//! This module allows for serial communication using the STM32 U[S]ART peripheral
//! It provides APIs to configure, read, and write from
//! U[S]ART, with blocking, nonblocking, and DMA functionality.

// todo: Synchronous mode.
// todo: Auto baud

// todo: Missing some features (like additional interrupts) on the USARTv3 peripheral . (L5, G etc)

use core::ops::Deref;

use cfg_if::cfg_if;

// #[cfg(feature = "embedded_hal")]
// use embedded_hal::{
//     blocking,
//     serial::{Read, Write},
// };
// #[cfg(feature = "embedded_hal")]
// use nb;
#[cfg(any(feature = "f3", feature = "l4"))]
use crate::dma::DmaInput;
#[cfg(not(any(feature = "f4", feature = "l552", feature = "h5")))]
use crate::dma::{self, ChannelCfg, DmaChannel};
#[cfg(feature = "g0")]
use crate::pac::DMA as DMA1;
#[cfg(not(any(feature = "g0", feature = "h5")))]
use crate::pac::DMA1;
use crate::{
    clocks::Clocks,
    pac::{self, RCC},
    util::{BaudPeriph, RccPeriph},
    MAX_ITERS,
};

// todo: Prescaler (USART_PRESC) register on v3 (L5, G, H etc)

#[derive(Clone, Copy)]
#[repr(u8)]
/// The number of stop bits. (USART_CR2, STOP)
pub enum StopBits {
    S1 = 0b00,
    S0_5 = 0b01,
    S2 = 0b10,
    S1_5 = 0b11,
}

#[derive(Clone, Copy, PartialEq)]
/// Parity control enable/disable, and even/odd selection (USART_CR1, PCE and PS)
pub enum Parity {
    EnabledEven,
    EnabledOdd,
    Disabled,
}

#[derive(Clone, Copy)]
/// The length of word to transmit and receive. (USART_CR1, M)
pub enum WordLen {
    W8,
    W9,
    W7,
}

impl WordLen {
    /// We use this function due to the M field being split into 2 separate bits.
    /// Returns M1 val, M0 val
    pub fn bits(&self) -> (u8, u8) {
        match self {
            Self::W8 => (0, 0),
            Self::W9 => (0, 1),
            Self::W7 => (1, 0),
        }
    }
}

#[derive(Clone, Copy)]
#[repr(u8)]
/// Set Oversampling16 or Oversampling8 modes.
pub enum OverSampling {
    O16 = 0,
    O8 = 1,
}

#[derive(Clone, Copy, PartialEq)]
pub enum IrdaMode {
    /// "IrDA mode disabled
    None,
    /// "IrDA SIR rx/tx enabled in 'normal' mode"
    Normal,
    /// "IrDA SIR 'low-power' mode"
    LowPower,
}

/// Serial error
#[non_exhaustive]
#[derive(Debug)]
pub enum UartError {
    /// Framing error
    Framing,
    /// Noise error
    Noise,
    /// RX buffer overrun
    Overrun,
    /// Parity check error
    Parity,
    Hardware,
}

#[cfg(not(feature = "f4"))]
#[derive(Clone, Copy)]
/// The type of USART interrupt to configure. Reference the USART_ISR register.
pub enum UsartInterrupt {
    /// If the inner value of this is `Some`, its inner value will set
    /// the character to match on `enable_interrupt`. The option's value doesn't
    /// affect anything when stopping or clearing interrupts.
    CharDetect(Option<u8>),
    Cts,
    EndOfBlock,
    Idle,
    FramingError,
    LineBreak,
    Overrun,
    ParityError,
    ReadNotEmpty,
    ReceiverTimeout,
    #[cfg(not(any(feature = "f3", feature = "l4")))] // todo: PAC ommission?
    Tcbgt,
    TransmissionComplete,
    TransmitEmpty,
}

