This document provides an introduction to real-time operating systems (RTOS). It defines an RTOS as an operating system designed to operate in constrained environments with limited memory and processing power, and often needs to provide services within a defined time period. The key components of an RTOS include its kernel, board support package (BSP), tasks, task control blocks, memory management, timers, and inter-process communication (IPC). RTOS kernels are either monolithic or microkernel in structure. BSPs make RTOSs specific to a target processor. Tasks are the basic units of execution and are scheduled deterministically.

1. Introduction to RTOS
Yong Heui Cho @ Mokwon University
Most of slides are referred to and all credits should go to:
[1] Swetanka Kumar Mishra & Kirti Chawla, RTOS Design & Implementation,
slideshare, 2014.

2. 2
Smart Device Structure
8. Introduction to IoT
9. Smart Device RF & Antennas
10. Introduction to RTOS
11. Introduction to Bluetooth

3. 3
RTOS
• Real-Time Operating System
• A variant of OS that operates in
constrained environment in which
computer memory and processing power is
limited
– Moreover they often need to provide their
services in definite amount of time.
• Hard, Soft & Firm RTOS
• Example RTOS: VxWorks, pSOS, Nucleus,
RTLinux
□ Courtesy to Mishra & Chawla, RTOS Design & Implementation, slideshare.

4. 4
Types of RTOS

5. 5
Structure of RTOS
Custom-Hardware
RTOS-kernel
Applications
BSP
□ Courtesy to Mishra & Chawla, RTOS Design & Implementation, slideshare.

6. 6
Component of RTOS
• The most important component of
RTOS is its kernel.
– Monolithic & Microkernel
• BSP or Board Support Package makes an
RTOS target-specific.
– It’s a processor specific code onto
(processor) which we like to have our RTOS
running.
□ Courtesy to Mishra & Chawla, RTOS Design & Implementation, slideshare.

7. 7
RTOS Kernel
□ Courtesy to Mishra & Chawla, RTOS Design & Implementation, slideshare.

8. 8
Task
• A task is basic unit of execution in
RTOS.
• RTOS scheduler needs to be
deterministic ~ O(1) or O(n).
• Scheduling policies that are available in
a RTOS are:
– Clock driven
– Priority driven
□ Courtesy to Mishra & Chawla, RTOS Design & Implementation, slideshare.

9. 9
Task Control Block
.
.
TID
SAVED_TASK_STATE
Resource 1 (signals)
Resource 2 (events)
Resource 3 (shared memory)
System Variables
□ Courtesy to Mishra & Chawla, RTOS Design & Implementation, slideshare.

10. 10
Memory
• Memory is premium in environments
where RTOS work.
• Supports Virtual Memory (MMU:
Memory Management Unit) and
Memory Protection (MPU) models.
• User space and Kernel space memory.
□ Courtesy to Mishra & Chawla, RTOS Design & Implementation, slideshare.

11. 11
Virtual Memory Concept
Physical Address Virtual AddressM
.
.
.
.
.
PHY1 VIRT1
PHY2 VIRT2
PHY3 VIRT3
PHY4 VIRT4
□ Courtesy to Mishra & Chawla, RTOS Design & Implementation, slideshare.

12. 12
Timer
• Timer is SW entity derived from
hardware clock.
• Timer provides mechanism to introduce
task-delays and/or to help synchronize
and provide time off-course.
• Watchdog Timers, Programmable
Timers
□ Courtesy to Mishra & Chawla, RTOS Design & Implementation, slideshare.

13. 13
Inter-Process Com.
• Most of the time tasks cannot run in
isolation. They require to talk to each
other.
• Synchronization, Protection and
Sharing are goals of IPC.
□ Courtesy to Mishra & Chawla, RTOS Design & Implementation, slideshare.

14. 14
Device Driver
Client Drivers
Protocol Layers
Host Controller Drivers
Hardware
□ Courtesy to Mishra & Chawla, RTOS Design & Implementation, slideshare.