pub fn rtc_calib_init_code(_unit: u8, atten: Attenuation) -> Option<u16> {
        let version = Self::rtc_calib_version();

        if version > 4 {
            return None;
        }

        // See: <https://github.com/espressif/esp-idf/blob/be06a6f/components/efuse/esp32h2/esp_efuse_table.csv#L76-L79>
        let init_code: u16 = Self::read_field_le(match atten {
            Attenuation::_0dB => ADC1_AVE_INITCODE_ATTEN0,
            Attenuation::_2p5dB => ADC1_AVE_INITCODE_ATTEN1,
            Attenuation::_6dB => ADC1_AVE_INITCODE_ATTEN2,
            Attenuation::_11dB => ADC1_AVE_INITCODE_ATTEN3,
        });

        Some(init_code + 1600) // version 1 logic
    }
Get ADC initial code for specified attenuation from efuse

See: <https://github.com/espressif/esp-idf/blob/be06a6f/components/efuse/esp32h2/esp_efuse_rtc_calib.c#L33>
esp-hal/src/soc/esp32h2/efuse/mod.rs