How to Flash Zephyr RTOS on Windows: XIAO Boards Guide

There is a growing interest in Zephyr RTOS within the embedded community. Unlike Arduino or ESP-IDF, Zephyr gives you a real hardware abstraction layer that lets you write firmware once and compile it for completely different microcontrollers without changing a single line of application code. Think of it as bringing Linux-style portability to the embedded world.

That’s exactly what I wanted to put to the test. I have four Seeed Studio XIAO modules on my bench: the nRF52840, nRF54L15, ESP32-S3, and ESP32-C6 and while they all share the same tiny 21×17.8 mm footprint and pinout, their cores are completely different. My goal is to benchmark their real-world power consumption and execution times using a single Zephyr firmware that compiles for all of them, which is precisely the kind of thing Zephyr was built for.

Before any of that, though, getting started with Zephyr can be quite complex on Windows. The official docs actually recommend against using WSL due to flashing issues. I tried that path too, and I get it: the nRF Connect extension and native Windows toolchain gave me nothing but dependency headaches. After a lot of trial and error,I concluded that WSL + usbipd-win setup that just works, across all four boards, without scripts or workarounds.

This is Part 1 of the series. Here I’ll cover:

A quick comparison of the four XIAO modules and why they make a perfect benchmark set
How to install Zephyr on Windows via WSL the right way
How to flash each board from WSL

Part 2 will get into the actual benchmarking: boot time, deep sleep current, BLE advertising duty cycle, etc.

XIAO Modules

These types of boards are basically different microcontrollers, either from Espressif or Nordic Semiconductors (ESP or nRF series), all sharing the same form factor. They offer several available pins and come with an integrated battery charger that can be powered via USB-C.

It is truly amazing to me how they can include a microcontroller (of standard size) in such a small form factor and also integrate the charging chip to connect a battery directly. Saving ourselves all the trouble of designing the charging circuitry is a total game-changer if we want to develop something while worrying as little as possible.

Furthermore, all of them besides sharing the same 21×17.8mm footprint and share the same pinout. This means that when we design a PCB, we can simply swap the board we assemble without affecting the rest of the design, allowing us to choose between several microcontrollers. This is very interesting because if, for example, Espressif or Nordic decides to release a more powerful microcontroller in the future, we could keep our original design.

NRF52840 – Click to buy

NRF54L15 – Click to buy

ESP32S3 – Click to buy

ESP32C6 – Click to buy

Specification	XIAO nRF52840	XIAO nRF54L15	XIAO ESP32-S3	XIAO ESP32-C6
CPU Architecture	ARM Cortex-M4F	ARM Cortex-M33 + RISC-V	Xtensa LX7 (dual-core)	RISC-V HP + RISC-V LP
Cores	1	2 (M33 + RISC-V)	2	2 (HP + LP)
Max Clock	64 MHz	128 MHz / 128 MHz	240 MHz (both cores)	160 MHz / 20 MHz
Flash	1 MB + 2 MB QSPI	1.5 MB NVM	8 MB	4 MB
RAM	256 KB	256 KB	8 MB PSRAM	512 KB SRAM
Wi-Fi	–	–	2.4 GHz (b/g/n)	Wi-Fi 6 (ax)
BLE	BLE 5.0	BLE 6.0	BLE 5.0	BLE 5.3
Thread / Zigbee	–	Included	–	(802.15.4)
Matter native	–	Included	–	Included
NFC	Included	–	–	–
Deep sleep	~5 µA	~0.6 µA (Sys OFF)	~9–14 µA	~15–20 µA
Onboard sensors	IMU + PDM (Sense)	IMU + PDM (Sense)	Camera + mic (Sense)	–
Zephyr name	xiao_ble	xiao_nrf54l15	xiao_esp32s3	xiao_esp32c6
Price (approx.)	~$9.90	~$9.90	~$7.99	~$6.99

Installing Zephyr on Windows via WSL

For Zephyr installation, I recommend following the project’s official getting started guide:

https://docs.zephyrproject.org/latest/develop/getting_started/index.html

Personally, I’ve noticed that if you follow the Windows steps, the documentation advises against using WSL due to various reported bugs when flashing boards. However, based on my own experience and feedback from other users, using WSL is actually the best way to integrate it with VS Code, making everything much easier to manage.

