add support for MQTT

This commit adds support for MQTT in the cloud module.

Signed-off-by: Simen S. Røstad <simen.rostad@nordicsemi.no>

Author: simensrostad

CMakeLists.txt

@@ -4,7 +4,4 @@
 # This CMake file is picked by the Zephyr build system because it is defined
 # as the module CMake entry point (see zephyr/module.yml).
 
-
-zephyr_include_directories(include)
-
-add_subdirectory(drivers)
+add_subdirectory(examples/modules/cloud)

Kconfig

@@ -0,0 +1,8 @@
+# Copyright (c) 2025 Nordic Semiconductor ASA
+# SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
+#
+# This Kconfig file is picked by the Zephyr build system because it is defined
+# as the module Kconfig entry point (see zephyr/module.yml). You can browse
+# module options by going to Zephyr -> Modules in Kconfig.
+
+rsource "examples/modules/cloud/Kconfig.cloud_mqtt"

app/CMakeLists.txt

@@ -15,7 +15,10 @@ target_include_directories(app PRIVATE src/common)
 # Add main application source
 target_sources(app PRIVATE src/main.c)
 
-# Include mandatory module source folders
+# Module source folders
+add_subdirectory(src/modules/location)
+add_subdirectory(src/modules/cloud)
+add_subdirectory(src/modules/fota)
 add_subdirectory(src/modules/network)
 add_subdirectory(src/modules/button)
 add_subdirectory(src/cbor)
@@ -24,6 +27,3 @@ add_subdirectory(src/cbor)
 add_subdirectory_ifdef(CONFIG_APP_POWER src/modules/power)
 add_subdirectory_ifdef(CONFIG_APP_ENVIRONMENTAL src/modules/environmental)
 add_subdirectory_ifdef(CONFIG_APP_LED src/modules/led)
-add_subdirectory_ifdef(CONFIG_APP_LOCATION src/modules/location)
-add_subdirectory_ifdef(CONFIG_APP_CLOUD src/modules/cloud)
-add_subdirectory_ifdef(CONFIG_APP_FOTA src/modules/fota)

app/src/modules/cloud/CMakeLists.txt

@@ -4,7 +4,7 @@
 # SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
 #
 
-target_sources(app PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/cloud.c)
+target_sources_ifdef(CONFIG_APP_CLOUD app PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/cloud.c)
 target_sources_ifdef(CONFIG_APP_CLOUD_SHELL app PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/cloud_shell.c)
 target_include_directories(app PRIVATE .)
 

app/src/modules/fota/CMakeLists.txt

@@ -4,5 +4,5 @@
 # SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
 #
 
-target_sources(app PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/fota.c)
+target_sources_ifdef(CONFIG_APP_FOTA app PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/fota.c)
 target_include_directories(app PRIVATE .)

app/src/modules/location/CMakeLists.txt

@@ -4,5 +4,5 @@
 # SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
 #
 
-target_sources(app PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/location.c)
+target_sources_ifdef(CONFIG_APP_LOCATION app PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/location.c)
 target_include_directories(app PRIVATE .)

docs/common/customization.md

@@ -424,3 +424,66 @@ The dummy module is now ready to use. It provides the following functionality:
 To test the module, send a `DUMMY_SAMPLE_REQUEST` message to its zbus channel. The module will respond with a `DUMMY_SAMPLE_RESPONSE` containing the incremented counter value.
 
