Code

Create an rtc_module struct and add to the main application source file, outside of any functions:

struct rtc_module rtc_instance;

The following must be added to the user application:

Function for setting up the module:

void configure_rtc_count(void)
{
    struct rtc_count_config config_rtc_count;
    rtc_count_get_config_defaults(&config_rtc_count);

    config_rtc_count.prescaler           = RTC_COUNT_PRESCALER_DIV_1;
    config_rtc_count.mode                = RTC_COUNT_MODE_16BIT;
#ifdef FEATURE_RTC_CONTINUOUSLY_UPDATED
    config_rtc_count.continuously_update = true;
#endif
    rtc_count_init(&rtc_instance, RTC, &config_rtc_count);

    rtc_count_enable(&rtc_instance);
}

Callback function:

void rtc_overflow_callback(void)
{
    /* Do something on RTC overflow here */
    port_pin_toggle_output_level(LED_0_PIN);
}

Function for setting up the callback functionality of the driver:

void configure_rtc_callbacks(void)
{
    rtc_count_register_callback(
            &rtc_instance, rtc_overflow_callback, RTC_COUNT_CALLBACK_OVERFLOW);
    rtc_count_enable_callback(&rtc_instance, RTC_COUNT_CALLBACK_OVERFLOW);
}

Add to user application main():

/* Initialize system. Must configure conf_clocks.h first. */
system_init();

/* Configure and enable RTC */
configure_rtc_count();

/* Configure and enable callback */
configure_rtc_callbacks();

/* Set period */
rtc_count_set_period(&rtc_instance, 2000);