Type: Number | Multiple: No

The option board_build.f_cpu is used to define MCU frequency (Hertz, Clock). A format of this option is C-like long integer value with L suffix. The 1 Hertz is equal to 1L, then 16 MHz (Mega Hertz) is equal to 16000000L.

The full list of board_build.f_cpu for the popular embedded platforms you can find in Boards section of Development Platforms. See “Frequency” column.


This option doesn’t make any changes to real clock settings on hardware. You should specify a board_build.f_cpu value if you have changed a target’s clock frequency so that the underlying software will be configured accordingly to match the change.