17.6.2.1 Initialization

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

Each of the generic clocks (GCLK_FREQM_REF and GCLK_FREQM_MSR) should be configured and enabled. Note that the reference clock should be slower than the measurement clock.
The Number of Reference Clock Cycles value in the Configuration A register (CFGA.REFNUM) must be written to a value greater than 0x00.

The following register is enable-protected, meaning that it can only be written when the FREQM is disabled (CTRLA.ENABLE is zero):

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

For further information, refer to the GCLK.