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Real-time Systems (Typical Characteristics (Event-driven, reactive, High…
Real-time Systems
Definition
is a system whose specification includes both
logical
and
temporal
correctness requirements
Logical Correctness
Produces correct outputs
Temporal Correctness
Produces outputs at the right time
Typical Characteristics
Event-driven, reactive
High cost of failure
Concurrency/ multiprogramming
Stand-alone/continuous operation
Reliability/fault-tolerance requriements
Predictable behavior
Hard vs. Soft Real Time
Task
A sequential piece of code
Job
Instance of a task
Release time of a job
The time instant the job becomes ready to execute
Deadline of a job
The time instant by which the job must complete execution
Relative deadline of a job
Deadline - Release time
Response time of a job
Completion time - Release time
RT Computing vs Fast Computing
RT Computing
The objective is to
meet
the
individual timing requirement
of each task
Fast is relative
Worst case, not average case, response time matters
Not speed but
predictability
is the goal
Functional and timing behaviors should be as deterministic as necessary to satisfy system specification
Guarantee the delay is shorter than the upper bound
Predictability is not only hardware or algorithmic issue
Fast Computing
The objective is to
minimize
the
average response time
Cannot necessarily provide predictability
Testing is not the answer