F_CPU is defined but looks like it is not in use

[Linar Yusupov (lyusupov)]

Does it mean that the CPU frequency is hardcoded in each 'variant' SDK library file and can not be changed to a lower MHZ value ?

[Tamas Jozsi (silabs-bozont)]

Hello Linar Yusupov (@lyusupov),
Your observation is correct - it's not used anywhere in the code. It's only defined for compatibility reasons - we might remove this in the future.
We have a separate API for changing the CPU clock speed:
setCPUClock() - sets the CPU clock speed - it can be one of CPU_39MHZ, CPU_76MHZ, CPU_80MHZ
Note, that the radio variants are calibrated to work with a 39 MHz clock.