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.
- 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,
meaning that it can only be written when the FREQM is disabled (CTRLA.ENABLE=0):
- Configuration A register (CFGA)
Enable-protection is denoted by the
"Enable-Protected" property in the register description.