.. _mqtt_simple_sample:

nRF9160: Simple MQTT
####################

.. contents::
   :local:
   :depth: 2

The Simple MQTT sample demonstrates how to easily connect an nRF9160 SiP to an MQTT broker and send and receive data.

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

The sample supports the following development kit:

.. table-from-sample-yaml::

Additionally, the sample supports :ref:`qemu_x86`.

.. include:: /includes/tfm.txt

Overview
*********

The sample connects to an MQTT broker and publishes the data it receives on the configured subscribe topic to the configured publish topic.
On a button press event, the sample publishes the configured message to the configured publish topic.
By default, the sample can establish a secure (TLS) connection or a non-secure connection to the configured MQTT broker.
The sample disables power saving modes (PSM and eDRX) so that network events are processed as soon as possible.

Configuration
*************

|config|

Configuration options
=====================

Check and configure the following configuration options for the sample:

.. _CONFIG_MQTT_BROKER_HOSTNAME:

CONFIG_MQTT_BROKER_HOSTNAME - MQTT Broker host name
   This configuration option defines the MQTT Broker host name.

.. _CONFIG_MQTT_CLIENT_ID:

CONFIG_MQTT_CLIENT_ID - MQTT Client ID
   This configuration option specifies the MQTT Client ID.

.. _CONFIG_MQTT_SUB_TOPIC:

CONFIG_MQTT_SUB_TOPIC - MQTT Subscribe topic
   This configuration option sets the MQTT Subscribe topic.

.. _CONFIG_MQTT_PUB_TOPIC:

CONFIG_MQTT_PUB_TOPIC - MQTT Publish topic
   This configuration option sets the MQTT Publish topic.

.. _CONFIG_MQTT_BROKER_PORT:

CONFIG_MQTT_BROKER_PORT - MQTT Broker Port
   This configuration option specifies the port number associated with the MQTT broker.

.. _CONFIG_BUTTON_EVENT_PUBLISH_MSG:

CONFIG_BUTTON_EVENT_PUBLISH_MSG - Button event publish message
   This configuration option specifies the message text which is published on a button press.

.. _CONFIG_BUTTON_EVENT_BTN_NUM:

CONFIG_BUTTON_EVENT_BTN_NUM - Button number for publish
   This configuration option specifies the button number which, when pressed, will publish an MQTT message.

.. _CONFIG_MQTT_RECONNECT_DELAY_S:

CONFIG_MQTT_RECONNECT_DELAY_S - MQTT broker reconnect delay
   This configuration option specifies the delay (in seconds) before attempting to reconnect to the broker.

.. _CONFIG_LTE_CONNECT_RETRY_DELAY_S:

CONFIG_LTE_CONNECT_RETRY_DELAY_S - LTE connection retry delay
   This configuration option specifies delay (in seconds) before attempting to retry LTE connection.

Configuration files
=====================

The sample provides the following predefined configuration files for the following development kits:

* :file:`prj.conf` - For nRF9160 DK
* :file:`prj_qemu_x86.conf` - For x86 Emulation (QEMU)

In addition, the sample provides overlay configuration files, which are used to enable additional features in the sample:

* :file:`overlay-tls.conf` - TLS overlay configuration file for nRF9160 DK
* :file:`overlay-qemu-x86-tls.conf` - TLS overlay configuration file for x86 Emulation (QEMU)
* :file:`overlay-carrier.conf` - LWM2M carrier support for nRF9160 DK

They are located in :file:`samples/nrf9160/mqtt_simple` folder.


To add a specific overlay configuration file to the build, add the ``-- -DOVERLAY_CONFIG=<overlay_config_file>`` flag to your build.

See :ref:`cmake_options` for instructions on how to add this option to your build.
For example, when building on the command line, you can build the sample with the TLS configuration for nRF9160 DK as follows:

  .. code-block:: console

     west build -b nrf9160dk_nrf9160_ns -- -DOVERLAY_CONFIG=overlay-tls.conf

.. note::
   The CA certificate for the default MQTT broker is included in the project and automatically provisioned after boot if the sample is built with the TLS configuration.

Building and running
********************

.. |sample path| replace:: :file:`samples/nrf9160/mqtt_simple`

.. include:: /includes/build_and_run_ns.txt

Testing
=======

|test_sample|

1. |connect_kit|
#. |connect_terminal|
#. Reset your nRF9160 DK.
#. Observe that the sample displays the following information in the terminal::

       The MQTT simple sample started
#. Observe that the development kit connects to the configured MQTT broker (:ref:`CONFIG_MQTT_BROKER_HOSTNAME <CONFIG_MQTT_BROKER_HOSTNAME>`) after it gets the LTE connection.
   At this stage, the development kit is ready to echo the data sent to it on the configured subscribe topic (:ref:`CONFIG_MQTT_SUB_TOPIC <CONFIG_MQTT_SUB_TOPIC>`).
#. Use an MQTT client like `Mosquitto`_ to subscribe to and publish data to the broker.
   Observe that the development kit publishes all the data that you publish to :ref:`CONFIG_MQTT_SUB_TOPIC <CONFIG_MQTT_SUB_TOPIC>` on :ref:`CONFIG_MQTT_PUB_TOPIC <CONFIG_MQTT_PUB_TOPIC>`.

Sample output
=============

The following serial UART output is displayed in the terminal emulator:

.. code-block:: console

      *** Booting Zephyr OS build v2.4.0-ncs1-rc1-6-g45f2d5cf8ea4  ***
      <inf> mqtt_simple: The MQTT simple sample started
      <inf> mqtt_simple: LTE Link Connecting...
      <inf> mqtt_simple: LTE Link Connected!
      <inf> mqtt_simple: Disabling PSM and eDRX
      <inf> mqtt_simple: IPv4 Address found 137.135.83.217
      <inf> mqtt_simple: MQTT client connected
      <inf> mqtt_simple: Subscribing to: my/subscribe/topic len 18
      <inf> mqtt_simple: SUBACK packet id: 1234
      <inf> mqtt_simple: Publishing: Hello from nRF91 MQTT Simple Sample
      <inf> mqtt_simple: to topic: my/publish/topic len: 16
      <inf> mqtt_simple: PUBACK packet id: 51700



Troubleshooting
===============

Public MQTT brokers might be unstable.
If you experience problems connecting to the MQTT broker, try switching to another MQTT broker by changing the value of the :ref:`CONFIG_MQTT_BROKER_HOSTNAME <CONFIG_MQTT_BROKER_HOSTNAME>` configuration option.

.. note::
   If the :ref:`CONFIG_MQTT_BROKER_HOSTNAME <CONFIG_MQTT_BROKER_HOSTNAME>` configuration option is changed and the overlay TLS configuration is used, the included CA certificate must be updated with the CA certificate for
   the newly configurated MQTT broker.


Dependencies
************

This sample uses the following |NCS| library:

* :ref:`lte_lc_readme`

It uses the following `sdk-nrfxlib`_ library:

* :ref:`nrfxlib:nrf_modem`

It uses the following Zephyr library:

* :ref:`MQTT <zephyr:networking_api>`

In addition, it uses the following secure firmware component:

* :ref:`Trusted Firmware-M <ug_tfm>`
