08-02-2013, 10:53 AM
Real-Time Computing
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Embedded computers
Medical control equipment, mobile phones, and vehicle control systems.
Most such embedded systems can also be characterized as real-time systems.
They must usually meet stringent specifications for safety, reliability, limited hardware capacity etc
Characteristics and Challenges of RTS
Real-time systems are computing systems in which the meeting of timing constraints is essential to correctness.
If the system delivers the correct answer, but after a certain deadline, it could be regarded as having failed.
Types of Real-Time Systems
Hard real-time system
A system where “something very bad” happens if the deadline is not met
Examples: control systems for aircraft, nucluear reactors, chemical power plants, jet engines, etc.
Soft real-time system
A system where the performance is degraded below what is generally considered acceptable if the deadline is missed
Example: multimedia system
Issues in Real-Time Computing
Real-time computing deals with all problems in computer architecture, fault-tolerant computing and operating systems are also problems in real-time computing, with the added complexity of having to meet real-time constraints
Real-time computer systems differ from general-purpose systems
They are more specific in their applications
The consequences of their failure are more drastic
Emphasis is placed on meeting task deadlines
Scheduling
Offline scheduling:
The scheduler has complete knowledge of the task set and its constraints.
Online scheduling:
Make their scheduling decisions during run-time.
Deadline:
Is the maximum time within which the task must complete its execution with respect to an event.
Real-time systems are divided into two classes, hard and soft real-time systems