The MCUXpresso SDK provides a driver for the Frequency Measurement (FREQME).

Function groups

The freqme module can be used to measure the frequency of the selected target clock or the pulse width of the selected reference clock. Based on features of freqme moudle, the driver can be divided into 5 function groups.

Basic Control APIs

Functions in this groups are for module basic control. The function FREQME_StartMeasurementCycle() starts the measurement cycle and function FREQME_TerminateMeasurementCycle() terminates the measurement cycle. The funciton FREQME_Init() initializes the module, before invoking that function some steps also need to do:

Reset the Frquency Measurement function peripheral reset.
Select reference and target clocks using input mux block, please note to feed selected clocks source to FREQME module.
If designed to measure external input clocks, please remember to set pin mux.

Frequency Measurement Mode Control APIs

The funciton FREQME_CalculateTargetClkFreq() calculates the frequency of selected target clock. The formula is Ftarget = (RESULT - 2) * Freference / 2 ^ REF_SCALE. And the result value in unit of Hz. To measure the frequency with a high degree of accuracy, the frequency of target clock is better less than reference clock.

Pulse Width Measurement Mode Control APIs

Functions in this groups are useful when the operate mode is set as pulse width measure mode. To measure the pulse period with a high degree of accuracy, the frequency of reference clock is better less than target clock.

Status Control APIs

Functions in this group can be used to get/clear interrupt status flags.

Interrupt Control APIs

Functions in this function group can be used to enable/disable interrupts. The module supports 3 types of interrupts: Underflow interrupt(Interrupt is active when the result is less than minumum value), Overflow interrupt(Interrupt is active when the result is greater than maximum value), Result ready interrupt(Interrupt is active when a Measurement completes and the result is ready).