AVR Freaks

USB enumeration (if this is the correct term for this) is a bit of a nuisanse.

It's trying to do some "smart" stuff just in case you happen to plug some similar (or identical) devices in your USB ports.

Note that you do not have serial COM ports. It's all emulated in software.

If you read the documentation of the driver of the USB <==> Serial bridge you are using you might find an option to assign a specific comport number to your arduino.

These chips usually need an external eeprom to hold the product ID and vendor ID (serial number etch) to uniquely identify to your PC what device you plugged in this time.

Me, myself, I don't bother with bootloaders and such but just use plain old regular pretty reliable USBasp on my linux box.

There is no reference to a serial port whatsoever in the make target I use to program an AVR:

program: main.hex
	avrdude -p $(MCU) -c usbasp -qe -U flash:w:main.hex:i

Ps:

Mac's are somewhat like linux.

You can use "lsusb" or: "dmesg -tail" on the commandline to give you an idea of how your PC has configured your device.