Factory Reset
The Adafruit Metro M4 Express board ships running a NeoPixel rainbow swirl example that also scans the I2C bus for sensors. It's lovely, but you probably had other plans for the board. As you start working with your board, you may want to return to the original code to begin again, or you may find your board gets into a bad state. Either way, this page has you covered.
Step 1. Download the factory-reset.uf2 file
Save the following file wherever is convenient for you. You will need to access it to copy it to your board.
Step 2. Enter M4 bootloader mode
Entering the bootloader is easy. Complete the following steps.
Before you start, make sure your microcontroller is plugged into USB port to your computer using a known good data+power USB cable. Charge-only cables will not work!
Turn on the On/Off switch - check that you see the OK light on so you know the board is powered, a prerequisite!
To enter the bootloader:
- Press and release the Reset button, twice in rapid succession. You are doing a double-click, delaying at most half a second between presses.
- The NeoPixel should go Green to show it's in UF2 bootloader mode.
- You should now see the METROM4BOOT drive appear.
The NeoPixel LED on the Metro M4 will light up in a rainbow swirl, and the Serial Port will start outputting logging information (like any I2C component addresses seen).
You've successfully returned your board to a factory reset state!
Flash Resetting UF2
If your board ever gets into a really weird state and doesn't even show up when loading code, try loading this 'nuke' UF2 which will do a 'deep clean' on your Flash Memory. You will lose all the files on the board, but at least you'll be able to revive it! Download the file below, and follow the instructions in Step 2 and Step 3 above to load this UF2. Then, start again at Step 1 to return your board to factory reset state.
UF2 firmware/app image still not working?
If your board won't accept a firmware UF2 file then there's a small chance it's using an older bootloader version.
You can check by looking at the INFO_UF2.TXT file on the M4 boot drive when available, and it will state the bootloader version (v4.0.0 on 9/9/26).
Download the file below, and follow the instructions in Step 2 and Step 3 above to load this UF2. Then, start again at Step 1 to return your board to factory reset state.
Now depending on if you're lucky enough to have one of the revision A boards (shipped before March 2018), or the revision B boards (most), you'll need to pick between the two bootloader options:
You probably want this one:
And just in case this guide hasn't been updated when you come back in a few years, you can find the latest bootloader versions here:
Page last edited September 10, 2026
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