SEG 4145 Software Engineering - Quiz 3 Participation Review: RTOS Scheduling, TrustZone Memory Security, and Interrupt Handling

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University of Ottawa



Software Engineering - Quiz 3 Participation
Review: RTOS Scheduling, Trust Zone
Memory Security, and Interrupt Handling




Course: SEG 4145

,Question 1 — Préemption vs time slicing (piège conceptuel)

#define configUSE_PREEMPTION 1

#define configUSE_TIME_SLICING 1



const osThreadAttr_t Task1_attributes = { .priority = 3 };

const osThreadAttr_t Task2_attributes = { .priority = 2 };

const osThreadAttr_t Task3_attributes = { .priority = 2 };



void StartTask1(void *argument)

{

for(;;) { countTask1++; } // never blocks

}



void StartTask2(void *argument)

{

for(;;) { countTask2++; }

}



void StartTask3(void *argument)

{

for(;;) { countTask3++; }

}

Question:
Which statement best describes the runtime behavior?

A. Task2 and Task3 alternate fairly because time slicing is enabled
B. All three tasks share CPU time equally

, C. Task1 dominates execution; Task2 and Task3 may never run
D. Task2 and Task3 preempt Task1 periodically

Correct answer: C

Key idea:
Time slicing does NOT override priority. Preemption ensures the highest-priority READY
task always runs.



Question 2 — Time slicing only among equals

#define configUSE_PREEMPTION 1

#define configUSE_TIME_SLICING 1



const osThreadAttr_t Task1_attributes = { .priority = 2 };

const osThreadAttr_t Task2_attributes = { .priority = 2 };

const osThreadAttr_t Task3_attributes = { .priority = 2 };



void StartTask1(void *argument) { for(;;) { countTask1++; } }

void StartTask2(void *argument) { for(;;) { countTask2++; } }

void StartTask3(void *argument) { for(;;) { countTask3++; } }

Question:
What is the most accurate description?

A. Only the first-created task runs continuously
B. Tasks run one after another in a fixed order
C. Tasks alternate execution in time slices
D. The task with the smallest stack runs more often

Correct answer: C

Key idea:
With configUSE_TIME_SLICING = 1, equal-priority READY tasks share the CPU.