macOS bug affecting the A-Star 32U4 Bootloader

There is a bug in macOS 10.15.1 that prevents it from using the A-Star 32U4 Bootloader. Unfortunately, this means that you will be unable to program an A-Star 32U4, Zumo 32U4, Balboa 32U4, or Romi 32U4 from a computer running macOS 10.15.1. The bug is probably present in macOS 10.15.0 too. macOS 10.15 is also known as macOS Catalina, and was released in October 2019.

If you see a large number of error messages like the ones below, then the bug is probably happening:

avrdude: ser_recv(): read error: Device not configured
avrdude: butterfly_recv(): programmer is not responding
avrdude: ser_drain(): read error: Device not configured
avrdude: ser_send(): write error: Device not configured
avrdude: ser_recv(): read error: Device not configured
avrdude: butterfly_recv(): programmer is not responding
avrdude: ser_send(): write error: Device not configured

This bug is fixed in macOS 10.15.2, so we recommend upgrading to the latest version of macOS if you encounter this bug.