For tinkering with an ATmega32U4 board, (again) I need to get the ATMEL ICE under macOS. Since High Sierra kernel extensions have to be signed and the presented workarounds of earlier posts wouldn’t work anymore. However, there is a signed kext available at the AVRFreaks forums. In my case, I downloaded the file, extracted and moved it. Additionally, I adjusted the owner and access rights. Since these files are system relevant files, you will need to do these operations as super-user.
sudo mv AtmelICE.kext /Library/Extensions/ sudo chown -R root:wheel /Library/Extensions/AtmelICE.kext sudo chmod -R 755 /Library/Extensions/AtmelICE.kext sudo kextload /Library/Extensions/AtmelICE.kext
Disconnect and reconnect your device, and it should be ready to use. For simple testing the device communication I used avrdude to talk to the device. Choose the correct programmer interface is essential for this part. If your board is using the ISP-interface, you would have to use atmelice_isp. For using JTAG, you have to use atmelice. Please check the avrdude docs for further information. You could install avrdude using homebrew.
avrdude -c atmelice_isp -p m32u4 -P usb