A real-time operating system (RTOS) is an operating system designed for embedded systems where responses need to occur within strict time constraints. An RTOS prioritizes tasks and responds immediately to inputs. There are two types - hard RTOS which must meet deadlines to avoid catastrophic failure, and soft RTOS where occasionally missing deadlines does not cause failure. An RTOS manages tasks, schedules tasks and system resources, and handles interrupts to ensure time-critical applications perform as required.

1. PRESENTED BY:
HARIHARAN.G 17MX105
KALAIYARASAN.D 17MX106
KEERTHANA.R.A 17MX107
KIRUBHANANDHAN.R 17MX108

2.  When we hear the word “Operating
System” the first ones that come to our
mind are Windows, Linux, Ubuntu, MacOS
for computers & Android, iOS for mobiles
and many more .
 A real time operating system is a special
type of OS specifically designed for
Embedded systems.

3.  The basic difference of using a GPOS or
an RTOS lies in the nature of the system –
i.e whether the system is “time critical”
or not.
 Normal operations that we do in a
computer are not time critical & nothing
is going to happen if it takes a few more
seconds to open a file.
 But in applications like Missiles, ABS in
cars, timing is very critical.

4.  “The ability of the operating system to
provide a required level of service in a
bounded response time.”
 Example:
Airbag has to be opened within a
fixed time immediately after the crashing
in order to protect from any injuries.

5.  It responds to inputs immediately (Real-
Time).
 Here the task is completed within a
specified time delay.
 In real life situations like controlling
traffic signal or a nuclear reactor or an
aircraft,The operating system has to
respond quickly.

6.  There are two basic types:
(1) Hard RTOS
(2) Soft RTOS

7.  A hard real-time system has time-critical
deadlines that must be met; otherwise a
catastrophic system failure can occur.
 Examples:
– air traffic control
– vehicle subsystems control
– Nuclear power plant control

8.  In a soft real-time system, deadlines can be
occasionally missed.
 Missing deadlines will not cause any
catastrophic failure.
 Also known as “best effort” systems.
 Examples:
– multimedia player controls
– telecom (cellular) networks switching
– web sites and services
– computer games.

9.  Task management
 Scheduling
 Resource Allocation
 Interrupt Handling

10.  In Real Time Applications, any Process
which takes a specified execution time
and occupies predefined amount of
memory is called as a Task.
 Task management is the process of
managing tasks through its life cycle.

12.  Each task/Process can belong to one and
only one state.
 The Scheduler only operates on the
processes in the Ready state.
 Transitions to and from the Ready queue
are based on the availability of the
resources or the time resource available.

13.  Creating and deleting tasks,
 Controlling task scheduling, and
 Obtaining task information.

14.  Task management provides the following
information about tasks:
– No of tasks
– Resource Requirements
– Release Time
– Execution time
– Deadlines
 RTOS Scheduler uses scheduling
algorithms to organize them.

15.  Clock Driven Scheduling
 Round Robin Scheduling
 Priority Scheduling

16.  Release time/ execution time/deadline
will be known well in advance.
 Schedule can be computed at some
regular time instances.
 Minimal runtime overhead.
 But it might not suitable for all
applications.

17.  Jobs are scheduled in FIFO manner.
 Time quantum given to tasks is not based
on priority.
 Not suitable for precedence constrained
jobs (looping statements).
 Job A can run only after Job B.
 No point in giving time quantum to Job B
before Job A.

18.  Processor is never left idle when there
are ready tasks.
 Processor will be allocated to processes
according to priorities.
 Priorities can be decided either :
• Static - at design time
• Dynamic - at runtime

19.  We know that embedded systems have
limited amount of resources in terms of
memory & CPU power.
 So, it is essential to allocate the available
resources efficiently.
 The same algorithms used for scheduling
are again used for resource allocation.

20.  Interrupt is any external control signal
which disturbs the normal execution of a
system.
 Interrupts cause the processor to
suspend all other operations whatever it
is doing & instead execute the code that
will respond to the event which caused
the interrupt.

21.  VxWorks
 LynxOS
 RTLinux
 Windows CE
 These are some of the popular RTOS
used in the industry.
 VxWorks is the most widely used RTOS.

22.  Real time operating systems are used in
Military, Engineering Application and
Data communication systems.
 Automated Missiles and space satellites
are also powered by RTOS these days.
 In general, any embedded system
application which requires immediate
real-time action uses RTOS.

23.  RTOS can run on applications in any
diverse and challenging environment
conditions also.
 It runs efficiently even on very limited
Hardware resources.
 It consumes less power and memory.
 Kernel size is very small and can fit
limited ROM storage of embedded
systems.

24.  http://www.circuitstoday.com/gpos-versus-rtos-for-
an-embedded-system
 https://www.enotes.com/homework-help/what-some-
examples-real-time-operating-systems-why-276796
 http://www.circuitstoday.com/what-is-real-time-
operating-system-rtos
 https://www.thegeekstuff.com/2012/02/rtos-basics/