RTOS-RTXC

RTXC Real Time eXecutive in C -a real time OS

- By Vamshi Krishna D

Contents • • • • • • • • • • • • • • • • • •

What is RTOS Scheduling Methods Designs of RTOS -Event Driven & Time sharing Task & Its states. READY LIST Inter task communication and sharing RTXC Overview RTXC Features Rules of RTXC RTXC Tasks Semaphores Queues Resources Timers Interrupt service Routine Introduction to RTXCGen Introduction to RTXCBug Glossary of Terms

What is RTOS •

A real-time operating system (RTOS) is a multitasking

operating system intended for real-time applications. Such applications include embedded systems and scientific research equipment . • An RTOS provides facilities which, if used properly, guarantee deadlines can be met generally (soft real-time) or deterministically (hard real-time). • Scheduling multiple tasks(jobs) to meet deadlines(wrt User) is caller Real time . • Key factors in an RTOS are therefore a minimal interrupt latency and a minimal thread switching latency. •

The real key for designing RTOS is designing the

scheduler

Scheduling Methods • Scheduling

methods

An RTOS will typically use specialized scheduling algorithms in order to provide the real-time developer with the tools necessary to produce deterministic behavior in the final system. • Two basic designs exist: •

•

Event-driven (priority scheduling) designs switch tasks only when an event of higher priority needs service, called preemptive priority.

•

Time-sharing designs switch tasks on a clock interrupt, and on events, called round robin.

•

Newer RTOSes almost invariably implement time-sharing

scheduling with priority driven pre-emptive scheduling.

Event-Driven designs •

Priority-based scheduling: The static priority :A task is given a priority at the time it is created, and it keeps this priority during the whole lifetime. The scheduler is very simple, because it looks at all wait queues at each priority level, and starts the task with the highest priority to run. Dynamic priority:The scheduler becomes more complex because it has to calculate task’s priority on-line, based on dynamically changing parameters. Earliest-deadline-first (EDF) --- A task with a closer deadline gets a higher scheduling priority. Rate-monotonic scheduling :A task gets a higher priority if it has to run more frequently.This is a common approach in case that all tasks are periodic. So, a task that has to run every n milliseconds gets a higher priority than a task that runs every m milliseconds when n