use fugit::HertzU32;
use strum::FromRepr;

use crate::{
    clock::{clocks_ll::regi2c_write_mask, Clock, XtalClock},
    peripherals::{LPWR, LP_AON, PCR, PMU, TIMG0},
    rtc_cntl::RtcClock,
};

const I2C_PMU: u8 = 0x6d;
const I2C_PMU_HOSTID: u8 = 0;

const I2C_PMU_EN_I2C_RTC_DREG: u8 = 8;
const I2C_PMU_EN_I2C_RTC_DREG_MSB: u8 = 0;
const I2C_PMU_EN_I2C_RTC_DREG_LSB: u8 = 0;

const I2C_PMU_EN_I2C_DIG_DREG: u8 = 8;
const I2C_PMU_EN_I2C_DIG_DREG_MSB: u8 = 1;
const I2C_PMU_EN_I2C_DIG_DREG_LSB: u8 = 1;

const I2C_PMU_EN_I2C_RTC_DREG_SLP: u8 = 8;
const I2C_PMU_EN_I2C_RTC_DREG_SLP_MSB: u8 = 2;
const I2C_PMU_EN_I2C_RTC_DREG_SLP_LSB: u8 = 2;

const I2C_PMU_EN_I2C_DIG_DREG_SLP: u8 = 8;
const I2C_PMU_EN_I2C_DIG_DREG_SLP_MSB: u8 = 3;
const I2C_PMU_EN_I2C_DIG_DREG_SLP_LSB: u8 = 3;

const I2C_PMU_OR_XPD_RTC_REG: u8 = 8;
const I2C_PMU_OR_XPD_RTC_REG_MSB: u8 = 4;
const I2C_PMU_OR_XPD_RTC_REG_LSB: u8 = 4;

const I2C_PMU_OR_XPD_DIG_REG: u8 = 8;
const I2C_PMU_OR_XPD_DIG_REG_MSB: u8 = 5;
const I2C_PMU_OR_XPD_DIG_REG_LSB: u8 = 5;

const I2C_PMU_OR_XPD_TRX: u8 = 15;
const I2C_PMU_OR_XPD_TRX_MSB: u8 = 2;
const I2C_PMU_OR_XPD_TRX_LSB: u8 = 2;

pub(crate) fn init() {
    // * No peripheral reg i2c power up required on the target */
    unsafe {
        regi2c_write_mask(
            I2C_PMU,
            I2C_PMU_HOSTID,
            I2C_PMU_EN_I2C_RTC_DREG,
            I2C_PMU_EN_I2C_RTC_DREG_MSB,
            I2C_PMU_EN_I2C_RTC_DREG_LSB,
            0,
        );
        regi2c_write_mask(
            I2C_PMU,
            I2C_PMU_HOSTID,
            I2C_PMU_EN_I2C_DIG_DREG,
            I2C_PMU_EN_I2C_DIG_DREG_MSB,
            I2C_PMU_EN_I2C_DIG_DREG_LSB,
            0,
        );
        regi2c_write_mask(
            I2C_PMU,
            I2C_PMU_HOSTID,
            I2C_PMU_EN_I2C_RTC_DREG_SLP,
            I2C_PMU_EN_I2C_RTC_DREG_SLP_MSB,
            I2C_PMU_EN_I2C_RTC_DREG_SLP_LSB,
            0,
        );
        regi2c_write_mask(
            I2C_PMU,
            I2C_PMU_HOSTID,
            I2C_PMU_EN_I2C_DIG_DREG_SLP,
            I2C_PMU_EN_I2C_DIG_DREG_SLP_MSB,
            I2C_PMU_EN_I2C_DIG_DREG_SLP_LSB,
            0,
        );
        regi2c_write_mask(
            I2C_PMU,
            I2C_PMU_HOSTID,
            I2C_PMU_OR_XPD_RTC_REG,
            I2C_PMU_OR_XPD_RTC_REG_MSB,
            I2C_PMU_OR_XPD_RTC_REG_LSB,
            0,
        );
        regi2c_write_mask(
            I2C_PMU,
            I2C_PMU_HOSTID,
            I2C_PMU_OR_XPD_DIG_REG,
            I2C_PMU_OR_XPD_DIG_REG_MSB,
            I2C_PMU_OR_XPD_DIG_REG_LSB,
            0,
        );
        regi2c_write_mask(
            I2C_PMU,
            I2C_PMU_HOSTID,
            I2C_PMU_OR_XPD_TRX,
            I2C_PMU_OR_XPD_TRX_MSB,
            I2C_PMU_OR_XPD_TRX_LSB,
            0,
        );

