1. Real Time Operating System
Mrs.V.S.Patki,
Assistant Professor,
Department of Electronics Engineering
Walchand Institute of Technology, Solapur
This work is licensed under a Creative Commons Attribution 4.0 International License.

2. Real Time Operating System
Definition
Specialities of RTOs
Why and when to Use RTOs?
Types of RT Systems
Role of Os in RT Systems
Real Time Operating System

3. RTOs Definition Real-time capability Features of a RTOS:
Many embedded systems are real-time (RT) systems and, hence, the OS used in these systems must be real-time operating systems (RTOSs)
Features of a RTOS:
Allows multi-tasking
Scheduling of the tasks with priorities
Synchronization of the resource access
Inter-task communication
Time predictable
Interrupt handling
Real Time Operating System

4. Specialities of RTOS Predictability of timing
The timing behavior of the OS must be predictable
For all services of the OS, there is an upper bound on the execution time
Scheduling policy must be deterministic
The period during which interrupts are disabled must be short (to avoid unpredictable delays in the processing of critical events)
Real Time Operating System

5. Specialities of RTOS OS should manage timing and scheduling Speed:
OS possibly has to be aware of task deadlines; (unless scheduling is done off-line).
Frequently, the OS should provide precise time services with high resolution.
Important if internal processing of the embedded system is linked to an absolute time in the physical environment
Speed:
The OS must be fast
Real Time Operating System

6. Why Use RTOS? Can use drivers that are available with an RTOS
Can focus on developing application code, not on creating or maintaining a scheduling system
Multi-thread support with synchronization
Portability of application code to other CPUs
Resource handling by RTOS
Add new features without affecting higher priority functions
Support for upper layer protocols such as:
TCP/IP, USB, Flash Systems, Web Servers,
CAN protocols, Embedded GUI, SSL, SNMP
Real Time Operating System

7. When to use RTOS?
Necessary when scheduling of multiple processes,ISRs and devices is imp
To monitor the processes that areresp;onse time controlled and event controlled process.
Real Time Operating System

8. Real Time System
A system is said to be Real Time if it is required to complete it’s work & deliver it’s services on time.
Example – Flight Control System
All tasks in that system must execute on time.
Non Example – PC system
Real Time Operating System

9. Hard and Soft Real Time Systems
Hard Real Time System
Failure to meet deadlines is fatal
example : Flight Control System
Soft Real Time System
Late completion of jobs is undesirable but not fatal.
System performance degrades as more & more jobs miss deadlines
Online Databases
Real Time Operating System

10. Hard and Soft Real Time Systems (Operational Definition)
Hard Real Time System
Validation by provably correct procedures or extensive simulation that the system always meets the timings constraints
Soft Real Time System
Demonstration of jobs meeting some statistical constraints suffices.
Example – Multimedia System
25 frames per second on an average
Real Time Operating System

11. Role of an OS in Real Time Systems
Standalone Applications
Often no OS involved
Micro controller based Embedded Systems
Some Real Time Applications are huge & complex
Multiple threads
Complicated Synchronization Requirements
Filesystem / Network / Windowing support
OS primitives reduce the software design time
Real Time Operating System