What does Teensyduino set for the fuses on the Teensy 2.0? Specifically, the low fuses used to set the clock speed. The boards.txt file only sets F_CPU, so it seems that Teensyduino must be looking at the CPU speed and then setting the fuses correctly. I'm curious because looking at the ATmega32U4 fuses and datasheet, I can't figure out how the clock speed is able to be set to 2 MHz and 4 MHz. 1 MHz, 8 MHz, and 16 MHz I understand, but how is 2 MHz and 4 MHz selected when the crystal is 16 MHz?

I'm also interested in the startup time you set for power-down and reset. It seems the Teensy boots much faster than say an Uno, which must have to do with the startup time fuse settings. My guess is that the Uno goes with safe settings (16k CK/14 CK + 65ms) but the Teensy uses a much shorter startup time fuse settings.

I guess what I'd like to know is what Teensyduino sets for the fuse settings for the different menu options in the Arduino IDE. I'm trying to move a Teensy 2.0 project to a bare 328P and trying to create similar characteristics.

As always, thanks for this wonderful platform and support!