        let pmu = &*crate::peripherals::PMU::PTR;

        pmu.power_pd_top_cntl().write(|w| w.bits(0));
        pmu.power_pd_hpaon_cntl().write(|w| w.bits(0));
        pmu.power_pd_hpcpu_cntl().write(|w| w.bits(0));
        pmu.power_pd_hpperi_reserve().write(|w| w.bits(0));
        pmu.power_pd_hpwifi_cntl().write(|w| w.bits(0));
        pmu.power_pd_lpperi_cntl().write(|w| w.bits(0));

        pmu.hp_active_hp_regulator0()
            .modify(|_, w| w.hp_active_hp_regulator_dbias().bits(25));
        pmu.hp_sleep_lp_regulator0()
            .modify(|_, w| w.hp_sleep_lp_regulator_dbias().bits(26));

        pmu.slp_wakeup_cntl5()
            .modify(|_, w| w.lp_ana_wait_target().bits(15));
        pmu.slp_wakeup_cntl7()
            .modify(|_, w| w.ana_wait_target().bits(1700));
    }
}

pub(crate) fn configure_clock() {
    assert!(matches!(RtcClock::xtal_freq(), XtalClock::RtcXtalFreq32M));

    RtcClock::set_fast_freq(RtcFastClock::RtcFastClockRcFast);

    let cal_val = loop {
        RtcClock::set_slow_freq(RtcSlowClock::RtcSlowClockRcSlow);

        let res = RtcClock::calibrate(RtcCalSel::RtcCalRtcMux, 1024);
        if res != 0 {
            break res;
        }
    };

    unsafe {
        let lp_aon = &*LP_AON::ptr();
        lp_aon.store1().modify(|_, w| w.bits(cal_val));
    }
}

// Terminology:
//
// CPU Reset:    Reset CPU core only, once reset done, CPU will execute from
//               reset vector
// Core Reset:   Reset the whole digital system except RTC sub-system
// System Reset: Reset the whole digital system, including RTC sub-system
// Chip Reset:   Reset the whole chip, including the analog part

/// SOC Reset Reason.
#[derive(Debug, Clone, Copy, PartialEq, Eq, FromRepr)]
pub enum SocResetReason {
    /// Power on reset
    ///
    /// In ESP-IDF this value (0x01) can *also* be `ChipBrownOut` or
    /// `ChipSuperWdt`, however that is not really compatible with Rust-style
    /// enums.
    ChipPowerOn   = 0x01,
    /// Software resets the digital core by RTC_CNTL_SW_SYS_RST
    CoreSw        = 0x03,
    /// Deep sleep reset the digital core
    CoreDeepSleep = 0x05,
    /// Main watch dog 0 resets digital core
    CoreMwdt0     = 0x07,
    /// Main watch dog 1 resets digital core
    CoreMwdt1     = 0x08,
    /// RTC watch dog resets digital core
    CoreRtcWdt    = 0x09,
    /// Main watch dog 0 resets CPU 0
    Cpu0Mwdt0     = 0x0B,
    /// Software resets CPU 0 by RTC_CNTL_SW_PROCPU_RST
    Cpu0Sw        = 0x0C,
    /// RTC watch dog resets CPU 0
    Cpu0RtcWdt    = 0x0D,
    /// VDD voltage is not stable and resets the digital core
    SysBrownOut   = 0x0F,
    /// RTC watch dog resets digital core and rtc module
    SysRtcWdt     = 0x10,
    /// Main watch dog 1 resets CPU 0
    Cpu0Mwdt1     = 0x11,
    /// Super watch dog resets the digital core and rtc module
    SysSuperWdt   = 0x12,
    /// Glitch on clock resets the digital core and rtc module
    SysClkGlitch  = 0x13,
    /// eFuse CRC error resets the digital core
    CoreEfuseCrc  = 0x14,
    /// USB UART resets the digital core
    CoreUsbUart   = 0x15,
    /// USB JTAG resets the digital core
    CoreUsbJtag   = 0x16,
    /// Glitch on power resets the digital core
    CorePwrGlitch = 0x17,
}

