Page 57 - DCAP608_REAL TIME SYSTEMS

Real Time Systems

Notes may make sense to sacrifice the less critical jobs so that the more critical jobs can meet their
deadline. In a flight control and management system, the job that controls the flight of the
aircraft is more critical than the navigation job that determines the current position relative to
the chosen course.

Notes Laxity Type and Function
The laxity type of a job indicates whether its timing constraints are soft or hard. The laxity
type of a job is sometimes supplemented by a usefulness function. In hard real-time
systems solid steps are given in figure further. The usefulness of the result becomes zero
or negative as soon as the job is tardy. It is then better not to execute the job than to execute
it and complete it late. Release a bomb on the target. The dashed and dotted lines show
two other usefulness functions dotted, e.g. transaction on Point of sales system, more
delay more unsatisfied customer. Eventually usefulness is zero when customer leaves.
Dashed, usefulness is decreasing more rapidly and becomes negative, Stock exchange, late
results will be misleading. Usefulness function is shown below:

Figure 5.1: Usefulness Function

Source: ansari.szabist-isb.edu.pk/RTS/RTS0508.ppt

Self Assessment

Fill in the blanks:
1. Tasks often have ……………… dependencies specified among themselves, ………………
dependencies are more common.

2. Tasks might become ……………… for several reasons.
3. A common form of dependency arises when one task needs the results of another task to
proceed with its ………………

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