/// Configuration for Usart. Can be used with default::Default.
pub struct UsartConfig {
    /// Word length. Defaults to 8-bits.
    pub word_len: WordLen,
    /// Stop bits: Defaults to 1.
    pub stop_bits: StopBits,
    /// Oversampling rate. Defaults to 16x.
    pub oversampling: OverSampling,
    /// Enable or disable parity control. Defaults to disabled.
    pub parity: Parity,
    /// IrDA mode: Enables this protocol, which is used to communicate with IR devices.
    pub irda_mode: IrdaMode,
    #[cfg(any(feature = "g4", feature = "h7"))]
    /// The first-in, first-out buffer is enabled. Defaults to enabled.
    pub fifo_enabled: bool,
    #[cfg(not(feature = "f4"))]
    /// Optionally, disable the overrun functionality. Defaults to `false`.
    pub overrun_disabled: bool,
}

impl Default for UsartConfig {
    fn default() -> Self {
        Self {
            word_len: WordLen::W8,
            stop_bits: StopBits::S1,
            oversampling: OverSampling::O16,
            parity: Parity::Disabled,
            irda_mode: IrdaMode::None,
            #[cfg(any(feature = "g4", feature = "h7"))]
            fifo_enabled: true,
            #[cfg(not(feature = "f4"))]
            overrun_disabled: false,
        }
    }
}

// Sep macros due to too many feature-gates.
// todo: Use functions?

// todo: Support fifo_disabled regs.

#[cfg(feature = "h5")]
macro_rules! cr1 {
    ($regs:expr) => {
        $regs.cr1_enabled()
    };
}

#[cfg(not(feature = "h5"))]
macro_rules! cr1 {
    ($regs:expr) => {
        $regs.cr1
    };
}

// Some variants like H5 and certain G0 variants use separate registers for FIFO
#[cfg(feature = "h5")]
macro_rules! isr {
    ($regs:expr) => {
        $regs.isr_enabled()
    };
}

#[cfg(not(feature = "h5"))]
macro_rules! isr {
    ($regs:expr) => {
        $regs.isr
    };
}

/// Represents the USART peripheral, for serial communications.
pub struct Usart<R> {
    pub regs: R,
    baud: u32,
    config: UsartConfig,
}

impl<R> Usart<R>
where
    R: Deref<Target = pac::usart1::RegisterBlock> + RccPeriph + BaudPeriph,
{
    /// Initialize a U[s]ART peripheral, including configuration register writes, and enabling and
    /// resetting its RCC peripheral clock. `baud` is the baud rate, in bytes-per-second.
    pub fn new(regs: R, baud: u32, config: UsartConfig, clock_cfg: &Clocks) -> Self {
        let rcc = unsafe { &(*RCC::ptr()) };
        R::en_reset(rcc);

        let mut result = Self { regs, baud, config };

        // This should already be disabled on power up, but disable here just in case;
        // some bits can't be set with USART enabled.

        result.disable();

        // Set up transmission. See L44 RM, section 38.5.2: "Character Transmission Procedures".
        // 1. Program the M bits in USART_CR1 to define the word length.

        let word_len_bits = result.config.word_len.bits();
        cr1!(result.regs).modify(|_, w| {
            w.over8().bit(result.config.oversampling as u8 != 0);
            w.pce().bit(result.config.parity != Parity::Disabled);
            cfg_if! {
                if #[cfg(not(any(feature = "f3", feature = "f4", feature = "wl")))] {
                    w.m1().bit(word_len_bits.0 != 0);
                    w.m0().bit(word_len_bits.1 != 0);
                    return w.ps().bit(result.config.parity == Parity::EnabledOdd);
                } else {
                    return w.ps().bit(result.config.parity == Parity::EnabledOdd);
                }
            }
        });

        // todo: Workaround due to a PAC bug, where M0 is missing.
        #[cfg(any(feature = "f3", feature = "f4"))]
        result.regs.cr1.write(|w| unsafe {
            w.bits(
                result.regs.cr1.read().bits()
                    | ((word_len_bits.0 as u32) << 28)
                    | ((word_len_bits.1 as u32) << 12),
            )
        });

        #[cfg(not(feature = "f4"))]
        result
            .regs
            .cr3
            .modify(|_, w| w.ovrdis().bit(result.config.overrun_disabled));

        // Must be done before enabling.
        #[cfg(any(feature = "g4", feature = "h7"))]
        result
            .regs
            .cr1
            .modify(|_, w| w.fifoen().bit(result.config.fifo_enabled));