I’ve tried other recommended extensions like nRF Connect for VS Code, but I ran into a lot of dependencies issues. I personally recommend using WSL, and I will explain how to handle the flashing process. With the boards I’ve used so far, I haven’t encountered a single issue; in fact, several Reddit threads suggest that this is the preferred setup for many developers. Even if you were to run into trouble with a specific board, you could always create a simple script to move the binary out of WSL and flash it using an external tool.

Install VSCode and WSL

The first step is to install VS Code and WSL.

https://code.visualstudio.com/

Once inside VS Code, go to the extensions section and install the WSL extension.

To access it later, you can easily connect to WSL via the icon in the bottom-left corner of the interface. This will allow you to use the integrated terminal exactly as if you were running Ubuntu.

Zephyr install on WSL

Once you have WSL installed, proceed with the Zephyr installation guide by following the Ubuntu steps. I prefer not to list every single command here, as that would just be repeating what’s already in the official documentation, and the Zephyr guide is far more likely to stay updated over time than my blog!

However, I did find one crucial detail: before creating the Python virtual environment, you need to perform the following installation to ensure everything runs:

sudo apt update && sudo apt install python3.12-venv

Once you finish the installation, you should be able to compile examples using `west` by running a command like this:

cd ~/zephyrproject/zephyr west build -p always -b xiao_ble samples/basic/blinky

USBIPD install

The issue we face now is that the devices connected to your computer and listed in Windows are not automatically linked to WSL. Therefore, if you try to run:

west flash

The system won’t detect your board even if it’s physically plugged in. To fix this, we need to install usbipd-win on Windows. Download the .msi file from the official repository, making sure to select the latest release that matches your computer’s architecture:

https://github.com/dorssel/usbipd-win/releases

Once the installation is complete, you must launch PowerShell as an Administrator. This “Administrator” step is crucial; otherwise, you will run into permission issues when trying to bind the USB devices.

This tool essentially creates a bridge, allowing the Linux kernel inside WSL to “see” and interact with the physical USB hardware managed by Windows. It’s the secret sauce that makes the WSL development workflow viable for hardware hacking.

Once installed, you can run the following commands from PowerShell.

usbipd list

To make it easier, here is a quick reference table of the workflow:

Step	Command	When to use
List devices	`usbipd list`	Always first
Bind device	`usbipd bind --busid <BUSID>`	Only the first time
Connect to WSL	`usbipd attach --wsl --busid <BUSID>`	Every session
Auto-attach	`usbipd attach --wsl --busid <BUSID> --auto-attach`	Optional, very convenient
Release to Windows	`usbipd detach --busid <BUSID>`	When finished

In this case the device that we would like to connect with WSL is COM23, which is BUSID 4-1.

usbipd bind --busid 4-1 usbipd attach --wsl --busid 4-1 --auto-attach

Wait until it says “is now attached”; it might take a few seconds to complete the handshake. By using the --auto-attach flag, the system will automatically handle the reconnection if the board resets or you unplug it. This way, you can focus on your code and forget about the PowerShell window—just keep it open in the background.

Verify device detection in WSL

Once the device is attached via usbipd, it’s worth double-checking that WSL has actually picked it up before attempting to flash. Run the following commands:


# Check that the device has been recognized
lsusb# Find the assigned serial port
ls /dev/ttyACM*
ls /dev/ttyUSB*# If flashing fails due to permission errors, a quick fix:
sudo chmod 666 /dev/ttyACM0# Permanent fix (requires closing and reopening the session):
sudo usermod -a -G dialout $USER

If lsusb shows your board and a port appears under /dev/ttyACM* or /dev/ttyUSB*, you’re good to go. If nothing shows up, go back to the usbipd step and make sure the device is properly attached — it’s almost always a bind or attach issue, not a Zephyr problem.

