This document discusses real-time operating systems (RTOS). It begins by defining an RTOS and distinguishing it from traditional operating systems by its ability to respond to external events in a timely manner. It describes the different types of RTOS based on timing constraints. It then covers key RTOS concepts like preemptive priority scheduling, multitasking, inter-task communication, priority inheritance, and memory management. The document also discusses the Nucleus RTOS and whether RTOS will replace traditional operating systems.

1. Real Time Operating System
CCM4320(NETWORK SYSTEMS AND SERVICES) ,
MIDDLESEX UNIVERSITY,LONDON
PREPARED BY
PAWANDEEP KAUR
M00343421
(RTOS)

2. Topics Discussed
1 )REAL TIME OPERATING SYSTEM( INTRODUCTION
AND CONCEPTS)
2)DIFFERENCE BETWEEN REAL-TIME AND
TRADITIONAL OPERATING SYSTEMS
3) NUCLEUS AND ITS FEATURES
4)WILL REAL TIME SYSTEMS REPLACE
TRADITIONAL OS?(FUTURE OF TECHNOLOGY)

3. What is Real-Time Systems(RTOS)?
* Real-time (software) (IEEE 610.12 - 1990):
Response to an external process in a timely manner
when it is performed in actual time and results are
used to control, monitor and respond aptly.
* It manages the hardware resources and hosts
applications like GPOS, with precise timing and high
degree of reliability.

4. Types of RTOS
 Hard Real Time : A timeline constraint shall be satisfied or
the task results in critical failure.
Example: Aircraft, Autopilot plane, and Medical critical care
system etc.
 Firm Real time: Missing a constraint entails unacceptable
quality reductions.
Example : Multimedia applications.
 Soft Real Time: Missed deadline is acceptable and it can be
recovered with no impact on quality.
Example: Online Transaction System, Stock price quotation
system.

6. Pre-emptive Priority Scheduling
The scheduler should be able to pre-empt any task(with the higher
priority to the current) in the system and allocate the resource to
the task that needs it most even at peak load.
Task Priority
Completed Preempted Completed
Time
Task 1
Task 2
Task 3
Task 2 Task4

7. Multitasking
 RTOS supports multitasking in real time
applications.
 Responding in a predictable way to multiple
simultaneous external events (happening in an
uncontrolled way).
 RMS(Rate-Monotonic Scheduling) : An algorithm
with a static-priority scheduling class
 The static priorities are assigned on the basis of the
cycle duration of the job.

8. Reliable and Sufficient Inter Task
Communication Mechanism
 For task synchronization Event Objects and
Semaphore mechanism is used.
1) Event objects are used when synchronization
is required without resource sharing. One or
more task is kept waiting for a specified event to
occur.
2)A semaphore function is a key which needs
to be acquired task to obtain the resource, under
resource sharing environment.
continue…….

9. Inter Task Communication
Task A
Occupied by Task A.
Task B is not authorized
until released by Task A
count=0 count=1
Shared
Resource
Inter-task communication involves sharing of data among tasks
through sharing of memory space, and transmission of data.
Mechanisms
• Message queues
• Pipes
• Remote procedural calls (RPC)
Task B
R1

10. Priority Inheritance
 Priority inheritance is a method for eliminating priority
inversion problem with semaphores, by increasing the priority of
the running process holding the resource to the maximum.
Increasing
High priority task
Attempts to take semaphores and blocks
Priority Enter ready state
Semaphore
Takes Semaphore
Medium priority task preempts Gives Semaphore
low priority task
Low priority task
Time

11. Control of Memory Management
 In RTOS memory access time should be bound(predictable).
 In Hard Real Time systems, static memory allocation system is used at
start up.
 In Soft Real Time Systems, dynamic memory allocation is used without
Virtual Memory and Compaction.
 The Stack Management or kernel stack is the memory management
process in RTOS, where allocation of memory is done using Task
Control Block
 Heap Management: When a task finishes using a memory block it
return memory to heap. It is used by kernel for dynamic memory
allocation.

12. Predefined Short Latencies
 RTOS have accurate and shortest timing of its
system calls for the following behaviors:
• TASK SWITCH OR CONTEXT SWITCH
• INTERRUPT LATENCY
• INTERRUPT DISPATCH LATENCY

13. RT & non-RT systems?
TIME CONSTRAINTS !
PREDICTABILITY !

14. Key Differences
RTOS Traditional OS
Deterministic timing behavior Non-Deterministic
Goals: Predictability and time
constraints.
Goals : Maximum system utilization
and throughput
Pre-emptive Priority Scheduling Round Robin or Time-sharing
Scheduling
Secondary Storage is usually limited
and missing
Secondary Storage are required to run
large processes.

15. few more !
Interrupt latency is bounded Interrupt latency is variant and not
bounded.
Static Memory allocation Dynamic memory allocation
No Virtual Memory and Compaction Virtual Memory and Compaction is an
integral part of Memory Management
Mission critical dedicated applications
and control devices
Large Database and general purpose
applications

16. NUCLEUS RTOS
 By the Embedded Systems Division of Mentor Graphics.
It is an efficient real-time operating system with
1. Database management.
2. USB
3. Networking
4. Multimedia and advanced GUI
 It has evolved into a complete OS comprised of kernel
services, extensions, and APIs
 Support range of electronic products and different types
of microprocessors.

17. Features
Features
*Hard/ Soft real-time performance
* Dynamic task creation/deletion
* Inter-task communication and synchronization via
mailboxes, queues, pipes, semaphores
* Application timers/Event flags
* Full MMU support
* Static/dynamic memory allocation
* Dynamic loading of code
* Familiar APIs including C++, ANSI C, POSIX
* Scales to any target hardware

18. Supports a full range of OS services
 Comprehensive support for networking
 Multiple file formats
 User Interface: Desktop-like control framework,
bitmaps shapes, BSD, 3D interface engine
 802.1x wireless protocols
 Supports various modern input and output devices

19. Broad Hardware Support
 Nucleus RTOS has been ported to hundreds of
different processors across various architectures
including however not limited to

20. Will Real Time Operating Systems
replace Traditional OS ?
HYBRID SOLUTIONS
(THE RTOS AND GPOS ON THE SAME MACHINE,
COMMUNICATING VIA SHARED MEMORY OR OTHER
TECHNIQUES. THE HOST OS IS THE RICH GPOS AND
TARGET OS IS THE DEDICATED RTOS)

21. •Does nBota hsaivce L aallc fkeiantugr eins oTf oGdPaOyS’s l iRkeT sOouSrce
code control systems, back up tools.
•Too expensive to cover vast IT market.
•Complicated to design and harder to use.
•An overqualified RTOS on applications have
negative impacts on time-to-markets.
•Increase in the usage of soft real time based
applications.
• Emergence in the parallel and distributed systems

22. Pawandeep Kaur
M00343421
pp590@live.mdx.ac.uk