-
-# Input clock frequency.
-# This will define a symbol, F_USB, in all source code files equal to the
-# input clock frequency (before any prescaling is performed) in Hz. This value may
-# differ from F_CPU if prescaling is used on the latter, and is required as the
-# raw input clock is fed directly to the PLL sections of the AVR for high speed
-# clock generation for the USB and other AVR subsections. Do NOT tack on a 'UL'
-# at the end, this will be done automatically to create a 32-bit value in your
-# source code.
-#
-# If no clock division is performed on the input clock inside the AVR (via the
-# CPU clock adjust registers or the clock division fuses), this will be equal to F_CPU.