# 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
# 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