Zephyr v4.2.0 includes a Wi-Fi-enabled example for the FRDM-RW612 board: zephyr/samples/net/wifi/shell. This sample demonstrates how to use Zephyr’s shell interface to manage Wi-Fi connectivity. It allows users to scan for nearby networks, connect to a specific SSID with a password, and monitor connection status—all through shell commands. The example initializes the networking stack, configures the Wi-Fi driver, and exposes commands like Wi-Fi scan and Wi-Fi connect, making it a useful tool for testing and debugging Wi-Fi features in Zephyr-based applications.
In this guide, we'll modify the mqtt_publisher example—originally designed for Ethernet—to work with Wi-Fi instead. This sample demonstrates how to implement an MQTT client in Zephyr OS that connects to a broker and publishes messages over a network. It uses Zephyr’s networking stack, supports TCP/IP and optional TLS, and sends data to a specified topic. This makes it a practical starting point for building IoT applications that communicate with cloud services or other MQTT-enabled systems.
For this guide I’m using the following software and tools:
- Visual Studio code v1.103.2
- MCUXpresso plug-in for Visual studio code v25.8.49
- Zephyr v4.2.0
You can follow this guide to setup your Zephyr environment
Procedure:
1. Use the “Import Example from Repository” tool from the MCUXpresso plug-in to import the mqtt_publisher example. It will open the README.rst file. It has a complete description of what the example does and how to run it with Ethernet.
2. Open prj.conf to add these options at the end of the file:
CONFIG_MAIN_STACK_SIZE=5200
CONFIG_SHELL_STACK_SIZE=6144
CONFIG_NET_TX_STACK_SIZE=2048
CONFIG_NET_RX_STACK_SIZE=2048
CONFIG_NET_PKT_RX_COUNT=10
CONFIG_NET_PKT_TX_COUNT=10
CONFIG_NET_BUF_RX_COUNT=20
CONFIG_NET_BUF_TX_COUNT=20
CONFIG_NET_MAX_CONTEXTS=10
CONFIG_NET_DHCPV4=y
CONFIG_NET_IPV6=n
CONFIG_INIT_STACKS=y
CONFIG_NET_STATISTICS=y
CONFIG_NET_STATISTICS_PERIODIC_OUTPUT=n
CONFIG_WIFI=y
CONFIG_WIFI_LOG_LEVEL_ERR=y
CONFIG_NET_L2_WIFI_SHELL=y
CONFIG_NET_MGMT_EVENT_QUEUE_TIMEOUT=5000
CONFIG_NET_MGMT_EVENT_QUEUE_SIZE=16
CONFIG_WIFI_NXP=y
CONFIG_NXP_RW610=y
CONFIG_ETH_DRIVER=n
CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE=2048
CONFIG_NET_MGMT_EVENT_STACK_SIZE=4608
CONFIG_NET_TCP_WORKQ_STACK_SIZE=2048
CONFIG_IDLE_STACK_SIZE=1024
These Zephyr configurations enable Wi-Fi networking on an NXP RW610-based board (e.g., FRDM-RW612) by activating the necessary drivers and protocols, including DHCPv4 for automatic IP assignment. It allocates generous stack sizes for key system components like the shell, main thread, network management, and TCP workqueues to ensure stability and responsiveness. The configuration also sets up buffer and packet count to handle moderate network traffic, disables unused features like Ethernet and IPv6, and enables diagnostic tools such as heap initialization and network statistics. Additionally, it configures the shell and Wi-Fi layers to support runtime commands and scanning, while tuning event queue parameters to improve reliability in crowded environments.
3. Now modify the example to play well with Wi-Fi. It originally tries to connect to the broker right after boot. We will change it to make it wait for a command that we can call on the shell to start the MQTT application once the board is connected to the Wi-Fi network.
a. On src/main.c add these includes:
#include <zephyr/shell/shell.h>
#include <zephyr/kernel.h>
shell.h - This header provides access to Zephyr’s shell subsystem, which allows you to define and register custom shell commands.
kernel.h - This is the core kernel header in Zephyr. It provides access to fundamental OS features such as Semaphores.
b. Also on src/main.c, add this code before start_app()
K_SEM_DEFINE(mqtt_pub_sem, 0, 1);
static int my_cmd_handler(const struct shell *shell, size_t argc, char **argv)
{
shell_print(shell, "Starting the MQTT publisher!");
k_sem_give(&mqtt_pub_sem);
return 0;
}
SHELL_CMD_REGISTER(start_mqtt, NULL, "Starts the MQTT publisher.", my_cmd_handler);
This code defines a custom shell command in Zephyr OS that triggers an MQTT publishing process using a semaphore. It also creates a binary semaphore named mqtt_pub_sem with an initial count of 0, meaning any thread waiting on it will block until it's given.
The function my_cmd_handler() is the shell command handler that releases the semaphore, signaling that the MQTT publisher can start.
The code also registers a command named “start_mqtt” with the shell, allowing users to type “start_mqtt” in the Zephyr shell to initiate the MQTT publishing process.
c. Also on src/main.c, now modify start_app() to wait for the semaphore. Put this line of code right before the start of the while loop.
k_sem_take(&mqtt_pub_sem, K_FOREVER);
d. Update the MQTT broker address in config.h to account for your broker on the Wi-Fi Network.
#define SERVER_ADDR "192.168.1.10"
4. Enable the Standby node on the Device tree. For this create an overlay file in the folder boards/ named frdm_rw612.overlay with this content:
&standby {
status = "okay";
};
Now you can build your project and load it into a FRDM-RW612. To execute it, you will need a broker running on the same Wi-Fi Network and a terminal program to get access to the Zephyr’s shell.
Use these commands to connect your board to the Wi-Fi Network and start the MQTT publisher application:
$ wifi scan
This command initiates a scan for nearby Wi-Fi networks using the board's Wi-Fi interface. It lists available SSIDs, signal strengths, and security types, helping the user identify which networks are in range and available for connection.
$ wifi connect -s my_ssid -p my_key -k 1
This command connects the device to a Wi-Fi network.
-s my_ssid specifies the name of the Wi-Fi network (SSID).
-p my_key provides the password or pre-shared key for the network.
-k 1 indicates the key management type (e.g., WPA/WPA2).
Once executed, the device attempts to associate and authenticate with the specified network.
$ start_mqtt
This is the custom shell command (defined in your application) that signals the start of the MQTT publishing process.
