41.5.2.1 Initialization

Before enabling FREQM, the device and peripheral must be configured:

Each of the generic clocks (GCLK_FREQM_REF and GCLK_FREQM_MSR) must be configured and enabled. Find CLK_FREQM_REF and GCLK_FREQM_MSR values listed in Table 12-9. PCHCTRLm Mapping.
Important: The reference clock must be slower than the measurement clock.
Write the number of Reference clock cycles for which the measurement is to be done in the Configuration A register (CFGA.REFNUM). This must be a non-zero number.

The following register is enable-protected, that is it can only be written when the FREQM is disabled: (CTRLA.ENABLE=0):The Configuration A register (CFGA)

Enable-protection is denoted by the "Enable-Protected" property in the register description.