RTOS Scheduling

7/30/2019 RTOS Scheduling

1/21

Scheduling In RTOS

REMOVED


2/21

Real-Time Operating System

Focus on the real-time aspects of operating

systems.

Provide a predictable service to the

application tasks

the temporal properties of the system can be

statically analyzed


3/21

Classification of Scheduling

Algorithms


4/21

Scheduling Algorithm

Rate Monotonic (RM) Algorithm

a dynamic preemptive algorithm

assigning priorities to tasks according to the

frequency or rate of the tasks.

higher rate task has a higher priority

optimal for single processor systems


5/21


Least Laxity (LL) Algorithm



laxity (the difference between the deadline

interval and the computation time)

shorter laxity task has higher priorityoptimal for single processor systems


6/21


Earliest-Deadline-First (EDF) Algorithm



deadline

earlier deadline task has a higher priority

optimal for single processor systems


7/21


Priority Ceiling Protocol

used to schedule a set of periodic tasks that

have exclusive access to common resourcesprotected by semaphores

a task will be blocked once at most by the

duration of a single critical section

solve the problems of chained blocking and

deadlocks


8/21

Rate Monotonic Analysis

a collection of quantitative methods and

algorithms

used to specify, understand, analyze and

predict the timing behavior of real-time

software systems

save system resources and developmenttime


9/21


important factors The worst-case execution time of each

thread of control

the minimum amount of time between

successive invocations of each thread

the priority levels associated with the

execution of each thread

sources of overhead such as those due to an

operating system


10/21


important factors (cont) Dealys due to interprocess communication

and synchronization

allocation of threads of control to physical

resources such as CPUs, buses and

networks


11/21

What is RapidRMA

RapidRMA: Hard real-time systems, such as flight control,

automotive control, medical device, simulator, and

telemetry systems

Soft real-time systems, such as networks and telecom

RapidRMA provides sophisticated tools for

designing new systems and for evaluating existing

systems

RapidRMA can also save data as tabular reports

for off-line analysis or transfer into a spreadsheet


12/21

When do you use RapidRMA?

During system design, to validate the timing

requirements of a new system before coding

When prototyping, to identify potentialarchitecture problems and revalidate timing

requirements

On existing systems, to pinpoint potential timing

problems and bottlenecks in the architecture

Iteratively throughout the life of the system,

whenever new timing data is available


13/21

RapidRMA Algorithms

RapidRMA is based on the following Analysis

and Scheduling algorithms:

Rate Monotonic

Deadline Monotonic

Earliest Deadline First

Cyclic Executive

HKL (Harbour, Klein, and Lehocsky)

SGL (Sun, Gardener, and Liu)


14/21

RapidRMA Algorithms

RMA addresses the timingrequirements of tasks,

not the taskfunctionality

RapidRMA software modules implement bothcommonly used and new scheduling algorithms

and access control protocols for Periodictask handling

Aperiodicjob handling Online and offline scheduling ofimprecise

computations

Many other recently developed techniques


15/21

LynxOS

Unix-compatible

Multi-processor

Multi-thread

Real-time


16/21

LynxOS scheduling

Hard-real-time scheduling

256 global user-thread priority levels

Round-Robin, Quantum, and FIFO policies

at each of 256 priorities

Fast context switching and short blocking

times

Preemptive RTOS kernel

Priority inheritance through semaphores


17/21

OSE Realtime Kernel

Categories of Processes

Static Processes

created at system start by the kernel

exist at all times, the life time of the system

Dynamic Processes

created and killed freely during run-time enable the system to run multiple instances of the

same code


18/21

OSE Realtime Kernel

States of the processes

Running

only one process can be in this state

Ready

placed in a ready queue

Waiting waiting for some event to occur


19/21

OSE Realtime Kernel

Scheduling Principles

Pre-emptive

Cyclic

Priority Based

Round Robin


20/21

OSE Realtime Kernel

Processes Types

Interrupt Processes

Timer Interrupt Processes

Prioritized Processes

Background Processes

Phantom Processes


21/21

Conclusion

OSE is designed to satisfy requirements for

non-stop operation and distribution over

many CPUs. It provides the platform

necessary for seamless operation of fault-

tolerant and safety-critical systems.

LynxOS can control the processes

scheduling more effeciently, processes can

execute at their assigned priorities

regardless of other activities in the system.

RTOS Scheduling

Documents

Transcript of RTOS Scheduling