 This dummy module serves as a template that you can extend to implement more complex functionality. You can add additional message types, state variables, and processing logic as needed for your specific use case.
+
+## Using a different Cloud
+
+To connect to a generic MQTT server using the Asset Tracker Template, you can use the example cloud module provided under `examples/modules/cloud`. This module replaces the default nRF Cloud CoAP-based cloud integration with a flexible MQTT client implementation.
+
+### Overview
+
+- **Location and FOTA**: These features are deactivated when using the example MQTT module because they depend on nRF Cloud CoAP.
+- **FOTA and LOCATION channels**: The MQTT cloud module provides stub channel declarations for FOTA and LOCATION to avoid build errors. You can implement your own FOTA and LOCATION modules based on your chosen cloud service if needed.
+- **MQTT Client default configurations:**
+
+    - **Broker hostname:** mqtt.nordicsemi.academy
+    - **Port:** 8883
+    - **TLS:** Yes
+    - **Authentication:** Server only
+    - **CA:** modules/examples/cloud/creds/ca-cert.pem
+    - **Device ID** IMEI
+    - **Subscribed topic** imei/att-pub-topic
+    - **Publishing toptic** imei/att-sub-topic
+
+The default configuration does not require/enable mutual authentication meaning that the device does not authenticate itself to the server.
+That would require a device certificate/private key pair. However, the server is authenticated using the server certificate `ca-cert.pem`located in the module example folder.
+
+Configurations for the MQTT stack can be set in the `overlay-mqtt.conf` file and Kconfig options defined in `examples/modules/cloud/Kconfig.cloud_mqtt`.
+
+### How to use the MQTT Cloud Example
+
+1. **Build and flash with the MQTT overlay**
+
+   In the template's `app` folder, run:
+
+   ```sh
+   west build -p -b thingy91x/nrf9151/ns -- -DEXTRA_CONF_FILE="$(PWD)/../examples/modules/cloud/overlay-mqtt.conf" && west flash --erase --skip-rebuild
+   ```
+
+2. Observe that the device connects to the broker
+
+3. **Test using shell commands**
+
+4. **Shell module for testing**
+
+   The MQTT cloud module includes a shell module/commands for testing cloud publishing much like the default CoAP configuration.
+   To implement custom cloud shell commands this module can be used `examples/modules/cloud/cloud_mqtt_shell.c`
+
+### **Module State Machine**
+
+The cloud MQTT module uses a state machine to manage connection and reconnection logic. Below is a mermaid diagram representing the module's states:
+
+   ```mermaid
+   stateDiagram-v2
+       [*] --> STATE_RUNNING
+       STATE_RUNNING --> STATE_DISCONNECTED : NETWORK_DISCONNECTED
+       STATE_DISCONNECTED --> STATE_CONNECTING : NETWORK_CONNECTED
+       STATE_CONNECTING --> STATE_CONNECTING_ATTEMPT
+       STATE_CONNECTING_ATTEMPT --> STATE_CONNECTING_BACKOFF : CLOUD_CONN_FAILED
+       STATE_CONNECTING_BACKOFF --> STATE_CONNECTING_ATTEMPT : CLOUD_BACKOFF_EXPIRED
+       STATE_CONNECTING_ATTEMPT --> STATE_CONNECTED : CLOUD_CONN_SUCCESS
+       STATE_CONNECTED --> STATE_DISCONNECTED : NETWORK_DISCONNECTED
+       STATE_CONNECTED --> STATE_CONNECTED : PAYLOAD_CHAN / send_data()
+       STATE_CONNECTED --> STATE_CONNECTED : <module>_SAMPLE_RESPONSE / send_<module>_data()
+       STATE_CONNECTED --> STATE_CONNECTED : NETWORK_CONNECTED / (noop)
+       STATE_CONNECTED --> STATE_DISCONNECTED : exit / mqtt_helper_disconnect()
+   ```

examples/modules/cloud/CMakeLists.txt

@@ -0,0 +1,21 @@
+#
+# Copyright (c) 2025 Nordic Semiconductor ASA
+#
+# SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
+#
+
+# Prevent this example module from being included in images that doesn't enable the MQTT cloud module
+if (NOT CONFIG_APP_CLOUD_MQTT)
+	return()
+endif()
+
+add_subdirectory(creds)
+
+zephyr_sources(${CMAKE_CURRENT_SOURCE_DIR}/cloud_mqtt.c)
+zephyr_sources(${CMAKE_CURRENT_SOURCE_DIR}/cloud_mqtt_shell.c)
+
+if (CONFIG_NRF_CLOUD_COAP_SEC_TAG GREATER_EQUAL 2147483648 AND CONFIG_NRF_CLOUD_COAP_SEC_TAG LESS_EQUAL 2147483667)
+	message(WARNING "CONFIG_NRF_CLOUD_COAP_SEC_TAG is set to a developer security tag. "
+			"TLS traffic can now be decrypted with Nordic tools. "
+			"This should only be used during development and testing.")
+endif()

