Number | Multiple:
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
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
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.