Difference between Delay and Deadline Constraint in Real-time System

Prerequisite – Timing Constraints in Real-time System
1. Delay Constraint :
Delay constraint is the minimum time interval between occurrence of two consecutive events in the real-time system. If an event occurs before the delay constraint, then it is called a delay violation. The time interval between occurrence of two events should be greater than or equal to delay constraint.
If D is the actual time interval between occurrence of two events and d is the delay constraint, then D >= d.

2. Deadline Constraint :
Deadline constraint is the maximum time interval between occurrence of two consecutive events in the real-time system. If an event occurs after the deadline constraint, then the result of event is considered incorrect. The time interval between occurrence of two events should be less than or equal to deadline constraint.
If D is the actual time interval between occurrence of two events and d is the deadline constraint, then D <= d.



Difference between Delay and Deadline Constraint:



DELAY CONSTRAINT DEADLINE CONSTRAINT
It is the minimum time interval between occurrence of two consecutive events. It is the maximum time interval between occurrence of two consecutive events.
It implies that after the occurrence of event E1, event E2 can occur only after the time elapsed is equal to delay constraint. It implies that after the occurrence of event E1, event E2 must occur only before the time elapsed is equal to deadline constraint.
If D is the actual time interval between occurrence of two events and d is the delay constraint, then D >= d. If D is the actual time interval between occurrence of two events and d is the deadline constraint, then D <= d.
Delay violation occurs here if an event occurs before delay constraint. There is no such term as deadline violation if an event occurs after deadline constraint.
The result is not considered incorrect if event occurs before delay constraint. The result is considered incorrect if event occurs after deadline constraint.
Delay Constraint under performance is classified as Response-Response (RR) and Stimulus-Response (SR). Deadline Constraint under performance is classified as Stimulus-Response (SR) and Response-Response (RR).
Delay Constraint under performance is classified as Response-Stimulus (RS) and Stimulus-Stimulus (SS). Deadline Constraint under performance is classified as Stimulus-Stimulus (SS) and Response-Stimulus (RS).

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