> For the complete documentation index, see [llms.txt](https://mwx.twelite.info/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mwx.twelite.info/latest_en/api-reference/sys_callbacks/wakeup.md).

# wakeup()

Called before `loop()` when waking up from sleep, and includes procedures for initialization after returning from sleep and for branching processing depending on the state of return.

{% hint style="info" %}
If there is no processing in `loop()` but only reading of sensors, etc., sleep can be performed again in this function.
{% endhint %}

{% hint style="info" %}
This callback function definition is optional.
{% endhint %}