Creating your first Zephyr application

Copy a minimal sample as your working base:

cd ~/zephyrproject cp -r zephyr/samples/basic/minimal testBenchApp

Personally, I prefer this method of creating an application rather than using the standard west init tool, but that’s just my personal opinion, feel free to use whichever workflow you prefer. By making a copy of the sample code and placing it at the same level as the zephyrproject directory, everything stays organized and your CMakeLists.txt will be ready to go without extra headaches.

Compiling with a custom build directory

Adding the -d build option allows you to compile for multiple boards in parallel without them interfering with each other, as each one will have its own custom build directory. This is especially useful if you are testing the same code on different hardware simultaneously.


# nRF54L15
west build -p always -b xiao_nrf54l15/nrf54l15/cpuapp -s testBenchApp -d build_xiao_nrf54l15# ESP32-S3
west build -b esp32s3_devkitm -s testBenchApp -d build_esp

By specifying -d build/wio_tracker, you ensure that the artifacts for the Wio Tracker don’t overwrite those of another board, keeping your workspace clean and organized.

Building and flashing each XIAO board

nRF52840 (XIAO BLE)


# Compilar blinky
west build -p always -b xiao_ble samples/basic/blinky# Compilar hello_world (variante sense)
west build -p always -b xiao_ble/nrf52840/sense samples/hello_world

The nRF52840 doesn’t flash over a standard serial port; instead, it enters a bootloader mode where it mounts itself as a USB mass storage device.

Enter Bootloader: Double-click the Reset button. The board will appear on your computer as a new USB drive.
Flash Command: Run west flash -r uf2. This command is designed to automatically find the mounted drive and copy the .uf2 file.

Note for WSL Users: Sometimes west flash -r uf2 may fail to “see” the mounted drive through the WSL layer, even with usbipd. If you run into this, don’t worry, there is a simple workaround:

Locate the compiled file in your project directory at build/zephyr/zephyr.uf2.
Open your Windows File Explorer.
Manually drag and drop that .uf2 file into the USB drive mounted by the board.

The device will automatically reboot and start running your new firmware as soon as the copy is finished.

nRF54L15 (XIAO nRF54L15)

The XIAO nRF54L15 features an onboard SAMD11 chip with integrated CMSIS-DAP, which is a total game-changer. This setup allows you to flash and debug your code directly via USB without needing any external hardware or expensive J-Link adapters. It’s essentially “plug and play” debugging right out of the box.


west build -p always -b xiao_nrf54l15/nrf54l15/cpuapp samples/hello_world
west flash

ESP32-C6 (XIAO ESP32-C6)

Before you can start building for certain architectures, you need to download the required binary blobs (like HALs and low-level drivers) that aren’t included in the main Zephyr repository for licensing reasons. Run the following command:


west blobs fetch hal_espressif

Then you can build and flash for both cpus


# High-performance core
west build -p always -b xiao_esp32c6/esp32c6/hpcore samples/hello_world# Low-power core
west build -p always -b xiao_esp32c6/esp32c6/lpcore samples/hello_worldwest flash

ESP32-S3 (XIAO ESP32-S3)


west blobs fetch hal_espressif

Then you can build and flash for both cpus


# Processing CPU (principal)
west build -p always -b xiao_esp32s3/esp32s3/procpu samples/hello_world# App CPU (secundario)
west build -p always -b xiao_esp32s3/esp32s3/appcpu samples/hello_worldwest flash

Conclusion and what's next

With this setup, you now have Zephyr fully installed and a sample project ready to compile and flash for each of your boards—simply by switching the board target in your build and flash commands.

In the next post, I will focus on adapting the firmware to perform precise measurements, covering both power consumption and execution time for common functionalities. We’ll dive into a more technical analysis of each module, providing you with the data you need to choose the best hardware for your project and truly showcasing the potential of the Zephyr RTOS.

XIAO Modules

Installing Zephyr on Windows via WSL

Install VSCode and WSL

Zephyr install on WSL

USBIPD install

Verify device detection in WSL

Creating your first Zephyr application

Compiling with a custom build directory

Building and flashing each XIAO board

nRF52840 (XIAO BLE)

nRF54L15 (XIAO nRF54L15)

ESP32-C6 (XIAO ESP32-C6)

ESP32-S3 (XIAO ESP32-S3)

Conclusion and what's next

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