27.6.1 Principle of Operation

FREQM counts the number of periods of the measured clock (GCLK_FREQM_MSR) with respect to the reference clock (GCLK_FREQM_REF). The measurement is done for a period of REFNUM/f_{CLK_REF} and stored in the Value register (VALUE.VALUE). REFNUM is the number of Reference clock cycles selected in the Configuration A register (CFGA.REFNUM).

The frequency of the measured clock, $f_{CLK_MSR}$ , is calculated by

f_{CLK_MSR} = (\frac{VALUE}{REFNUM}) f_{CLK_REF}

. The error can be maximum two measured clock cycles.

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