The clock driver has options that configure it's operation at build-time. A build-time option is configured by the use of a definition passed to the compiler during the build process or by adding the definition to the sys_config.h file.

CRYSTAL_MAIN_FREQ_IN
This define is the external crystal frequency used for the main oscillator.

CRYSTAL_32K_FREQ_IN
This define is rate of the RTC(32K) crystal frequency used for the chip.