/// RTC SLOW_CLK frequency values
#[derive(Debug, Clone, Copy)]
pub(crate) enum RtcFastClock {
    /// Select RC_FAST_CLK as RTC_FAST_CLK source
    RtcFastClockRcFast = 0,
    #[allow(dead_code)]
    /// Select XTAL_D2_CLK as RTC_FAST_CLK source
    RtcFastClockXtalD2 = 1,
}

impl Clock for RtcFastClock {
    fn frequency(&self) -> HertzU32 {
        match self {
            RtcFastClock::RtcFastClockXtalD2 => HertzU32::Hz(16_000_000),
            RtcFastClock::RtcFastClockRcFast => HertzU32::Hz(8_000_000),
        }
    }
}

/// RTC SLOW_CLK frequency values
#[allow(clippy::enum_variant_names)]
#[derive(Debug, Clone, Copy)]
#[non_exhaustive]
pub enum RtcSlowClock {
    /// Select RC_SLOW_CLK as RTC_SLOW_CLK source
    RtcSlowClockRcSlow  = 0,
    /// Select XTAL32K_CLK as RTC_SLOW_CLK source
    RtcSlowClock32kXtal = 1,
    /// Select RC32K_CLK as RTC_SLOW_CLK source
    RtcSlowClock32kRc   = 2,
    /// Select OSC_SLOW_CLK (external slow clock) as RTC_SLOW_CLK source
    RtcSlowOscSlow      = 3,
}

impl Clock for RtcSlowClock {
    fn frequency(&self) -> HertzU32 {
        match self {
            RtcSlowClock::RtcSlowClockRcSlow => HertzU32::Hz(150_000),
            RtcSlowClock::RtcSlowClock32kXtal => HertzU32::Hz(32_768),
            RtcSlowClock::RtcSlowClock32kRc => HertzU32::Hz(32_768),
            RtcSlowClock::RtcSlowOscSlow => HertzU32::Hz(32_768),
        }
    }
}

#[derive(Debug, Clone, Copy, PartialEq)]
/// Clock source to be calibrated using rtc_clk_cal function
pub(crate) enum RtcCalSel {
    /// Currently selected RTC SLOW_CLK
    RtcCalRtcMux     = -1,
    /// Internal 150kHz RC oscillator
    RtcCalRcSlow     = 0,
    /// External 32kHz XTAL, as one type of 32k clock
    RtcCal32kXtal    = 1,
    /// Internal 32kHz RC oscillator, as one type of 32k clock
    RtcCal32kRc      = 2,
    /// External slow clock signal input by lp_pad_gpio0, as one type of 32k
    /// clock
    RtcCal32kOscSlow = 3,
    /// Internal 20MHz RC oscillator
    RtcCalRcFast,
}

#[derive(Clone)]
pub(crate) enum RtcCaliClkSel {
    CaliClkRcSlow = 0,
    CaliClkRcFast = 1,
    CaliClk32k    = 2,
}

