PaulStoffregen/cores — pull request #21 by duff2013 (2014-05-29 18:34:17+00:00)
Title: Added support for 2, 4, 8, 16MHz (No USB)

4, 8 and 16 MHz use the external clock in BLPE mode and 2MHz use’s internal clock in BLPI mode. This will allows for future updates to utilize VLPR with 2, 4MHz.

I tested these with Hardware Serial and SD library and they work.