Hardware Reference
In-Depth Information
Feasible schedule
A schedule in which all real-time tasks are executed within their
deadlines and all the other constraints, if any, are met.
Finishing time
The time at which a job finishes executing. It is also called
comple-
tion time
.
Firm task
A task in which each instance must be either guaranteed to complete
within its deadline or entirely rejected.
Guarantee
A schedulability test that verifies whether a task or a set of tasks can
complete within the specified timing constraints.
Hard task
A task whose instances must be a priori guaranteed to complete within
their deadlines.
Hyperperiod
The minimum time interval after which the schedule repeats itself. For
a set of periodic tasks, it is equal to the least common multiple of all the periods.
Idle state
The state in which a task is not active and waits to be activated.
Idle time
Time in which the processor does not execute any task.
Instance
A particular execution of a task. A single job belonging to the sequence of
jobs that characterize a periodic or an aperiodic task.
Interarrival time
The time interval between the activation of two consecutive in-
stances of the same task.
Interrupt
A timing signal that causes the processor to suspend the execution of its
current process and start another process.
Jitter
The difference between the start times (relative to the request times) of two or
more instances of a periodic task. See also
absolute jitter
and
relative jitter
.
Job
A computation in which the operations, in the absence of other activities, are
sequentially executed by the processor until completion.
Kernel
An operating environment that enables a set of tasks to execute concurrently
on a single processor.
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