Installing the OTAFIX Bootloader for nRF52 Devices

Background

When I was first getting into MeshCore I realised that nRF52 devices had the ability to do OTA updates via BLE, which is obviously a great feature when you need to update a repeater which is on a roof.

Unfortunately I never had much luck getting this to work. If you were lucky and used the right settings it might work with RAK4631, but particularly with ProMicro devices it never worked at all. This led me to dig around on GitHub where I found some ancient forgotten PRs to fix some of these issues.

Since they weren't getting any attention on the official Adafruit GitHub, I took it upon myself to fork the bootloader and include these fixes myself.

Installing the OTAFIX Bootloader for nRF52 Devices

For the best nRF52 OTA update experience, it's recommended to upgrade your device to the OTAFIX bootloader. This version includes:

Automatic fallback to OTA DFU mode if an update fails
Significantly faster OTA update speeds
Additional quality-of-life improvements for certain devices, such as the ability to enter OTA DFU mode by holding a button while resetting

1. Enter UF2 DFU Mode

First, put your device into UF2 DFU mode.

For most nRF52 devices:

Plug the device into your computer
Quickly double-press the reset button (twice within 0.5 seconds)
A UF2 USB drive should appear — the name of the drive will differ depending on the device

Some devices use different methods; see the notes at the end of this guide.

2. Check Your Current Bootloader (Optional but Recommended)

This step is important for devices like the Seeed Studio XIAO nRF52840, which often ship with the SENSE bootloader variant.

To check:

Enter UF2 DFU mode
Open the INFO_UF2.TXT file on the mounted drive

This file contains details about your current bootloader. Example: If the file shows Board-ID: nRF52840-SeeedXiaoSense-v1, you will need to install the SENSE variant.

3. Download the OTAFIX Bootloader

You can now download the OTAFIX bootloader directly from the MeshCore flasher site! Go to https://flasher.meshcore.io:

Select your device
Choose Repeater
A download link for the OTAFIX bootloader will appear in a highlighted banner — the file will be titled update-xxxx.uf2

Alternatively, the OTAFIX bootloader is also available from the official site:

https://github.com/oltaco/Adafruit_nRF52_Bootloader_OTAFIX/releases

Download the correct UF2 file for your device from the Assets section.

Files are named like: update-xxxx.uf2
You may need to click "Show more" to see all available files

Example: For the Seeed Xiao Sense variant as discussed above, you will want to download update-xiao_nrf52840_ble_sense_bootloader-0.9.2-OTAFIX2.1-BP1.2_nosd.uf2

4. Install the Bootloader

Drag and drop the update-xxxx.uf2 file onto the UF2 drive
The device will automatically:

- Update the bootloader - Reboot when complete

5. Verify the Update

Re-enter UF2 DFU mode
Open INFO_UF2.TXT again

The version line should now include OTAFIX.

Device-Specific Notes

T1000-e: Entering DFU Mode

To enter DFU mode:

Attach the magnetic USB cable
Hold the button
Quickly disconnect and reconnect the cable twice

Video reference: https://www.youtube.com/shorts/D6uo93-RcaY

ThinkNode M3: Entering DFU Mode

To enter DFU mode:

Attach the magnetic USB cable
Hold the button for approximately 25–30 seconds