First-in-First-Out Scheduling (SCHED_FIFO)

The default FIFO scheduler option provides simple pre-emptive FIFO scheduling based on thread priorities. Priority of threads may vary from K_FIFO_PRIOMAX (0, the highest priority) to K_FIFO_PRIOMIN (255, the lowest priority). Within this policy, a thread becomes ready to run after being blocked is always inserted at the end of its priority-ready queue. A running thread is preempted only if a thread of a strictly higher priority is ready to run. A preempted thread is placed at the head of its priority-ready queue, so that it is selected first when the preempting thread completes or is blocked.