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Timing Constraints , Tardiness and Timing Guarantee for Hard Real Time System

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need of timing guarantee for hard real time systemExplanation of Timing Constraints , Tardiness,
Why hard real time system require timing guarantees?,
Real Time System Notes | Sixth Semester,
BSc.CSIT | Tribhuvan University (TU)

Timing Constraints
A constraint imposed on the timing behavior of a job is known as timing constraint. Timing constraint of a job can be specified in terms of its release time (instance of time at which the job becomes available for execution) and relative or absolute deadline (instant of time by which execution is required to be completed). Some complex timing constraint can’t be specified conveniently in terms of release time and deadlines.


  • Tardiness of a job measures how late it completes respective to its deadline.
  • Tardiness is zero if job completes at or before deadline otherwise if the job is late, tardiness is equal to the difference between its completion time (time instant at which completes execution) and its deadline

Why does a hard real time system require timing guarantees?
Lets make clear that why any hard real time system require or need timing guarantees by following examples;

  • Control law computation job of a flight controller must be completed in time so that its command can be issued in time otherwise the plane controlled by it may become oscillatory or even unstable and uncontrollable.
  • Critical information system must never be down for more than a minute. Recovery and reconfiguration of database servers and network connection in the system must complete within a few seconds. Otherwise there could be loss of critical data under very less time period also.
  • Whenever it is not possible to prove without doubt that a few timing constraints violation will not jeopardize the safety of users or availability of some initial infrastructure, we take the safe approach and insist on satisfaction of all timing constraints even though the requirement may be unnecessarily stringent.
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