Question

State whether you consider the following statements to be TRUE or FALSE. Justify your answer in each case.

(a) A hard real –time application is made up of only hard real-time tasks.

(b) Every safety-critical real-time system has a fail-safe state.

(c) A deadline constraint between two stimuli can be considered to be behavioral constraint on the environment of the system.

(d) Hardware fault-tolerance techniques can easily be adapted to provide software faulttolerance

(e) A good algorithm for scheduling hard real-time tasks must to complete each task in the shortest time possible

. (f) All hard real-time systems are safety-critical in nature.

Answer 1

Ans a) False-  A hard real‐time application may also contain several non‐real‐time task such as logging activities etc.

Ans b) False- Having fail‐safe states in safety‐critical real‐time systems is meaningless because failure of a
safety‐criticalsystem can lead to loss of lives,
cause damage, etc. Eg :- a navigation system on‐board an aircraft

Ans c) True- It is a behavioral constraint since the constraint is imposed on the second stimulus event.

Ans d) False- Hardware fault‐tolerance is usually achieved using redundancy techniques. However, the property of statistical correlation of failures for
software renders the technique ineffective.

Ans e) False- A scheduling algorithm for hard real-time tasks is only concerned with completing the tasks before the deadlines.

Ans f) False - Not all hard real-time systems are safety- critical in nature.