examples/modules/cloud/Kconfig.cloud_mqtt

@@ -0,0 +1,142 @@
+#
+# Copyright (c) 2025 Nordic Semiconductor
+#
+# SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
+#
+
+menuconfig APP_CLOUD_MQTT
+	bool "Cloud module"
+	depends on MQTT_HELPER
+	depends on HW_ID_LIBRARY
+
+if APP_CLOUD_MQTT
+
+config APP_CLOUD_MQTT_HOSTNAME
+	string "MQTT broker hostname"
+	default "mqtt.nordicsemi.academy"
+	help
+	  Hostname of the MQTT broker to connect to.
+
+config APP_CLOD_MQTT_TOPIC_SIZE_MAX
+	int "MQTT topic size"
+	default 64
+	help
+	  Maximum size of the MQTT topics used for publishing and subscribing to messages.
+
+config APP_CLOUD_MQTT_PUB_TOPIC
+	string "MQTT publish topic"
+	default "att-pub-topic"
+	help
+	  Topic used for publishing messages to the MQTT broker.
+
+config APP_CLOUD_MQTT_SUB_TOPIC
+	string "MQTT subscribe topic"
+	default "att-sub-topic"
+	help
+	  Topic used for subscribing to messages from the MQTT broker.
+
+config APP_CLOUD_MQTT_SEC_TAG
+	int "MQTT security tag"
+	default 888
+	help
+	  Security tag used to store the MQTT credentials in the modem using Modem Key Management API
+
+config APP_CLOUD_MQTT_SHELL
+	bool "Enable cloud shell"
+	default y if SHELL
+	help
+	  Enable cloud shell commands.
+
+config APP_CLOUD_PAYLOAD_BUFFER_MAX_SIZE
+	int "Payload maximum buffer size"
+	default 128
+	help
+	  Maximum size of the buffer sent over the payload channel when sending RAW JSON messages
+	  to the cloud.
+
+config APP_CLOUD_SHADOW_RESPONSE_BUFFER_MAX_SIZE
+	int "Payload maximum buffer size"
+	default 512
+	help
+	  Maximum size of the buffer used to receive shadow responses from the cloud.
+
+config APP_CLOUD_BACKOFF_INITIAL_SECONDS
+	int "Reconnection backoff time in seconds"
+	default 60
+	help
+	  Time in between reconnection attempts to the MQTT server.
+	  The timer starts after the last failed attempt.
+
+choice APP_CLOUD_BACKOFF_TYPE
+	prompt "Reconnection backoff type"
+	default APP_CLOUD_BACKOFF_TYPE_LINEAR
+
+config APP_CLOUD_BACKOFF_TYPE_EXPONENTIAL
+	bool "Exponential backoff"
+	help
+	  Exponential backoff doubles the reconnection timeout after each failed attempt.
+	  The maximum reconnection timeout is defined by APP_CLOUD_BACKOFF_MAX_SECONDS.
+
+config APP_CLOUD_BACKOFF_TYPE_LINEAR
+	bool "Linear backoff"
+	help
+	  Linear backoff adds a fixed amount of time to the reconnection timeout after each failed attempt,
+	  as defined by APP_CLOUD_BACKOFF_LINEAR_INCREMENT_SECONDS.
+
+config APP_CLOUD_BACKOFF_TYPE_NONE
+	bool "No backoff"
+	help
+	  No backoff means that the reconnection timeout is constant at the value defined by
+	  APP_CLOUD_BACKOFF_INITIAL_SECONDS.
+
+endchoice
+
+config APP_CLOUD_BACKOFF_LINEAR_INCREMENT_SECONDS
+	int "Reconnection backoff time increment"
+	default 60
+	help
+	  Time added to the reconnection timeout after each failed attempt in seconds.
+	  The maximum reconnection timeout is defined by APP_CLOUD_BACKOFF_MAX_SECONDS.
+
+config APP_CLOUD_BACKOFF_MAX_SECONDS
+	int "Maximum reconnection timeout"
+	default 3600
+	help
+	  Maximum reconnection backoff value in seconds.
+
+config APP_CLOUD_THREAD_STACK_SIZE
+	int "Thread stack size"
+	default 3328
+
+config APP_CLOUD_MESSAGE_QUEUE_SIZE
+	int "Message queue size"
+	default 5
+	help
+	  ZBus subscriber message queue size.
+
+config APP_CLOUD_WATCHDOG_TIMEOUT_SECONDS
+	int "Watchdog timeout"
+	default 180
+	help
+	  Timeout in seconds for the cloud module watchdog.
+	  The timeout given in this option covers both:
+	    * Waiting for an incoming message in zbus_sub_wait_msg().
+	    * Time spent processing the message, defined by
+	      CONFIG_APP_CLOUD_MSG_PROCESSING_TIMEOUT_SECONDS.
+	  Ensure that this value exceeds CONFIG_APP_CLOUD_MSG_PROCESSING_TIMEOUT_SECONDS.
+	  A small difference between the two can mean more frequent watchdog feeds, which increases
+	  power consumption.
+
+
+config APP_CLOUD_MSG_PROCESSING_TIMEOUT_SECONDS
+	int "Maximum message processing time"
+	default 120
+	help
+	  Maximum time allowed for processing a single message in the module's state machine.
+	  The value must be smaller than CONFIG_APP_CLOUD_WATCHDOG_TIMEOUT_SECONDS.
+
+module = APP_CLOUD_MQTT
+module-str = Cloud MQTT
+source "subsys/logging/Kconfig.template.log_config"
+
+endif # APP_CLOUD_MQTT