Embedded and Real Time Operating Systems.
Questions from unit V and VI (partial)
Please use the following questions s study aids. You can easily answer them while browsing through the chapter sequentially.
Chapter 7 : Embedded and Real Time Operating Systems : Dr KVKK Prasad
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1. The embedded software consists of the _____ _____ and the _______ _______.
2. Explain the main difference between a soft real-time system and a hard real-time system.
3. How are the services provided by the OS accessed by an application ?
4. What is an API ?
5. List the kernel objects.
6. How are kernel objects managed ?
7. What are the services provided by the kernel ?
8. Define a task. What does it contain ? How is it implemented ?
9. What are system tasks ?
10. How should the tasks share a single CPU ?How is this achieved ?
11. What is a scheduler ?
12. What are the important issues that must be considered while scheduling the tasks ?
13. What is a reentrant function ? What is a non-reentrant function ?
14. How can you check whether a function is re-entrant or non re-entrant ?
15. What is the critical section of a code ?
16. Which kernel objects are used to share resources ?
17. How is inter task communication achieved ?
18. How many states may a task have ? Define each one of them.
19. How or when does a task move from one state to another ?
20. What is stored in a task stack ?
21. What is preempting ? What is a context ?
22. What is context switching ?
23. How does the kernel decide which task has to run ?
24. List the various scheduling algorithms that are used to control tasks.
25. Why is the FIFO algorithm not suited for many applications ? When is it most suited ?
26. What is round-robin algorithm ? What is a quantum ? When will the kernel give control to the next task ? What are the limitations of this algorithm ? When is it useful ?
27. What is round-robin with priority ?
28. What is the advantage of shortest-job first algorithm ? Does it have some kind of priority build-in ? Explain.
29. Why are the above scheduling algorithms not suitable for hard real-time systems ?
30. What are the two multi-tasking algorithms ?
31. Is non-preemptive multitasking different from cooperative multitasking ? Explain the basis for your answer.
32. Why is non-preemptive multitasking not suitable for embedded real-time systems ?
33. Explain the mechanism of preemptive multi-tasking.
34. Why is preemptive multi-tasking attractive ? Explain.
35. Why do most real time embedded systems use preemptive multi-tasking ?
36. What is a dispatcher ? Where is it ?
37. In how many ways can priority be assigned to a task ?
38. What is RMA ? Why and how is it useful in priority allocations ? What are its assumptions ?
39. What is schedulability test ? What does it indicate ?
40. Write the equation for utilization factor. What is the thumb rule ?
41. What is the basis for assigning priorities ?
42. Does the API provide a function to change the priority of a task ?
43. Define interrupt. What happens when an interrupt occurs ?
44. Define interrupt latency, interrupt response time, interrupt recovery time.
45. Compare interrupt recovery times in preemptive and non preemptive kernels.
46. “Semaphore is a kernel object that is used for both resource synchronization and task synchronization”. Explain.
47. When two tasks (task 1 and task2 ) are sharing a resource, with task 1 currently using the resource and task2 waiting, who informs task2 when task1 has completed using the resource and task2 can now use it ? What is this called ?
48. When many tasks share a resource, they are kept in a _____ and the allocation may be based on the _______ or _____.
49. What is a binary semaphore ? What is a counting semaphore ?
50. A counting semaphore is like having multiple keys to a house. Justify.
51. Define Mutex. Why is it required ?
52. Why is disabling the scheduler to achieve mutual exclusion an excellent idea but a very dangerous idea ?
53. Why should disabling the interrupts to achieve mutual exclusion be used with caution ?
54. Explain the steps in test-and-set operation to achieve mutual exclusion.
55. Why should the mutex be regarded as a special binary semaphore ? Explain the features that make it so.
56. Which of the two, semaphore or mutex, supports priority inheritance ?
57. When two or more resources are waiting for a very long time for a resource held by another task , a ________ occurs.
58. Watchdog timers are used to avoid __________.
59. How are mailboxes and message queue related ?
60. Can an ISR deposit a message into a mailbox ?
61. What happens at the time of queue creation ?
62. Show how message queues help in one-way, two-way and broadcast communication.
63. A bit in the event register can be used to represent the ________ of an event.
64. The meaning of a 1 or a 0 in an event register is decided by a protocol.
65. Task-to-task or ISR-to-task data transfer can take place using ___________.
66. What is a signal ? Why is its use discouraged ?
67. What is the use of a timer ? Explain.
68. __________ ____________ problem arises when a high priority task has to wait while a low priority task executes. How is it overcome ?
69. What is priority inheritance ? Explain through an example.
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