27-12-2012, 04:53 PM
Real Time Operating Systems
Real Time Operating.ppt (Size: 249.5 KB / Downloads: 360)
What is Real Time ?
“ Real time in operating systems: The ability of the operating system to provide a required level of service in a bounded response time.”
Soft RTOS…
In a soft real-time system, it is considered undesirable, but not catastrophic, if deadlines are occasionally missed.
Also known as “best effort” systems
Most modern operating systems can serve as the base for a soft real time systems.
Examples:
multimedia transmission and reception,
networking, telecom (cellular) networks,
web sites and services
computer games.
Hard RTOS…
A hard real-time system has time-critical deadlines that must be met; otherwise a catastrophic system failure can occur.
Absolutely, positively, first time every time
Requires formal verification/guarantees of being to always meet its hard deadlines (except for fatal errors).
Examples:
air traffic control
vehicle subsystems control
Nuclear power plant control
Components of an RTOS
Process (task) management
Scheduler
Synchronization mechanism
Interprocess communication (IPC)
Semaphores
Memory management
Interrupt service mechanism
I/O management , H.A.Layer
Development Environments
Communication subsystems (Option)
Board Support Packages (BSP)
Commercial RTOS
Commercial RTOSes different from traditional OS – gives more predictability
Used in the following areas such as:
Embedded Systems or Industrial Control Systems
Parallel and Distributed Systems
E.g. LynxOS, VxWorks, pSoS, QNX , bluecat
Traditionally these systems can be classified into a Uniprocessor, Multiprocessor or Distributed Real-Time OS
Lynx OS
Microkernel design
Means the kernel footprint is small
Only 28 KB in size
The small kernel provides essential services in scheduling, interrupt dispatching and synchronization
The other services are provided by kernel lightweight service modules, called Kernel Plug-Ins (KPIs)
New KPIs can be added to the microkernel and can be configured to support I/O, file systems, TCP/IP, streams and sockets
Can function as a multipurpose UNIX OS
QNX/ Neutrino
POSIX-compliant Unix-like real-time operating system.
Microkernel design – kernel provides essential threads and real-time services
use of a microkernel allows users (developers) to turn off any functionality they do not require without having to change the OS itself.
The system is quite small, fitting in a minimal fashion on a single floppy, and is considered to be both very fast and fairly "complete."
The footprint of microkernel is 12kb.
VxWorks
Created by Wind River.
Current Version: VxWorks 6.0
VxWorks is the most established and most widely deployed device software operating system.
Currently there are more than 300 million devices that are VxWorks enabled.
The core attributes of VxWorks, include high performance, reliability, determinism, low latency and scalability.