/// RTC Watchdog Timer driver
impl RtcClock {
    /// Get main XTAL frequency.
    /// This is the value stored in RTC register RTC_XTAL_FREQ_REG by the
    /// bootloader, as passed to rtc_clk_init function.
    pub fn xtal_freq() -> XtalClock {
        match Self::read_xtal_freq_mhz() {
            None | Some(32) => XtalClock::RtcXtalFreq32M,
            Some(other) => XtalClock::RtcXtalFreqOther(other),
        }
    }

    fn set_fast_freq(fast_freq: RtcFastClock) {
        // components/hal/esp32s2/include/hal/clk_tree_ll.h
        unsafe {
            let lp_clkrst = &*LPWR::PTR;
            lp_clkrst.lp_clk_conf().modify(|_, w| {
                w.fast_clk_sel().bits(match fast_freq {
                    RtcFastClock::RtcFastClockRcFast => 0b00,
                    RtcFastClock::RtcFastClockXtalD2 => 0b01,
                })
            });
        }

        crate::rom::ets_delay_us(3);
    }

    fn set_slow_freq(slow_freq: RtcSlowClock) {
        unsafe {
            let lp_clkrst = &*LPWR::PTR;

            lp_clkrst
                .lp_clk_conf()
                .modify(|_, w| w.slow_clk_sel().bits(slow_freq as u8));
            lp_clkrst.clk_to_hp().modify(|_, w| {
                w.icg_hp_xtal32k()
                    .bit(matches!(slow_freq, RtcSlowClock::RtcSlowClock32kXtal))
                    .icg_hp_xtal32k()
                    .bit(matches!(slow_freq, RtcSlowClock::RtcSlowClock32kXtal))
            });
        }
    }

    /// Get the RTC_SLOW_CLK source
    pub fn slow_freq() -> RtcSlowClock {
        let lp_clrst = unsafe { &*LPWR::ptr() };

        let slow_freq = lp_clrst.lp_clk_conf().read().slow_clk_sel().bits();
        match slow_freq {
            0 => RtcSlowClock::RtcSlowClockRcSlow,
            1 => RtcSlowClock::RtcSlowClock32kXtal,
            2 => RtcSlowClock::RtcSlowClock32kRc,
            3 => RtcSlowClock::RtcSlowOscSlow,
            _ => unreachable!(),
        }
    }

    fn calibrate(cal_clk: RtcCalSel, slowclk_cycles: u32) -> u32 {
        let xtal_freq = RtcClock::xtal_freq();
        let xtal_cycles = RtcClock::calibrate_internal(cal_clk, slowclk_cycles) as u64;
        let divider = xtal_freq.mhz() as u64 * slowclk_cycles as u64;
        let period_64 = ((xtal_cycles << RtcClock::CAL_FRACT) + divider / 2u64 - 1u64) / divider;

        (period_64 & u32::MAX as u64) as u32
    }

    /// Calibration of RTC_SLOW_CLK is performed using a special feature of
    /// TIMG0. This feature counts the number of XTAL clock cycles within a
    /// given number of RTC_SLOW_CLK cycles.
    fn calibrate_internal(mut cal_clk: RtcCalSel, slowclk_cycles: u32) -> u32 {
        const SOC_CLK_RC_FAST_FREQ_APPROX: u32 = 17_500_000;
        const SOC_CLK_RC_SLOW_FREQ_APPROX: u32 = 136_000;
        const SOC_CLK_XTAL32K_FREQ_APPROX: u32 = 32768;

        if cal_clk == RtcCalSel::RtcCalRtcMux {
            cal_clk = match cal_clk {
                RtcCalSel::RtcCalRtcMux => match RtcClock::slow_freq() {
                    RtcSlowClock::RtcSlowClock32kXtal => RtcCalSel::RtcCal32kXtal,
                    RtcSlowClock::RtcSlowClock32kRc => RtcCalSel::RtcCal32kRc,
                    _ => cal_clk,
                },
                RtcCalSel::RtcCal32kOscSlow => RtcCalSel::RtcCalRtcMux,
                _ => cal_clk,
            };
        }

