Hi, new member here. First post.
I have an old Diecimila and a MacBook (non-pro, 2015 model, with one USB-C port to rule them all).
When I connect the Diecimila to USB, Arduino IDE will sees it and will upload sketches fine.
But, if I disconnect and reconnect the USB cable (or otherwise remove and restore power to the Diecimila), the IDE will not find the port again. It is not listed under Tools > Port.
I get this error if I hit upload: avrdude: ser_open(): can't open device "/dev/cu.usbserial-A5002sG0"
After I reboot the computer, it works again. This is a very inconvenient workaround.
If I’m missing any crucial info, let me know.