        // 2. Select the desired baud rate using the USART_BRR register.
        result.set_baud(baud, clock_cfg).ok();
        // 3. Program the number of stop bits in USART_CR2.
        result
            .regs
            .cr2
            .modify(|_, w| unsafe { w.stop().bits(result.config.stop_bits as u8) });
        // 4. Enable the USART by writing the UE bit in USART_CR1 register to 1.
        result.enable();

        // 5. Select DMA enable (DMAT[R]] in USART_CR3 if multibuffer communication is to take
        // place. Configure the DMA register as explained in multibuffer communication.
        // (Handled in `read_dma()` and `write_dma()`)
        // 6. Set the TE bit in USART_CR1 to send an idle frame as first transmission.
        // 6. Set the RE bit USART_CR1. This enables the receiver which begins searching for a
        // start bit.

        cr1!(result.regs).modify(|_, w| {
            w.te().set_bit();
            w.re().set_bit()
        });

        match result.config.irda_mode {
            // See G4 RM, section 37.5.18: USART IrDA SIR ENDEC block
            // " IrDA mode is selected by setting the IREN bit in the USART_CR3 register. In IrDA mode,
            // the following bits must be kept cleared:
            // • LINEN, STOP and CLKEN bits in the USART_CR2 register,
            IrdaMode::None => (),
            _ => {
                result.regs.cr2.modify(|_, w| unsafe {
                    w.linen().clear_bit();
                    w.stop().bits(0);
                    w.clken().clear_bit()
                });

                // • SCEN and HDSEL bits in the USART_CR3 register."
                result.regs.cr3.modify(|_, w| {
                    w.scen().clear_bit();
                    w.hdsel().clear_bit();
                    w.irlp().bit(result.config.irda_mode == IrdaMode::LowPower);
                    w.iren().set_bit()
                });
            }
        }

        result
    }

    /// Enable this U[s]ART peripheral.
    pub fn enable(&mut self) {
        cr1!(self.regs).modify(|_, w| w.ue().set_bit());
        while cr1!(self.regs).read().ue().bit_is_clear() {}
    }

    /// Disable this U[s]ART peripheral.
    pub fn disable(&mut self) {
        cr1!(self.regs).modify(|_, w| w.ue().clear_bit());
        while cr1!(self.regs).read().ue().bit_is_set() {}
    }

    /// Set the BAUD rate. Called during init, and can be called later to change BAUD
    /// during program execution.
    pub fn set_baud(&mut self, baud: u32, clock_cfg: &Clocks) -> Result<(), UartError> {
        let originally_enabled = cr1!(self.regs).read().ue().bit_is_set();

        if originally_enabled {
            cr1!(self.regs).modify(|_, w| w.ue().clear_bit());
            let mut i = 0;
            while cr1!(self.regs).read().ue().bit_is_set() {
                i += 1;
                if i >= MAX_ITERS {
                    return Err(UartError::Hardware);
                }
            }
        }

        // To set BAUD rate, see L4 RM section 38.5.4: "USART baud rate generation".
        // todo: This assumes the USART clock is APB1 or 2 depending on which USART.
        // todo: Take into account the selectable USART clock in both
        // todo util::baud implementation, and `clocks` module.
        let fclk = R::baud(clock_cfg);

        let usart_div = match self.config.oversampling {
            OverSampling::O16 => fclk / baud,
            OverSampling::O8 => 2 * fclk / baud,
        };

        // USARTDIV is an unsigned fixed point number that is coded on the USART_BRR register.
        // • When OVER8 = 0, BRR = USARTDIV.
        // • When OVER8 = 1
        // – BRR[2:0] = USARTDIV[3:0] shifted 1 bit to the right.
        // – BRR[3] must be kept cleared.
        // – BRR[15:4] = USARTDIV[15:4]
        // todo: BRR needs to be modified per the above if on oversampling 8.

        self.regs.brr.write(|w| unsafe { w.bits(usart_div as u32) });

        self.baud = baud;

        if originally_enabled {
            cr1!(self.regs).modify(|_, w| w.ue().set_bit());
        }

        Ok(())
    }

    /// Transmit data, as a sequence of u8. See L44 RM, section 38.5.2: "Character transmission procedure"
    pub fn write(&mut self, data: &[u8]) -> Result<(), UartError> {
        // todo: how does this work with a 9 bit words? Presumably you'd need to make `data`
        // todo take `&u16`.

