Cellular: nRF CoAP Client

The nRF CoAP Client sample demonstrates the communication between a public CoAP server and an nRF91 Series SiP that acts as the CoAP client.

Requirements

The sample supports the following development kits:

Hardware platforms

PCA

Board name

Build target

nRF9161 DK

nrf9161dk_nrf9161

nrf9161dk_nrf9161_ns

nRF9160 DK

PCA10090

nrf9160dk_nrf9160

nrf9160dk_nrf9160_ns

The sample also requires a public CoAP server IP address or URL available on the Internet.

When built for an _ns build target, the sample is configured to compile and run as a non-secure application with Cortex-M Security Extensions enabled. Therefore, it automatically includes Trusted Firmware-M that prepares the required peripherals and secure services to be available for the application.

Overview

The nRF CoAP Client sample performs the following actions:

  1. Connect to the configured public CoAP test server (specified by the Kconfig option CONFIG_COAP_SERVER_HOSTNAME).

  2. Send periodic GET request for a test resource (specified by the Kconfig option CONFIG_COAP_RESOURCE) that is available on the server.

  3. Display the received data about the resource on a terminal emulator.

The public CoAP server used in this sample is Californium CoAP server (coap://californium.eclipseprojects.io:5683). This server runs Eclipse Californium, which is an open source implementation of the CoAP protocol that is targeted at the development and testing of IoT applications. An nRF91 Series DK is used as the CoAP client.

This sample uses the resource obs (Californium observable resource) in the communication between the CoAP client and the public CoAP server. The communication follows the standard request/response pattern and is based on the change in the state of the value of the resource. The sample queries one resource at a time. To configure other resources, use the Kconfig option CONFIG_COAP_RESOURCE.

Configuration

See Configuring your application for information about how to permanently or temporarily change the configuration.

Configuration options

Check and configure the following Kconfig options in the coap_client/prj.conf file:

CONFIG_COAP_RESOURCE - CoAP resource configuration

This option sets the CoAP resource. Default is Californium observable resource.

CONFIG_COAP_SERVER_HOSTNAME - CoAP server hostname

This option sets the CoAP server hostname. Default is californium.eclipseprojects.io.

CONFIG_COAP_SERVER_PORT - CoAP server port

This option sets the port for the CoAP server. Default is 5683.

Sending traces over UART on an nRF91 Series DK

To send modem traces over UART on an nRF91 Series DK, configuration must be added for the UART device in the devicetree and Kconfig. This is done by adding the modem trace UART snippet when building and programming.

Use the Cellular Monitor app for capturing and analyzing modem traces.

Building and running

This sample can be found under samples/cellular/coap_client in the nRF Connect SDK folder structure.

When built as firmware image for the _ns build target, the sample has Cortex-M Security Extensions (CMSE) enabled and separates the firmware between Non-Secure Processing Environment (NSPE) and Secure Processing Environment (SPE). Because of this, it automatically includes the Trusted Firmware-M (TF-M). To read more about CMSE, see Processing environments.

To build the sample with Visual Studio Code, follow the steps listed on the How to build an application page in the nRF Connect for VS Code extension documentation. See Building and programming an application for other building and programming scenarios and Testing and debugging an application for general information about testing and debugging in the nRF Connect SDK.

Testing

After programming the sample to your development kit, complete the following steps to test it:

  1. Connect the kit to the computer using a USB cable. The kit is assigned a COM port (Windows) or ttyACM device (Linux), which is visible in the Device Manager.

  2. Connect to the kit with a terminal emulator (for example, PuTTY). See How to connect with PuTTY for the required settings.

  3. Power on or reset the kit.

  4. Observe that the following output is displayed in the terminal:

    The nRF CoAP client sample started
    
  5. Observe that the discovered IP address of the public CoAP server is displayed on the terminal emulator.

  6. Observe that the nRF91 Series DK sends periodic CoAP GET requests to the configured server for a configured resource after it gets LTE connection.

  7. Observe that the sample either displays the response data received from the server or indicates a timeout on the terminal. For more information on the response codes, see COAP response codes.

Sample output

The sample displays the data in the following format:

CoAP request sent: token 0x9772
CoAP response: code: 0x45, token 0x9772, payload: 15:39:40

Instead of displaying every single CoAP frame content, the sample displays only the essential data. For the above sample output, the information displayed on the terminal conveys the following:

  • code:0x45 - CoAP response code (2.05 - Content), which is constant across responses

  • token 0x9772 - CoAP token, which is unique per request/response pair

  • payload: 15:39:40 - the actual message payload (current time in UTC format) from the resource that is queried in this sample

References

RFC 7252 - The Constrained Application Protocol

Dependencies

This sample uses the following nRF Connect SDK libraries:

It uses the following sdk-nrfxlib library:

It uses the following Zephyr library:

In addition, it uses the following secure firmware component: