Datasheet

select Feather 32u4 for ATMega32u4 based boards! Do not use anything else, do not use

the 32u4 breakout board line.

If you have a Feather M0 (look on the board to read what it is you have) Make sure you

select Feather M0 - do not use 32u4 or Arduino Zero

I'm having problems with COM ports and my Feather 32u4/M0

Theres two COM ports you can have with the 32u4/M0, one is the user port and one is

the bootloader port. They are not the same COM port number!

When you upload a new user program it will come up with a user com port, particularly if

you use Serial in your user program.

If you crash your user program, or have a program that halts or otherwise fails, the user

com port can disappear.

When the user COM port disappears, Arduino will not be able to automatically start the

bootloader and upload new software.

So you will need to help it by performing the click-during upload procedure to re-start the

bootloader, and upload something that is known working like "Blink"

I don't understand why the COM port disappears, this does not happen on my Arduino

UNO!

UNO-type Arduinos have a

seperate

serial port chip (aka "FTDI chip" or "Prolific PL2303"

etc etc) which handles all serial port capability seperately than the main chip. This way if

the main chip fails, you can always use the COM port.

M0 and 32u4-based Arduinos do not have a seperate chip, instead the main processor

performs this task for you. It allows for a lower cost, higher power setup...but requires a

little more effort since you will need to 'kick' into the bootloader manually once in a while

I'm trying to upload to my 32u4, getting "avrdude: butterfly_recv(): programmer is not

responding" errors

This is likely because the bootloader is not kicking in and you are accidentally trying to

upload to the wrong COM port

The best solution is what is detailed above: manually upload Blink or a similar working

sketch by hand by manually launching the bootloader