Quiz 1

Question 1

There are two types of real-time systems, what are they?

Answer 1

Hard real-time systems and soft real-time systems

Question 2

What is the difference between hard and soft real-time systems

Answer 2

Hard real-time systems are strictly adherent to deadlines, where timing is absolutely vital.
Soft real-time systems are more forgiving, where occasional timing breaches do not cause critical failure.

The primary difference between the two is based on their tolerance for timing constraints.

Question 3

To coordinate the process of sharing the CPU between multiple tasks, RTOS uses a program called a ________________

Answer 3

Kernel

Question 4

What four things is an RTOS responsible for?

Answer 4

• Task management (scheduling/dispatching)
• Communication between tasks
• Input and output management
• Memory management

Question 5

True or False: An RTOS can run tasks in parallel

Answer 5

False, an RTOS can switch between tasks (run concurrently) but they cannot be run in parallel

Question 6

True or False: Tasks executions are asynchronous to each other

Answer 6

True

Question 7

What is an event?

Answer 7

An event is defined as a change in the signals (hardware) or in the variables (software)

Question 8

What are the two types of events that could occur?

Answer 8

Periodic: An event with a deterministic period
Sporadic: Non-periodic and non-deterministic

Question 9

True or False: The minimum time between sporadic events must be known

Answer 9

True, or else all events may not be captured

Question 10

To detect an event, input signals can be ___________________________ to synchronize real-time events with the program

Answer 10

Sampled periodically

Question 11

If you are given the task execution time, T, and the period, P, how can you calculate the load on the CPU?

Answer 11

Divide the task execution time by the period (L = T/P)

Question 12

If you are given multiple task execution times and periods, how can you calculate the load on the CPU?

Answer 12

Find the sum of all execution times divided by their periods (L = T1/P1 + T2/P2 + … + Tn/Pn)

Question 13

True or False: The necessary condition for a design to be realizable is L > 1

Answer 13

False, L (load on CPU) must be less than or equal to 1

Question 14

True or False: Given the time required to make one pass through the sampling loop, S, and the time required to update the outputs, D, the worst-case response time, R, is:

R <= S + D ~= 2S

Answer 14

True

Question 15

What are the three different types of event detection

Answer 15

• Level detection
• Flag detection
• Edge detection

Question 16

Event detection can be done by _________ in a free-running event loop

Answer 16

Polling

Question 17

What is the formula for polling time in a level-detection free-running event loop

Answer 17

T_poll = T_det + T_srv < T_ep + T_et_2 - T_et_1

Question 18

What is the formula for polling time in a flag-based free-running event loop

Answer 18

T_poll = T_det + T_srv < T_ep

Question 19

What is the condition to detect edges in a free-running event loop

Answer 19

2*T_det + T_srv < T_ep

Question 20

What is the formula for the response time from an event becoming active to the time the response is made in a free-running event loop

Answer 20

T_R = T_poll + T_det + T_srv + T_cir

Question 21

True or False: CPU load can be decreased by using hardware

Answer 21

True

Question 22

An ______________ is a hardware solution for both event detection and changing the program flow

Answer 22

Interrupt

Question 23

What is a problem with using interrupts in multitask systems?

Answer 23

It results in nondeterministic timings and can interrupt a task in the middle of it. To address this, the CPU context must be saved prior to servicing the interrupt (referred to as a context switch)

Question 24

What is a timed event loop?

Answer 24

A programming construct that executes code at regular intervals, ensuring multiple tasks can run at regular intervals

Question 25

True or False: Timed event loops makes scheduling and executing multiple tasks possible

Answer 25

True

Question 26

To not miss an event, the event signal must be sampled with a period, P, that is ________ than the event time

Answer 26

Less

Question 27

The response time of a timed event loop is _________ than a free-running loop

Answer 27

Longer

Question 28

A ________ is needed to coordinate task executions

Answer 28

Kernel

Question 29

To coordinate tasks, either the kernel must ________ tasks or tasks themselves must _________ to share the CPU

Answer 29

Preempt/Interrupt, cooperate

Question 30

What is the difference between a preemptive kernel and a cooperative kernel

Answer 30

Cooperative kernel relies on each task to cooperate in execution, where tasks run until they reach a point where they can voluntarily yield the processor to enable another task to run. Preemptive kernel determines which task should run at any given time and may preempt one task to run another task.

Question 31

What is the condition for proper switch debouncing?

Answer 31

The sampling period must be less than the bounce time (S < B)

Question 32

What is the two-step validation method for switch debouncing?

Answer 32

Read the switch twice in consecutive polling cycles. If the state remains the same, register the press

Question 33

What is mutual exclusion in task scheduling?

Answer 33

Tasks take turns running in different time slices to prevent interference while keeping their original periods

Question 34

When does mutual exclusion NOT help?

Answer 34

When a task is too long to fit in its allocated time slot

Question 35

What is task decomposition?

Answer 35

Splitting a long task into smaller parts so it can run in multiple cycles without blocking other tasks

Question 36

What are the two types of task decomposition?

Answer 36

Co-routines: The task pauses and resumes in multiple cycles State decomposition: The task is broken into steps that run in separate time slices

Question 37

When should task decomposition be used?

Answer 37

When a task’s execution time is longer than the required period of another task

Question 38

Tasks an be decomposed into shorter pieces using a ____________________

Answer 38

State machine

Question 39

What are the most important features of a real-time program?

Answer 39

- Deterministic timing - Predictable - Priority management - Interrupt handling - Concurrency handling