Internals of the embeNET demo for NUCLEO-WL55JC board

This document describes the internals of the embeNET demo application running on NUCLEO-WL55JC boards and provides information on how to modify and extend the demo.

How does the demo application work

The demo application uses the embeNET Node C API library to join the network and run two network services:

  • ENMS: embeNET Network Management service that allows to gather information about the network operation from the nodes
  • custom exemplary service, that sends out a simple message every 5 seconds and also reacts to some simple messages

Below is a short explanation of all important steps. Basically the whole application fits into the main function.


The initialization part configures STM32 HAL, system clock, GPIOs and USART1:

/* MCU Configuration--------------------------------------------------------*/
/* Reset of all peripherals, Initializes the Flash interface and the Systick. */
/* Configure the system clock */
/* Initialize all configured peripherals */

Next we configure the logging facility of the embeNET:

LOGGER_SetOutput(logOutputWrapper, NULL);

Next the embeNET stack is initialized:

// Initialize structure to provide Stack with user-defined event handlers
EMBENET_NODE_EventHandlers handlers = {
.onJoined = onJoined,
.onLeft = onLeft,
.onJoinAttempt = onJoinAttempt,
.onDataOnUnregisteredPort = dataOnUregisteredPort,
.onQuickJoinCredentialsObsolete = onQuickJoinCredentialsObsolete
// Initialize network stack

After that the ENMS service is initialized:

// Get hardware ID using 96-bit CPU uid
uint8_t hardwareId[16] = {0x00};
memcpy(hardwareId, (void const*)UID_BASE, 12);
// Initialize ENMS service on its default port. You may specify custom Hardware Identifier and firmware version
if (ENMS_NODE_RESULT_OK == ENMS_NODE_Init(&enmsNode, ENMS_DEFAULT_PORT, hardwareId, 1, 0, 0)) {
printf("ENMS service initialized\n");
} else {
printf("Failed to initialize ENMS service!\n");

In case of root we just start it:


In case of nodes we start the custom demo service and MQTT-SN service:

// Initialize exemplary, user-defined custom service
// Initialize MQTT-SN service
// Additionally tell the ENMS what services are running
(void) ENMS_NODE_RegisterService(&enmsNode, "custom", 1);
(void) ENMS_NODE_RegisterService(&enmsNode, "mqttsn", 1);

Joining the network

In order to join the network the node has to setup the required network configuration:

// embeNET network configuration:
// K1 key, used to authenticate the network node should join and
// PSK - Node's secret key.
// Note that the psk value should be preferably stored in secure memory, or be preloaded using custom bootloader.
EMBENET_NODE_Config config = {
.k1.val = { 0xc0, 0x8b, 0x76, 0x62, 0x77, 0x09, 0x9e, 0x7d, 0x7e, 0x9c, 0x02, 0x22, 0xf1, 0x68, 0xcc, 0x9e },
.psk.val = { 0x46, 0xd7, 0xdc, 0x94, 0xe8, 0xee, 0x74, 0x96, 0xce, 0xaf, 0x54, 0xa3, 0xab, 0x64, 0xcb, 0xeb },
// Make the node join the network

The main loop

The application's main loop consists of a call to:

  • embeNET Node processing function
  • MQTT-SN service process (only needed for polling button status)
/* Infinite loop */
while (1) {
// Periodically call embeNET Node process function.
// Periodically call MQTT-SN service process.

Network join event

Once the node joins the network an event callback will be called. In our demo application this callback simply starts the network services:

static void onJoined(EMBENET_PANID panId, const EMBENET_NODE_QuickJoinCredentials *quickJoinCredentials) {
printf("Joined network with PANID: x%04" PRIx16 "\n", panId);
printf("Starting ENMS service\n");
// Start ENMS Service that provides network-wide telemetry information
EnmsNodeResult enmsStartStatus = ENMS_NODE_Start(&enmsNode);
if (ENMS_NODE_RESULT_OK != enmsStartStatus) {
printf("ENMS service failed to start with status %d\n", (int) enmsStartStatus);
// Start exemplary, user-defined custom service
// Start MQTT-SN demo service

Network leave event

In case when node gets disconnected from the network, another callback is called. In our demo application this callback stops the network services:

static void onLeft(void) {
printf("Node has left the network\n");
// Stop ENMS service
EnmsNodeResult enmsStopStatus = ENMS_NODE_Stop(&enmsNode);
if (ENMS_NODE_RESULT_OK == enmsStopStatus) {
printf("ENMS service stopped\n");
} else {
printf("ENMS service failed to stop with status %d\n", (int)enmsStopStatus);
// Stop exemplary, user-defined custom service
// Stop MQTT-SN demo service

Handling critical errors

In cases when the embeNET stack detects a critical condition, the following handler is called by the stack, giving a chance to react:

__attribute__((noreturn)) void EXPECT_OnAbortHandler(char const* why, char const* file, int line) {
printf("Program aborted: %s %s:%i\n", why, file, line);
while(1) {

Customizing and extending the demo application

The structure of the firmware project embenet_demo_cubeide is mostly generated by STM32CubeMX application. The source *.ioc* file is included in the project. This allows you to easily customize the peripherals for your demo project as needed.

>The only requirement is NOT to change configuration of peripherals used by the port implementation, i.e. RADIO, CRYP, TIM2.

Writing or extending a custom network service.

The best starting point is to look at implementation of the existing custom_service.

Disabling "zero rule"

In order to disable the "zero rule", delete the rule with "uid": 0, from your config.json file, and add appropriate rules for your nodes, for example:

"join_rules": [
"uid": 2,
"psk": "0x1ccd738f70a35be9574738ad190f86f2"
"uid": 3,
"psk": "0xdc2eafe4016303ebb1aa1b4b2ed4fda0"

This will allow only nodes with uid = 2 and 3, to join the network, provided that their PSKs match those from config.json file.

Using custom name for network interface

You may specify the name of desired network interface in .json file, by adding on root level:

"interface_name": "your-name"

Limitations of embeNET demo application

The demo version of the embeNET stack allows to connect up to 10 nodes only, with network depth of max. 3 hops.

Go to Top