Function esp_idf_sys::ets_get_apb_freq

pub unsafe extern "C" fn ets_get_apb_freq() -> u32

@brief Get apb_freq value, If value not stored in RTC_STORE5, than store.

@param None

@return uint32_t : if rtc store the value (RTC_STORE5 high 16 bits and low 16 bits with same value), read from rtc register. clock = (REG_READ(RTC_STORE5) & 0xffff) << 12; else store ets_get_detected_xtal_freq() in.