.. _nrf-system-off-sample:

nRF5x System Off demo
#####################

Overview
********

This sample can be used for basic power measurement and as an example of
deep sleep on Nordic platforms.  The functional behavior is:

* Busy-wait for 2 seconds
* Sleep for 2 seconds without device power control
* Sleep for 2 seconds after turning UART off, which reduces current draw
  by a couple hundred uA
* Turn the system off after enabling wakeup through a button press

A power monitor will be able to distinguish among these states.

This sample also demonstrates the use of a :c:func:`SYS_INIT()` call to
disable the deep sleep functionality before the kernel starts, which
prevents the board from powering down during initialization of drivers
that use unbounded delays to wait for startup.

RAM Retention
=============

On nRF52 platforms this also can demonstrate RAM retention.  By selecting
``CONFIG_APP_RETENTION=y`` state related to number of boots, number of times
system off was entered, and total uptime since initial power-on are retained
in a checksummed data structure.  The POWER peripheral is configured to keep
the containing RAM section powered while in system-off mode.

Requirements
************

This application uses nRF51 DK or nRF52 DK board for the demo.

Building, Flashing and Running
******************************

.. zephyr-app-commands::
   :zephyr-app: samples/boards/nrf52/system_off
   :board: nrf52dk_nrf52832
   :goals: build flash
   :compact:

Running:

1. Open UART terminal.
2. Power Cycle Device.
3. Device will demonstrate two activity levels which can be measured.
4. Device will demonstrate long sleep at minimal non-off power.
5. Device will turn itself off using deep sleep state 1.  Press Button 1
   to wake the device and restart the application as if it had been
   powered back on.

Sample Output
=================
nRF52 core output
-----------------

.. code-block:: console

   *** Booting Zephyr OS build v2.3.0-rc1-204-g5f2eb85f728d  ***

   nrf52dk_nrf52832 system off demo
   Busy-wait 2 s
   Busy-wait 2 s with UART off
   Sleep 2 s
   Sleep 2 s with UART off
   Entering system off; press BUTTON1 to restart