Real Time Operating System Mrs.V.S.Patki, vspatki01@rediffmail.com Assistant Professor, Department of Electronics Engineering Walchand Institute of Technology, Solapur www.witsolapur.org This work is licensed under a Creative Commons Attribution 4.0 International License.

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

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

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

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

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

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

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

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

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

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