        // 7. Write the data to send in the USART_TDR register (this clears the TXE bit). Repeat this
        // for each data to be transmitted in case of single buffer.

        cfg_if! {
            if #[cfg(not(feature = "f4"))] {
                for word in data {
                    let mut i = 0;

                    #[cfg(feature = "h5")]
                    while isr!(self.regs).read().txfe().bit_is_clear() {
                        i += 1;
                        if i >= MAX_ITERS {
                            // return Err(UartError::Hardware);
                        }
                    }

                    #[cfg(not(feature = "h5"))]
                    // Note: Per these PACs, TXFNF and TXE are on the same field, so this is actually
                    // checking txfnf if the fifo is enabled.
                    while isr!(self.regs).read().txe().bit_is_clear() {
                        i += 1;
                        if i >= MAX_ITERS {
                            return Err(UartError::Hardware);
                        }
                    }

                    self.regs
                        .tdr
                        .modify(|_, w| unsafe { w.tdr().bits(*word as u16) });
                }
                // 8. After writing the last data into the USART_TDR register, wait until TC=1. This indicates
                // that the transmission of the last frame is complete. This is required for instance when
                // the USART is disabled or enters the Halt mode to avoid corrupting the last
                // transmission
                let mut i = 0;
                while isr!(self.regs).read().tc().bit_is_clear() {
                        i += 1;
                        if i >= MAX_ITERS {
                            return Err(UartError::Hardware);
                        }
                }
            } else {
                for word in data {
                    let mut i = 0;
                    while self.regs.sr.read().txe().bit_is_clear() {
                        i += 1;
                        if i >= MAX_ITERS {
                            return Err(UartError::Hardware);
                        }
                    }
                    self.regs
                        .dr
                        .modify(|_, w| unsafe { w.dr().bits(*word as u16) });

                }
                let mut i = 0;
                while self.regs.sr.read().tc().bit_is_clear() {
                                            i += 1;
                        if i >= MAX_ITERS {
                            return Err(UartError::Hardware);
                        }
                }
            }
        }

        Ok(())
    }

    /// Write a single word, without waiting until ready for the next. Compared to the `write()` function, this
    /// does not block.
    pub fn write_one(&mut self, word: u8) {
        // todo: how does this work with a 9 bit words? Presumably you'd need to make `data`
        // todo take `&u16`.
        cfg_if! {
            if #[cfg(not(feature = "f4"))] {
            self.regs
                .tdr
                .modify(|_, w| unsafe { w.tdr().bits(word as u16) });
            } else {
                self.regs
                    .dr
                    .modify(|_, w| unsafe { w.dr().bits(word as u16) });
            }
        }
    }

    /// Receive data into a u8 buffer. See L44 RM, section 38.5.3: "Character reception procedure"
    pub fn read(&mut self, buf: &mut [u8]) -> Result<(), UartError> {
        for i in 0..buf.len() {
            let mut i_ = 0;
            cfg_if! {
                if #[cfg(not(feature = "f4"))] {
                    // Wait for the next bit

                    #[cfg(feature = "h5")]
                    while isr!(self.regs).read().rxfne().bit_is_clear() {
                        i_ += 1;
                        if i_ >= MAX_ITERS {
                            return Err(UartError::Hardware);
                        }
                    }

                    #[cfg(not(feature = "h5"))]
                    while isr!(self.regs).read().rxne().bit_is_clear() {
                        i_ += 1;
                        if i_ >= MAX_ITERS {
                            return Err(UartError::Hardware);
                        }
                    }

                    buf[i] = self.regs.rdr.read().rdr().bits() as u8;
                } else {
                    while self.regs.sr.read().rxne().bit_is_clear() {
                        i_ += 1;
                        if i_ >= MAX_ITERS {
                            return Err(UartError::Hardware);
                        }
                    }
                    buf[i] = self.regs.dr.read().dr().bits() as u8;
                }
            }
        }