        let lp_clkrst = unsafe { &*LPWR::ptr() };
        let pcr = unsafe { &*PCR::ptr() };
        let pmu = unsafe { &*PMU::ptr() };

        let clk_src = RtcClock::slow_freq();

        if cal_clk == RtcCalSel::RtcCalRtcMux {
            cal_clk = match clk_src {
                RtcSlowClock::RtcSlowClockRcSlow => RtcCalSel::RtcCalRcSlow,
                RtcSlowClock::RtcSlowClock32kXtal => RtcCalSel::RtcCal32kXtal,
                RtcSlowClock::RtcSlowClock32kRc => RtcCalSel::RtcCal32kRc,
                RtcSlowClock::RtcSlowOscSlow => RtcCalSel::RtcCal32kOscSlow,
            };
        }

        let cali_clk_sel;
        if cal_clk == RtcCalSel::RtcCalRtcMux {
            cal_clk = match clk_src {
                RtcSlowClock::RtcSlowClockRcSlow => RtcCalSel::RtcCalRcSlow,
                RtcSlowClock::RtcSlowClock32kXtal => RtcCalSel::RtcCal32kXtal,
                RtcSlowClock::RtcSlowClock32kRc => RtcCalSel::RtcCal32kRc,
                RtcSlowClock::RtcSlowOscSlow => RtcCalSel::RtcCalRcSlow,
            }
        }

        if cal_clk == RtcCalSel::RtcCalRcFast {
            cali_clk_sel = RtcCaliClkSel::CaliClkRcFast;
        } else if cal_clk == RtcCalSel::RtcCalRcSlow {
            cali_clk_sel = RtcCaliClkSel::CaliClkRcSlow;
        } else {
            cali_clk_sel = RtcCaliClkSel::CaliClk32k;
            match cal_clk {
                RtcCalSel::RtcCalRtcMux | RtcCalSel::RtcCalRcSlow | RtcCalSel::RtcCalRcFast => {}
                RtcCalSel::RtcCal32kRc => {
                    pcr.ctrl_32k_conf()
                        .modify(|_, w| unsafe { w.clk_32k_sel().bits(0) });
                }
                RtcCalSel::RtcCal32kXtal => {
                    pcr.ctrl_32k_conf()
                        .modify(|_, w| unsafe { w.clk_32k_sel().bits(1) });
                }
                RtcCalSel::RtcCal32kOscSlow => {
                    pcr.ctrl_32k_conf()
                        .modify(|_, w| unsafe { w.clk_32k_sel().bits(2) });
                }
            }
        }

        // Enable requested clock (150k is always on)
        // Some delay is required before the time is stable
        // Only enable if originaly was disabled
        // If clock is already on, do nothing

        let dig_32k_xtal_enabled = lp_clkrst.clk_to_hp().read().icg_hp_xtal32k().bit_is_set();

        if cal_clk == RtcCalSel::RtcCal32kXtal && !dig_32k_xtal_enabled {
            lp_clkrst
                .clk_to_hp()
                .modify(|_, w| w.icg_hp_xtal32k().set_bit());
        }

        // TODO: very hacky
        // in ESP-IDF these are not called in this function but the fields are set
        lp_clkrst
            .clk_to_hp()
            .modify(|_, w| w.icg_hp_xtal32k().set_bit());
        pmu.hp_sleep_lp_ck_power()
            .modify(|_, w| w.hp_sleep_xpd_xtal32k().set_bit());

        pmu.hp_sleep_lp_ck_power()
            .modify(|_, w| w.hp_sleep_xpd_rc32k().set_bit());

