Flashing a Dock 3 Firmware with Web Serial

This article explains how to manually flash Dock 3 with an official Unfolded Circle firmware using a Chrome, Edge, or Opera web browser. For browser support details, see the Web Serial browser compatibility table.

‼️ Manual flashing is usually not required. It is mainly needed if you previously installed a custom firmware such as ESPHome and want to restore the original Dock 3 software.

Step 1 – Connect Dock 3

1. Connect Dock 3 to your PC with a USB cable.
2. Make sure only one dock is connected so the correct serial port can be selected.

Step 2 – Download the firmware

1. Go to the Dock 3 firmware releases: https://github.com/unfoldedcircle/ucd3-firmware/releases
2. Choose the desired release, usually the latest version.

3. Under Assets, download the file named:

   UCD3-firmware_r4-v<VERSION>.tar.gz.

4. Extract the downloaded archive; it contains several .bin files needed for flashing.

Step 3 – Open the web flasher

1. Open the Espressif web-based serial flasher in a supported browser: https://espressif.github.io/esptool-js/
2. Only recent versions of Chrome, Edge, and Opera support Web Serial; other browsers are not supported.

Step 4 – Connect to Dock 3

1. Click Connect on the ESP Tool web page.
2. In the browser dialog, select the device named USB JTAG/serial debug unit and click Connect.
   
   • If you are unsure which device to pick, unplug Dock 3 and plug it in again while the dialog is open; the correct entry will disappear and reappear.

If the port cannot be opened

If you see an error such as:

Connecting... Error: Failed to execute 'setSignals' on 'SerialPort': Failed to set control signals.

• Manually reload the web page and try connecting again.

After a successful connection, the web app shows the connected device details.

Step 5 – Add firmware files and addresses

Add the following files with the corresponding flash addresses:

1. Click Choose file, select the file, and enter the flash address.
2. Click Add File to add the next entry until all files are listed as below:

• 0x0 – bootloader.bin
• 0x8000 – partition-table.bin
• 0x8d000 – ota_data_initial.bin
• 0x90000 – ucd3-firmware.bin

Step 6 – Program the device

1. Double-check that all flash addresses and filenames are correct.
2. Click Program.
3. Wait until all files are written and the log window confirms completion and verification.

Step 7 – Restart Dock 3

1. Unplug the USB cable and plug it in again; Dock 3 does not automatically restart after flashing.
2. Dock 3 now runs the newly flashed firmware.