        // When a character is received:
        // • The RXNE bit is set to indicate that the content of the shift register is transferred to the
        // RDR. In other words, data has been received and can be read (as well as its
        // associated error flags).
        // • An interrupt is generated if the RXNEIE bit is set.
        // • The error flags can be set if a frame error, noise or an overrun error has been detected
        // during reception. PE flag can also be set with RXNE.
        // • In multibuffer, RXNE is set after every byte received and is cleared by the DMA read of
        // the Receive data Register.
        // • In single buffer mode, clearing the RXNE bit is performed by a software read to the
        // USART_RDR register. The RXNE flag can also be cleared by writing 1 to the RXFRQ
        // in the USART_RQR register. The RXNE bit must be cleared before the end of the
        // reception of the next character to avoid an overrun error

        Ok(())
    }

    /// Read a single word, without waiting  until ready for the next. Compared to the `read()` function, this
    /// does not block.
    pub fn read_one(&mut self) -> u8 {
        cfg_if! {
            if #[cfg(not(feature = "f4"))] {
                self.regs.rdr.read().rdr().bits() as u8
            } else {
                self.regs.dr.read().dr().bits() as u8
            }
        }
    }

    #[cfg(not(any(feature = "f4", feature = "l552", feature = "h5")))]
    /// Transmit data using DMA. (L44 RM, section 38.5.15)
    /// Note that the `channel` argument is unused on F3 and L4, since it is hard-coded,
    /// and can't be configured using the DMAMUX peripheral. (`dma::mux()` fn).
    pub unsafe fn write_dma(
        &mut self,
        buf: &[u8],
        channel: DmaChannel,
        channel_cfg: ChannelCfg,
        dma_periph: dma::DmaPeriph,
    ) {
        let (ptr, len) = (buf.as_ptr(), buf.len());

        // To map a DMA channel for USART transmission, use
        // the following procedure (x denotes the channel number):

        #[cfg(any(feature = "f3", feature = "l4"))]
        let channel = R::write_chan();
        #[cfg(feature = "l4")]
        let mut dma_regs = unsafe { &(*DMA1::ptr()) }; // todo: Hardcoded DMA1
        #[cfg(feature = "l4")]
        R::write_sel(&mut dma_regs);

        #[cfg(feature = "h7")]
        let num_data = len as u32;
        #[cfg(not(feature = "h7"))]
        let num_data = len as u16;

        // "DMA mode can be enabled for transmission by setting DMAT bit in the USART_CR3
        // register. Data is loaded from a SRAM area configured using the DMA peripheral (refer to
        // Section 11: Direct memory access controller (DMA) on page 295) to the USART_TDR
        // register whenever the TXE bit is set."
        self.regs.cr3.modify(|_, w| w.dmat().set_bit());

        // 6. Clear the TC flag in the USART_ISR register by setting the TCCF bit in the
        // USART_ICR register.
        self.regs.icr.write(|w| w.tccf().set_bit());

        match dma_periph {
            dma::DmaPeriph::Dma1 => {
                let mut regs = unsafe { &(*DMA1::ptr()) };
                dma::cfg_channel(
                    &mut regs,
                    channel,
                    // 1. Write the USART_TDR register address in the DMA control register to configure it as
                    // the destination of the transfer. The data is moved to this address from memory after
                    // each TXE event.
                    &self.regs.tdr as *const _ as u32,
                    // 2. Write the memory address in the DMA control register to configure it as the source of
                    // the transfer. The data is loaded into the USART_TDR register from this memory area
                    // after each TXE event.
                    ptr as u32,
                    // 3. Configure the total number of bytes to be transferred to the DMA control register.
                    num_data,
                    dma::Direction::ReadFromMem,
                    // 4. Configure the channel priority in the DMA control register
                    // (Handled by `ChannelCfg::default())`
                    dma::DataSize::S8,
                    dma::DataSize::S8,
                    channel_cfg,
                );
            }
            #[cfg(not(any(feature = "f3x4", feature = "g0", feature = "wb")))]
            dma::DmaPeriph::Dma2 => {
                let mut regs = unsafe { &(*pac::DMA2::ptr()) };
                dma::cfg_channel(
                    &mut regs,
                    channel,
                    &self.regs.tdr as *const _ as u32,
                    ptr as u32,
                    num_data,
                    dma::Direction::ReadFromMem,
                    dma::DataSize::S8,
                    dma::DataSize::S8,
                    channel_cfg,
                );
            }
        }

