If there are problems, check
- Is the correct board selected in the Arduino software?
- Is the correct serial port selected in the Arduino software (not applicable for Micronucleus bootloader)?
- Is the board detected, check Windows Device Manager or under Linux run
dmesg | grep usb
- If the board is not detected, try to install the latest drivers:
Driver Installation Guide for Windows
- Troubleshooting Guide from Arduino
Micronucleus Driver Installation
Download and Extract/Unzip: Micronucleus Driver (ATtiny)
The Micronucleus bootloader is started, if the board is new and no user program is flashed or after the reset button is pressed.
On Nanite841 boards the on-board LED is blinking, when the bootloader is running.