Fixed priority pre-emptive scheduling


Fixed priority pre-emptive scheduling

Fixed priority pre-emptive scheduling is a scheduling system commonly used in real-time systems. With fixed priority pre-emptive scheduling, the scheduler ensures that at any given time, the processor executes the highest priority task of all those tasks that are currently ready to execute.

The pre-emptive scheduler has a clock interrupt task that can provide the scheduler with options to switch after the task has had a given period --- the time slice. This scheduler system has the advantage of making sure no task hogs the processor for any time longer than the time slice. Most RTOS’s have pre-emptive schedulers. Also turning off Time Slicing effectively gives you the non- pre-emptive RTOS.

Pre-emptive scheduling is often differentiated with cooperative scheduling, in which a task can run continuously from start to end without being preempted by other tasks. To have a task switch, the task must explicitly call the scheduler. Cooperative scheduling is used in a few RTOS such as Salvo, or TinyOS.


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