This is a sample project that works both on local etherned (with the external CoAP interface for devices) or via a cellular IoT modem (with the CIoT CoAP interface). The project uses PlatformIO but should build equally well for any supported device in Zephyr. The file zephyr/prj.conf contains the required configure flags for the build.

Run and deploy to the device with pio run --target=upload. Use pio device monitor --raw to view the log.

The ethernet-connected devices uses DTLS with client certificates to authenticate and verify the client connection.

The CIoT devices may elect to use unencrypted UDP for the CoAP service. This makes deployments a bit easier and less resource hungry since they won't need a client certificate, DNS or DHCP support and everything can be configured via Span.

The project is developed on a STM32 F429zi board but it should be relatively easy to modify it to run on any board with ethernet/wifi connectivity or a cellular IoT modem (like the nRF91 from Nordic Semiconductor) as long as it has a rudimentary socket support.