On some ItsyBitsy M4 Express boards manufactured before late 2018, the factory bootloader was not protected against accidental overwriting. Normally, the bootloader is unlikely to be damaged, but certain buggy programs and certain development environments might overwrite the bootloader. If you have one of these boards, we recommend you update the bootloader, which will protect it against overwriting as part of the updating process.
To see if your board needs updating, double-click the reset button, and look at the
INFO_UF2.TXT file in
ITSYM4BOOT. If the bootloader version listed is earlier than "
UF2 Bootloader v2.0.0-adafruit.7", you should update. Download the bootloader updater below. Double-click the reset button and wait for the
ITSYM4BOOT drive to appear. Then drag or copy the updater to
ITSYM4BOOT. Wait for
ITSYM4BOOT to reappear. Your bootloader is now protected against overwriting.
After updating, you'll need to reload CircuitPython or whatever other program was loaded on the board. Your
CIRCUITPY drive is not affected by the updater on theItsyBitsy M4 Express, because it's on a separate SPI flash chip.