        // 5. Configure DMA interrupt generation after half/ full transfer as required by the
        // application.
        // (Handled in `cfg_channel`)

        // 7. Activate the channel in the DMA register.
        // When the number of data transfers programmed in the DMA Controller is reached, the DMA
        // controller generates an interrupt on the DMA channel interrupt vector.
        // (Handled in `cfg_channel`)

        // In transmission mode, once the DMA has written all the data to be transmitted (the TCIF flag
        // is set in the DMA_ISR register), the TC flag can be monitored to make sure that the USART
        // communication is complete. This is required to avoid corrupting the last transmission before
        // disabling the USART or entering Stop mode. Software must wait until TC=1. The TC flag
        // remains cleared during all data transfers and it is set by hardware at the end of transmission
        // of the last frame.
    }

    #[cfg(not(any(feature = "f4", feature = "l552", feature = "h5")))]
    /// Receive data using DMA. (L44 RM, section 38.5.15; G4 RM section 37.5.19.
    /// Note that the `channel` argument is unused on F3 and L4, since it is hard-coded,
    /// and can't be configured using the DMAMUX peripheral. (`dma::mux()` fn).
    pub unsafe fn read_dma(
        &mut self,
        buf: &mut [u8],
        channel: DmaChannel,
        channel_cfg: ChannelCfg,
        dma_periph: dma::DmaPeriph,
    ) {
        let (ptr, len) = (buf.as_mut_ptr(), buf.len());

        #[cfg(any(feature = "f3", feature = "l4"))]
        let channel = R::read_chan();
        #[cfg(feature = "l4")]
        let mut dma_regs = unsafe { &(*DMA1::ptr()) }; // todo: Hardcoded DMA1
        #[cfg(feature = "l4")]
        R::write_sel(&mut dma_regs);

        #[cfg(feature = "h7")]
        let num_data = len as u32;
        #[cfg(not(feature = "h7"))]
        let num_data = len as u16;

        // DMA mode can be enabled for reception by setting the DMAR bit in USART_CR3 register.
        self.regs.cr3.modify(|_, w| w.dmar().set_bit());

        match dma_periph {
            dma::DmaPeriph::Dma1 => {
                let mut regs = unsafe { &(*DMA1::ptr()) };
                dma::cfg_channel(
                    &mut regs,
                    channel,
                    // 1. Write the USART_RDR register address in the DMA control register to configure it as
                    // the source of the transfer. The data is moved from this address to the memory after
                    // each RXNE event.
                    &self.regs.rdr as *const _ as u32,
                    // 2. Write the memory address in the DMA control register to configure it as the destination
                    // of the transfer. The data is loaded from USART_RDR to this memory area after each
                    // RXNE event.
                    ptr as u32,
                    // 3. Configure the total number of bytes to be transferred to the DMA control register.
                    num_data,
                    dma::Direction::ReadFromPeriph,
                    dma::DataSize::S8,
                    dma::DataSize::S8,
                    channel_cfg,
                );
            }
            #[cfg(not(any(feature = "f3x4", feature = "g0", feature = "wb")))]
            dma::DmaPeriph::Dma2 => {
                let mut regs = unsafe { &(*pac::DMA2::ptr()) };
                dma::cfg_channel(
                    &mut regs,
                    channel,
                    &self.regs.rdr as *const _ as u32,
                    ptr as u32,
                    num_data,
                    dma::Direction::ReadFromPeriph,
                    dma::DataSize::S8,
                    dma::DataSize::S8,
                    channel_cfg,
                );
            }
        }

        // 4. Configure the channel priority in the DMA control register
        // (Handled in cfg)

        // 5. Configure interrupt generation after half/ full transfer as required by the application.
        // (Handled by user code))

        // 6. Activate the channel in the DMA control register. (Handled by `cfg_channel` above).
        // When the number of data transfers programmed in the DMA Controller is reached, the DMA
        // controller generates an interrupt on the DMA channel interrupt vector.
        // (Handled in above fn call)

