This document discusses real-time operating systems (RTOS), which guarantee tasks are completed within specified time constraints. It defines RTOS classifications like hard, firm, and soft based on how missing deadlines affects the system. The key components of an RTOS kernel are described, including scheduling, communication mechanisms, critical regions, timing services, and more. Examples of popular RTOS are provided. The document concludes with defining common RTOS terms used like task, job, release time, execution time, deadline, and response time.

1. RTOS
Introduction –
HARD AND SOFT REAL TIME
SYSTEMS
https://www.youtube.com/watch?v=-
VhJHrnhSrY&list=PLOuGMjEXHeeAcJAO_LFw
vP6N_IEIoUpFm&index=1
Video link

2. Introduction
A real-time operating system (RTOS) is
an operating system that guarantees a certain
capability within a specified time constraint.
Difference between a general purpose and Real
time system is
General purpose OS: Accuracy or performance
oriented
Real Time OS: Time or deadline oriented

3. Examples
LynxOS
OSE
QNX
RTLinux
VxWorks
Windows CE
FREERTOS
POSIX
Symbian
Linux
Ubuntu

4. Components of RTOS kernel

5. Scheduler: Preemptive
scheduler that
guarantees the highest
priority thread is
running.
Communication
Mechanism:
Semaphores, Message
Queues, Queues, etc.
Critical Region
Mechanisms: Mutexes,
Gates, Locks, etc.
Timing Services: Clocks,
Timers, etc.
Power Management:
For low power devices,
power management is
generally part of the
RTOS since it knows the
state of the device.
Memory Management:
Variable-size heaps,
fixed-size heaps, etc.
Peripheral Drivers:
UART, SPI, I2C, etc.
Protocol stacks: BLE,
WiFi, etc.
File System: FatFs, etc.
Device Management:
Exception Handling,
Boot, etc.

6. RTOS
Classifications
These type of RTOS strictly adhere
to the deadline associated with the
tasks. Missing on a deadline can
have catastrophic affects.
Hard RTOS :

7. Firm RTOS :
These type of RTOS are also required to
adhere to the deadlines because missing
a deadline may not cause a catastrophic
affect but could cause undesired affects,
like a huge reduction in quality of a
product which is highly undesired.

8. Soft RTOS :
In these type of RTOS,
missing a deadline is
acceptable.

9. Features of
RTOS
Occupy very less memory
Consume fewer resources
Response times are highly predictable
Unpredictable environment
The Kernel saves the state of the interrupted task
ad then determines which task it should run next.
The Kernel restores the state of the task and
passes control of the CPU for that task.

10. TERMS THAT
WE USE
Task – A set of related tasks that are jointly able to provide
some system functionality.
Job – A job is a small piece of work that can be assigned to a
processor, and that may or may not require resources.
Release time of a job – It's a time of a job at which job
becomes ready for execution.
Execution time of a job: It is time taken by job to finish its
execution.
Deadline of a job: It's time by which a job should finish its
execution.
Maximum It is the allowable response time of a job is called
its relative deadline.
Response time of a job: It is a length of time from the
release time of a job when the instant finishes.
Absolute deadline: This is the relative deadline, which also
includes its release time.

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