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##

# 3.42.10 Frequency Meter (FREQM)

The Frequency Meter (FREQM) can be used to accurately measure the frequency of a clock by comparing it to a known reference clock.

## Using The Library

AFEC converts all the enabled channels on software or hardware triggers. It provides both polling and callback methods to indicate the end of conversion to read the converted data from the result registers.

- With polling, the application will need to continuously poll to check if the conversion is completed.

- With callback, the registered callback function will be called once the conversion is completed. This means the application do not have to poll continuously.

Callback method

This example demonstrates frequency measurement with callback.

    void AFEC_EventHandler(uintptr_t context)
    {
        uint32_t frequencyInHertz;

        if(FREQM_ErrorGet() == FREQM_ERROR_NONE)
        {
            frequencyInHertz = FREQM_FrequencyGet();
        }
    }

    int main(void)
    {
        FREQM_CallbackRegister(&amp;FREQ_EventHandler,(uintptr_t)NULL);

        FREQM_MeasurementStart();

    }

Polling method

This example demonstrates frequency measurement with polling

    uint32_t frequencyInHertz;

    /* Start Frequency Measurement */
    FREQM_MeasurementStart();

    /* Wait for measurement completion */
    while(FREQM_IsBusy());

    /* Read the result */
    if(FREQM_ErrorGet() == FREQM_ERROR_NONE)
    {
        frequencyInHertz = FREQM_FrequencyGet();
    }

## Library Interface

Frequency Meter peripheral library provides the following interfaces:

Functions

Name | Description
--- | ---
FREQM_Initialize | Initializes FREQM module
FREQM_MeasurementStart | This function starts the frequency measurement
FREQM_CallbackRegister | Allows application to register a callback function
FREQM_IsBusy | Returns the measurement status of an on-going frequency measurement operation
FREQM_FrequencyGet | Returns the measured frequency in Hz
FREQM_ErrorGet | Returns error that may have occurred during the frequency measurement process

Data types and constants

Name | Type | Description
--- | --- | ---
FREQM_ERROR | Enum | Identifies the possible FREQM module errors
FREQM_CALLBACK | Typedef | Pointer to a FREQM CallBack function