        // When the number of data transfers programmed in the DMA Controller is reached, the DMA
        // controller generates an interrupt on the DMA channel interrupt vector.
    }
    //
    // /// Flush the transmit buffer.
    // pub fn flush(&self) {
    //     #[cfg(not(feature = "f4"))]
    //     while isr!(self.regs).read().tc().bit_is_clear() {}
    //     #[cfg(feature = "f4")]
    //     while self.regs.sr.read().tc().bit_is_clear() {}
    // }

    #[cfg(not(feature = "f4"))]
    /// Enable a specific type of interrupt. See G4 RM, Table 349: USART interrupt requests.
    /// If `Some`, the inner value of `CharDetect` sets the address of the char to match.
    /// If `None`, the interrupt is enabled without changing the char to match.
    pub fn enable_interrupt(&mut self, interrupt: UsartInterrupt) {
        match interrupt {
            UsartInterrupt::CharDetect(char_wrapper) => {
                if let Some(char) = char_wrapper {
                    // Disable the UART to allow writing the `add` and `addm7` bits
                    cr1!(self.regs).modify(|_, w| w.ue().clear_bit());
                    while cr1!(self.regs).read().ue().bit_is_set() {}

                    // Enable character-detecting UART interrupt
                    cr1!(self.regs).modify(|_, w| w.cmie().set_bit());

                    // Allow an 8-bit address to be set in `add`.
                    self.regs.cr2.modify(|_, w| unsafe {
                        w.addm7().set_bit();
                        // Set the character to detect
                        cfg_if! {
                            if #[cfg(any(feature = "l5", feature = "g4", feature = "wb"))] {
                                w.add0_3().bits(char); // PAC error. Should be just like above. (?)
                                w.add4_7().bits(char >> 4)
                            } else {
                                w.add().bits(char)
                            // } else {
                            //     w.add().bits(char);
                            //     w.add4_7().bits(char >> 4)
                            }
                        }
                    });

                    cr1!(self.regs).modify(|_, w| w.ue().set_bit());
                    while cr1!(self.regs).read().ue().bit_is_clear() {}
                }

                cr1!(self.regs).modify(|_, w| w.cmie().set_bit());
            }
            UsartInterrupt::Cts => {
                self.regs.cr3.modify(|_, w| w.ctsie().set_bit());
            }
            UsartInterrupt::EndOfBlock => {
                cr1!(self.regs).modify(|_, w| w.eobie().set_bit());
            }
            UsartInterrupt::Idle => {
                cr1!(self.regs).modify(|_, w| w.idleie().set_bit());
            }
            UsartInterrupt::FramingError => {
                self.regs.cr3.modify(|_, w| w.eie().set_bit());
            }
            UsartInterrupt::LineBreak => {
                self.regs.cr2.modify(|_, w| w.lbdie().set_bit());
            }
            UsartInterrupt::Overrun => {
                self.regs.cr3.modify(|_, w| w.eie().set_bit());
            }
            UsartInterrupt::ParityError => {
                cr1!(self.regs).modify(|_, w| w.peie().set_bit());
            }
            UsartInterrupt::ReadNotEmpty => {
                #[cfg(feature = "h5")]
                cr1!(self.regs).modify(|_, w| w.rxfneie().set_bit());
                #[cfg(not(feature = "h5"))]
                cr1!(self.regs).modify(|_, w| w.rxneie().set_bit());
            }
            UsartInterrupt::ReceiverTimeout => {
                cr1!(self.regs).modify(|_, w| w.rtoie().set_bit());
            }
            #[cfg(not(any(feature = "f3", feature = "l4")))]
            UsartInterrupt::Tcbgt => {
                self.regs.cr3.modify(|_, w| w.tcbgtie().set_bit());
                self.regs.cr3.modify(|_, w| w.tcbgtie().set_bit());
            }
            UsartInterrupt::TransmissionComplete => {
                cr1!(self.regs).modify(|_, w| w.tcie().set_bit());
            }
            UsartInterrupt::TransmitEmpty => {
                #[cfg(feature = "h5")]
                cr1!(self.regs).modify(|_, w| w.txfeie().set_bit());
                #[cfg(not(feature = "h5"))]
                cr1!(self.regs).modify(|_, w| w.txeie().set_bit());
            }
        }
    }

