PRIORITY

DconfigMAX_INTERRUPT_PRIORITY

Attempts:

3 left

💡 Hint

Common Mistakes

Using configKERNEL_INTERRUPT_PRIORITY which is the lowest priority, not the maximum syscall priority.

Interrupts with priority above configMAX_SYSCALL_INTERRUPT_PRIORITY are masked to protect critical sections.

3fill in blank

hard

Fix the error in the interrupt handler priority check to ensure it complies with FreeRTOS restrictions.

FreeRTOS

void ISR_Handler(void) {
    if (NVIC_GetPriority(IRQn) [1] configMAX_SYSCALL_INTERRUPT_PRIORITY) {
        // Safe to call FreeRTOS API
    }
}

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A>=

B!=

C==

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<=' which would allow interrupts with too high priority (numerically low values) to call FreeRTOS APIs.

Interrupts with priority numerically greater or equal to configMAX_SYSCALL_INTERRUPT_PRIORITY can safely call FreeRTOS APIs.

4fill in blank

hard

Fill both blanks to correctly define the interrupt priority grouping and the maximum syscall priority.

FreeRTOS

NVIC_SetPriorityGrouping([1]);
#define configMAX_SYSCALL_INTERRUPT_PRIORITY [2]

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ANVIC_PRIORITYGROUP_4

BNVIC_PRIORITYGROUP_2

C5

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing priority grouping values or setting max syscall priority incompatible with grouping.

Priority grouping NVIC_PRIORITYGROUP_4 is commonly used with FreeRTOS, and the max syscall priority is set to 3 in this example.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps interrupt names to their priorities, filtering only those with priority less than the max syscall priority.

FreeRTOS

irq_priorities = {irq: [1] for irq, prio in irq_list.items() if prio [2] [3]

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Aprio

B<

CconfigMAX_SYSCALL_INTERRUPT_PRIORITY

Dirq

Attempts:

3 left

💡 Hint

Common Mistakes

Using the interrupt name instead of priority as the dictionary value.

Using wrong comparison operators.

This comprehension creates a dictionary of interrupts with priorities less than the max syscall priority, mapping IRQ names to their priority values.