Real Time Operating system (RTOS) - Embedded systems

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 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.

 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.

 “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.

 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.

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

 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

 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.

 Task management
 Scheduling
 Resource Allocation
 Interrupt Handling

 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.

Real Time Operating system (RTOS) - Embedded systems

 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.

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

 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.

 Clock Driven Scheduling
 Round Robin Scheduling
 Priority Scheduling

 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.

 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.

 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

 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.

 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.

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

 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.

 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.

 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/

Real Time Operating system (RTOS) - Embedded systems

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