        let rc_fast_enabled = pmu
            .hp_sleep_lp_ck_power()
            .read()
            .hp_sleep_xpd_fosc_clk()
            .bit_is_set();
        let dig_rc_fast_enabled = lp_clkrst.clk_to_hp().read().icg_hp_fosc().bit_is_set();

        if cal_clk == RtcCalSel::RtcCalRcFast {
            if !rc_fast_enabled {
                pmu.hp_sleep_lp_ck_power()
                    .modify(|_, w| w.hp_sleep_xpd_fosc_clk().set_bit());
                crate::rom::ets_delay_us(50);
            }

            if !dig_rc_fast_enabled {
                lp_clkrst
                    .clk_to_hp()
                    .modify(|_, w| w.icg_hp_fosc().set_bit());
                crate::rom::ets_delay_us(5);
            }
        }

        let rc32k_enabled = pmu
            .hp_sleep_lp_ck_power()
            .read()
            .hp_sleep_xpd_rc32k()
            .bit_is_set();
        let dig_rc32k_enabled = lp_clkrst.clk_to_hp().read().icg_hp_osc32k().bit_is_set();

        if cal_clk == RtcCalSel::RtcCal32kRc {
            if !rc32k_enabled {
                pmu.hp_sleep_lp_ck_power()
                    .modify(|_, w| w.hp_sleep_xpd_rc32k().set_bit());
                crate::rom::ets_delay_us(300);
            }

            if !dig_rc32k_enabled {
                lp_clkrst
                    .clk_to_hp()
                    .modify(|_, w| w.icg_hp_osc32k().set_bit());
            }
        }

        // Check if there is already running calibration process
        // TODO: &mut TIMG0 for calibration
        let timg0 = unsafe { &*TIMG0::ptr() };

        if timg0
            .rtccalicfg()
            .read()
            .rtc_cali_start_cycling()
            .bit_is_set()
        {
            timg0
                .rtccalicfg2()
                .modify(|_, w| unsafe { w.rtc_cali_timeout_thres().bits(1) });

            // Set small timeout threshold to accelerate the generation of timeot
            // Internal circuit will be reset when timeout occurs and will not affect the
            // next calibration
            while !timg0.rtccalicfg().read().rtc_cali_rdy().bit_is_set()
                && !timg0.rtccalicfg2().read().rtc_cali_timeout().bit_is_set()
            {}
        }

        // Prepare calibration
        timg0
            .rtccalicfg()
            .modify(|_, w| unsafe { w.rtc_cali_clk_sel().bits(cali_clk_sel.clone() as u8) });
        timg0
            .rtccalicfg()
            .modify(|_, w| w.rtc_cali_start_cycling().clear_bit());
        timg0
            .rtccalicfg()
            .modify(|_, w| unsafe { w.rtc_cali_max().bits(slowclk_cycles as u16) });

        let expected_freq = match cali_clk_sel {
            RtcCaliClkSel::CaliClk32k => {
                timg0.rtccalicfg2().modify(|_, w| unsafe {
                    w.rtc_cali_timeout_thres().bits(slowclk_cycles << 12)
                });
                SOC_CLK_XTAL32K_FREQ_APPROX
            }
            RtcCaliClkSel::CaliClkRcFast => {
                timg0
                    .rtccalicfg2()
                    .modify(|_, w| unsafe { w.rtc_cali_timeout_thres().bits(0x01FFFFFF) });
                SOC_CLK_RC_FAST_FREQ_APPROX
            }
            _ => {
                timg0.rtccalicfg2().modify(|_, w| unsafe {
                    w.rtc_cali_timeout_thres().bits(slowclk_cycles << 10)
                });
                SOC_CLK_RC_SLOW_FREQ_APPROX
            }
        };

        let us_time_estimate = (HertzU32::MHz(slowclk_cycles) / expected_freq).to_Hz();

        // Start calibration
        timg0
            .rtccalicfg()
            .modify(|_, w| w.rtc_cali_start().clear_bit());
        timg0
            .rtccalicfg()
            .modify(|_, w| w.rtc_cali_start().set_bit());

