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KernelinsideSoftware timers

Updated Jun 2025

FreeRTOS software timers

[More about software timers...]

One-shot timers versus auto-reload timers

There are two types of timer, one-shot timers, and auto-reload timers. Once started, a one-shot timer will execute its callback function only once. It can be manually re-started, but will not automatically re-start itself. Conversely, once started, an auto-reload timer will automatically re-start itself after each execution of its callback function, resulting in periodic callback execution.

The difference in behaviour between a one-shot timer and an auto-reload timer is demonstrated by the timeline in the diagram below. In this diagram, Timer 1 is a one-shot timer that has a period equal to 100, and Timer 2 is an auto-reload timer that has a period equal to 200.

The behaviour of one-shot timers and auto-reload timers

The behaviour of one-shot timers and auto-reload timers