watchX uses Atmega32U4 as a MCU. Atmega32U4 has an internal USB hardware. This hardware feeds from internal timer, timer 4. When your sketch messes with the timers Atmega32U4 fails to manage USB hardware so it become unresponsive. This leads not to be able to flash a sketch. In order to overwrite this situation please follow:
- Plug in the micro-USB to the watchX and your computer. Make sure the Arduino Leonardo is selected in Arduino application
- Press and hold the Reset button on the watchX. Don’t release it yet. Then hit the Upload button in the app
- Only release the Reset button after you see the message “Uploading…” appearing in the bottom left corner of the app
- Wait until it says “Done uploading” and then unplug the cable
Enjoy!