        // Wait for calibration to finish up to another us_time_estimate
        crate::rom::ets_delay_us(us_time_estimate);

        let cal_val = loop {
            if timg0.rtccalicfg().read().rtc_cali_rdy().bit_is_set() {
                break timg0.rtccalicfg1().read().rtc_cali_value().bits();
            }

            if timg0.rtccalicfg2().read().rtc_cali_timeout().bit_is_set() {
                // Timed out waiting for calibration
                break 0;
            }
        };

        timg0
            .rtccalicfg()
            .modify(|_, w| w.rtc_cali_start().clear_bit());

        if cal_clk == RtcCalSel::RtcCal32kXtal && !dig_32k_xtal_enabled {
            lp_clkrst
                .clk_to_hp()
                .modify(|_, w| w.icg_hp_xtal32k().clear_bit());
        }

        if cal_clk == RtcCalSel::RtcCalRcFast {
            if rc_fast_enabled {
                pmu.hp_sleep_lp_ck_power()
                    .modify(|_, w| w.hp_sleep_xpd_fosc_clk().set_bit());
                crate::rom::ets_delay_us(50);
            }

            if dig_rc_fast_enabled {
                lp_clkrst
                    .clk_to_hp()
                    .modify(|_, w| w.icg_hp_fosc().set_bit());
                crate::rom::ets_delay_us(5);
            }
        }

        if cal_clk == RtcCalSel::RtcCal32kRc {
            if rc32k_enabled {
                pmu.hp_sleep_lp_ck_power()
                    .modify(|_, w| w.hp_sleep_xpd_rc32k().set_bit());
                crate::rom::ets_delay_us(300);
            }
            if dig_rc32k_enabled {
                lp_clkrst
                    .clk_to_hp()
                    .modify(|_, w| w.icg_hp_osc32k().set_bit());
            }
        }

        cal_val
    }

    pub(crate) fn cycles_to_1ms() -> u16 {
        let period_13q19 = RtcClock::calibrate(
            match RtcClock::slow_freq() {
                RtcSlowClock::RtcSlowClockRcSlow => RtcCalSel::RtcCalRtcMux,
                RtcSlowClock::RtcSlowClock32kXtal => RtcCalSel::RtcCal32kXtal,
                RtcSlowClock::RtcSlowClock32kRc => RtcCalSel::RtcCal32kRc,
                RtcSlowClock::RtcSlowOscSlow => RtcCalSel::RtcCal32kOscSlow,
                // RtcSlowClock::RtcCalRcFast => RtcCalSel::RtcCalRcFast,
            },
            1024,
        );

        // 100_000_000 is used to get rid of `float` calculations
        let period = (100_000_000 * period_13q19 as u64) / (1 << RtcClock::CAL_FRACT);

        (100_000_000 * 1000 / period) as u16
    }

    pub(crate) fn estimate_xtal_frequency() -> u32 {
        let timg0 = unsafe { crate::peripherals::TIMG0::steal() };
        while timg0.rtccalicfg().read().rtc_cali_rdy().bit_is_clear() {}

        timg0.rtccalicfg().modify(|_, w| unsafe {
            w.rtc_cali_clk_sel()
                .bits(0) // RTC_SLOW_CLK
                .rtc_cali_max()
                .bits(100)
                .rtc_cali_start_cycling()
                .clear_bit()
                .rtc_cali_start()
                .set_bit()
        });

        timg0
            .rtccalicfg()
            .modify(|_, w| w.rtc_cali_start().set_bit());

        while timg0.rtccalicfg().read().rtc_cali_rdy().bit_is_clear() {}

        (timg0.rtccalicfg1().read().rtc_cali_value().bits()
            * (RtcSlowClock::RtcSlowClockRcSlow.frequency().to_Hz() / 100))
            / 1_000_000
    }
}