bpospick:
I'm looking to power a Duemilanove (FT2332R + ATmega328P) at 3.3V. The 328P spec says that the frequency limit for 3.3V is 12MHz.Does the frequency defined in the boards.txt configuration file (atmega328.build.f_cpu=12000000L) correctly change the delay() function? I.e., will delay(1000) result in a 1 second delay? or will it become 1.33 seconds?
P.s. the flipside is to keep the board at 5V and boost the system with a20MHz crystal.
Keep in mind that many people and even a few commercial offerings (Seeeduino's 328p based board with switchable 5V or 3.3V operation comes to mind) operate their 328p chips at 16mhz at 3.3vdc and report no problems. While it is certainly outside the AVR recommended specs, you might find that it works fine for you. Not a personal recommendation, just an observation.
Lefty