02-02-2012, 11:28 AM
Real Time Operating Systems for Networked Embedded Systems
[attachment=17034]
Fire Alarm System
Problem
Hundreds of sensors, each fitted with Low Range Wireless
Sensor information to be logged in a server & appropriate action initiated
Possible Solution
Collaborative Action
Routing
Dynamic – Sensors/controllers may go down
Auto Configurable – No/easy human intervention.
Less Collision/Link Clogging
Less no of intermediate nodes
Fast Response Time
Secure
Real Time System
A system is said to be Real Time if it is required to complete it’s work & deliver it’s services on time.
Example – Flight Control System
All tasks in that system must execute on time.
Non Example – PC system
Hard and Soft Real Time Systems
Hard Real Time System
Failure to meet deadlines is fatal
example : Flight Control System
Soft Real Time System
Late completion of jobs is undesirable but not fatal.
System performance degrades as more & more jobs miss deadlines
Online Databases
Qualitative Definition.
Role of an OS in Real Time Systems
Standalone Applications
Often no OS involved
Micro controller based Embedded Systems
Some Real Time Applications are huge & complex
Multiple threads
Complicated Synchronization Requirements
Filesystem / Network / Windowing support
OS primitives reduce the software design time
Priority Scheduling
Earliest Deadline First (EDF)
Process with earliest deadline given highest priority
Least Slack Time First (LSF)
slack = relative deadline – execution left
Rate Monotonic Scheduling (RMS)
For periodic tasks
Tasks priority inversely proportional to it’s period
