Interrupt Handling – Real-time Systems MCQs

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1. What is the main purpose of interrupt handling in real-time systems?
(A) To allow the system to respond to external events quickly
(B) To increase CPU idle time
(C) To delay task execution intentionally
(D) To ignore periodic tasks

2. An interrupt is:
(A) A signal that temporarily halts normal task execution to attend an event
(B) A type of periodic task
(C) A scheduling algorithm
(D) A memory allocation scheme

3. Which component in RTOS handles interrupts?
(A) Task scheduler only
(B) Mutex
(C) Interrupt Service Routine (ISR)
(D) Semaphore

4. What is the main characteristic of an ISR?
(A) It executes quickly and returns control to the interrupted task
(B) It executes with a fixed period
(C) It ignores hardware events
(D) It runs only after all tasks complete

5. In real-time systems, interrupts are classified as:
(A) Batch and background tasks
(B) Periodic and aperiodic tasks only
(C) Soft and hard tasks
(D) Hardware and software interrupts

6. Which of the following is TRUE about hardware interrupts?
(A) They are generated by external devices or peripherals
(B) They are generated by task scheduler only
(C) They occur periodically always
(D) They ignore task priorities

7. Software interrupts are:
(A) Ignored by the system
(B) Only generated by hardware
(C) Non-preemptive
(D) Generated by programs or RTOS services

8. Nested interrupts occur when:
(A) Deadlines are ignored
(B) Tasks execute sequentially without preemption
(C) CPU is idle
(D) An interrupt occurs while another interrupt is being serviced

9. Interrupt latency is defined as:
(A) WCET of the task
(B) Task execution time
(C) Task period
(D) Time between the interrupt occurrence and the start of its ISR

10. In RTOS, interrupt handling is critical to:
(A) Ignore task priorities
(B) Increase CPU idle time
(C) Delay task execution
(D) Ensure timely response to external and internal events

11. Which mechanism ensures high-priority interrupts are serviced first?
(A) Batch processing
(B) Round-robin scheduling
(C) Priority-based interrupt handling
(D) Periodic task execution

12. What is the main disadvantage of long ISRs?
(A) They increase system latency for other tasks and interrupts
(B) They reduce WCET
(C) They decrease task periods
(D) They ignore deadlines automatically

13. Deferred interrupt handling can be achieved using:
(A) Ignoring hardware interrupts
(B) Non-preemptive scheduling only
(C) Task-level interrupt handling or interrupt service threads
(D) WCET reduction only

14. Which RTOS component manages interrupt priorities and masking?
(A) Interrupt controller
(B) Task scheduler only
(C) Memory manager
(D) Mutexes

15. In real-time systems, masking an interrupt means:
(A) Ignoring deadlines
(B) Executing it immediately
(C) Temporarily disabling it to prevent ISR execution
(D) Preempting all tasks

16. Spurious interrupts are:
(A) Periodic tasks
(B) High-priority interrupts
(C) False or unintended interrupts triggered without a valid cause
(D) Task deadlines

17. What is the effect of high interrupt frequency on RTOS performance?
(A) It reduces task WCET
(B) It can increase CPU overhead and delay task execution
(C) It decreases memory usage
(D) It increases task periods only

18. Bottom-half processing in interrupt handling refers to:
(A) Preempting high-priority tasks
(B) Executing all work inside the ISR
(C) Ignoring interrupts temporarily
(D) Deferring non-critical work from ISR to a task-level handler

19. Real-time systems aim to minimize interrupt latency to:
(A) Increase CPU idle time
(B) Ensure predictable and timely response to critical events
(C) Reduce task priorities
(D) Ignore deadlines

20. Which of the following is a best practice for ISRs in RTOS?
(A) Keep them short and fast, defer heavy processing to tasks
(B) Execute all work inside ISR
(C) Ignore interrupt priorities
(D) Use batch processing for interrupts