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Question 1

Periodic task?

Answer 1

For a periodic task the time interval between two subsequent arrivals of the task is guaranteed to be exactly Ti (the periodic parameter)

Question 2

Sporadic task?

Answer 2

For a sporadic task the time interval between two subsequent arrivals of the task is guaranteed to be higher than, or equal to Ti (the periodic parameter)

Question 3

Aperiodic task?

Answer 3

For an aperiodic task there is no guaranteed minimum time interval between two subsequent arrivals of the task.

Question 4

What is systematic time skew?

Answer 4

Systematic skew is a phenomenon relating to periodic task executions, where the actual period becomes longer than the intended one, causing each subsequent task arrival to drift further and further away from its intended arrival time.

Question 5

Why does systematic time skew happen?

Answer 5

Systematic skew is a phenomenon relating to periodic task executions, where the actual period becomes longer than the intended one, causing each subsequent task arrival to drift further and further away from its intended arrival time.

Question 6

How to avoid systematic time skew?

Answer 6

By using an absolute delay statement, specifying an actual time instant on the timeline for the next execution (instead of a delay relative to the current point of execution), the execution time of the calling code does not influence the periodic behaviour. This can be achieved by means of, for example, the AFTER() operation in TinyTimber, where a method’s baseline is used to calculate a time instant on the timeline for the next execution of the method.

Question 7

Describe how
the application programmer instructs the TinyTimber kernel to create a concurrent execution of
a given piece of program code.

Answer 7

To create a concurrent execution the programmer should use the ASYNC operation or one of its associated timing-aware versions (AFTER, SEND, BEFORE), and provide as a parameter an object method identifying the program code to execute concurrently.

Question 8

Critical instant?

Answer 8

A critical instant refers to a task arrival scenario in which the response time of a given task is maximized.

Question 9

Describe how the application programmer instructs the TinyTimber kernel to read the current
value of the system clock.

Answer 9

To read the current value of the system clock the programmer has two options:

The CURRENT OFFSET operation returns the time duration from the current baseline to the current time.

The T SAMPLE operation returns the time duration from a bookmarked baseline to the current baseline. A baseline of an earlier event is bookmarked by means of the T-RESET operation.

Both operations should refer to a common object of type Timer.

Question 10

State the resolution (that is, the length of a time unit) of the system clock in the laboratory system used in the course.

Answer 10

The resolution of the TinyTimber system clock in the laboratory system is 10 μs.

Question 11

Describe the meaning of a false path in the context of worst-case execution-time analysis.

Answer 11

A false path in worst-case execution-time analysis refers to a part of the program code that will never be executed at run-time, for example due to the logical expressions used in an ’if’-statement.

Question 12

Describe the meaning of priority inversion in the context of single-processor scheduling.

Answer 12

By priority inversion we refer to a scenario where a higher-priority task cannot execute because
another task holds a resource that the higher-priority task needs, and a lower-priority task (that
does not use the resource) is able to execute instead.

Question 13

State the major difference between the priority inheritance protocol (PIP) and the deadline inheri-
tance protocol (DIP).

Question 14

SYNC() ?

Question 15

ASYNC() ?

Question 16

AFTER() ?

Question 17

BEFORE() ?

Question 18

SEND() ?

Answer 18

The SEND() operation requests that the specified method should
begin its execution by baseline at the earliest and complete its
execution by deadline at the latest:

Question 19

Describe the
purpose of the baseline in the TinyTimber run-time scheduler.

Answer 19

The baseline of a method execution in the TinyTimber kernel represents the earliest possible start
time of that method execution.

If a method is called with its baseline set to a time later than the
current time of the method call, e.g. by means of an AFTER() or SEND() operation, the execution
of the method will be delayed by the TinyTimber run-time scheduler until the time specified by
the baseline at the earliest.

Question 20

Explain the concept of priority ceiling as used in access-control protocols for critical regions.

Answer 20

A priority ceiling is associated with a shared resource, and represents the priority of the task with highest static priority that may use that resource.

During run-time the access-control protocol makes sure that a task X can enter the critical region of a shared resource only if the priority of task X is higher than all priority ceilings of the resources currently locked by tasks other than task X.

Question 21

State the major difference in the behaviour of the immediate ceiling priority protocol (ICPP) and
the original priority ceiling protocol (PCP).

Answer 21

In the original priority-ceiling protocol (PCP), a task X’s priority is raised only when a higher-priority task tries to acquire a resource that X has locked.

In the immediate ceiling priority
protocol (ICPP), a task X’s priority is immediately raised to the ceiling priority of a resource when X locks the resource.

Question 22

The TinyTimber run-time scheduler takes into account any priority that may be associated with
a method execution. Describe how the application programmer instructs the TinyTimber kernel
that a method execution should be associated with a priority.

Answer 22

Priority is set by specifying a deadline in a BEFORE() or SEND() operation.

TinyTimber uses the earliest-deadline-first (EDF) policy to select among
the ready tasks.

Question 23

Explain why the Traveling Salesman optimization problem cannot be solved by a polynomial-time
non-deterministic Turing machine.

Answer 23

To be solved by a polynomial-time non-deterministic Turing machine the Traveling Salesman problem
must be formulated as a decision problem. That is, a solution to the problem must be verified in
polynomial time with respect to the given Boolean predicate

Question 24

Global..?

Question 25

Dhalls effect and how do we solve the problem?

Answer 25

The solutions to Dhalls effect is the RM-US schedualing test.

Question 26

O bakers test? Formel och vad räknar du ut?

Question 27

Vad betyder partition schedualing (Bin-backing)?

Question 28

Describe the meaning of Dhall’s effect in the context of global multiprocessor scheduling.

State the underlying reason why Dhall’s effect occurs, and also give an example of how the effect
can be avoided.

Answer 28

RM-US

Question 29

RM-US

Question 30

RM-FF