    #[cfg(not(feature = "f4"))]
    /// Disable a specific type of interrupt. See G4 RM, Table 349: USART interrupt requests.
    /// Note that the inner value of `CharDetect` doesn't do anything here.
    pub fn disable_interrupt(&mut self, interrupt: UsartInterrupt) {
        match interrupt {
            UsartInterrupt::CharDetect(_) => {
                cr1!(self.regs).modify(|_, w| w.cmie().clear_bit());
            }
            UsartInterrupt::Cts => {
                self.regs.cr3.modify(|_, w| w.ctsie().clear_bit());
            }
            UsartInterrupt::EndOfBlock => {
                cr1!(self.regs).modify(|_, w| w.eobie().clear_bit());
            }
            UsartInterrupt::Idle => {
                cr1!(self.regs).modify(|_, w| w.idleie().clear_bit());
            }
            UsartInterrupt::FramingError => {
                self.regs.cr3.modify(|_, w| w.eie().clear_bit());
            }
            UsartInterrupt::LineBreak => {
                self.regs.cr2.modify(|_, w| w.lbdie().clear_bit());
            }
            UsartInterrupt::Overrun => {
                self.regs.cr3.modify(|_, w| w.eie().clear_bit());
            }
            UsartInterrupt::ParityError => {
                cr1!(self.regs).modify(|_, w| w.peie().clear_bit());
            }
            UsartInterrupt::ReadNotEmpty => {
                #[cfg(feature = "h5")]
                cr1!(self.regs).modify(|_, w| w.rxfneie().clear_bit());
                #[cfg(not(feature = "h5"))]
                cr1!(self.regs).modify(|_, w| w.rxneie().clear_bit());
            }
            UsartInterrupt::ReceiverTimeout => {
                cr1!(self.regs).modify(|_, w| w.rtoie().clear_bit());
            }
            #[cfg(not(any(feature = "f3", feature = "l4")))]
            UsartInterrupt::Tcbgt => {
                self.regs.cr3.modify(|_, w| w.tcbgtie().clear_bit());
                self.regs.cr3.modify(|_, w| w.tcbgtie().clear_bit());
            }
            UsartInterrupt::TransmissionComplete => {
                cr1!(self.regs).modify(|_, w| w.tcie().clear_bit());
            }
            UsartInterrupt::TransmitEmpty => {
                #[cfg(feature = "h5")]
                cr1!(self.regs).modify(|_, w| w.txfeie().clear_bit());
                #[cfg(not(feature = "h5"))]
                cr1!(self.regs).modify(|_, w| w.txeie().clear_bit());
            }
        }
    }

    #[cfg(not(feature = "f4"))]
    /// Print the (raw) contents of the status register.
    pub fn read_status(&self) -> u32 {
        unsafe { isr!(self.regs).read().bits() }
    }

    #[cfg(not(feature = "f4"))]
    /// Clears the interrupt pending flag for a specific type of interrupt. Note that
    /// it can also clear error flags, like Overrun and framing errors. See G4 RM,
    /// Table 349: USART interrupt requests.
    /// Note that the inner value of `CharDetect` doesn't do anything here.
    pub fn clear_interrupt(&mut self, interrupt: UsartInterrupt) {
        match interrupt {
            UsartInterrupt::CharDetect(_) => self.regs.icr.write(|w| w.cmcf().set_bit()),
            UsartInterrupt::Cts => self.regs.icr.write(|w| w.ctscf().set_bit()),
            UsartInterrupt::EndOfBlock => self.regs.icr.write(|w| w.eobcf().set_bit()),
            UsartInterrupt::Idle => self.regs.icr.write(|w| w.idlecf().set_bit()),
            UsartInterrupt::FramingError => self.regs.icr.write(|w| w.fecf().set_bit()),
            UsartInterrupt::LineBreak => self.regs.icr.write(|w| w.lbdcf().set_bit()),
            UsartInterrupt::Overrun => self.regs.icr.write(|w| w.orecf().set_bit()),
            UsartInterrupt::ParityError => self.regs.icr.write(|w| w.pecf().set_bit()),
            UsartInterrupt::ReadNotEmpty => self.regs.rqr.write(|w| w.rxfrq().set_bit()),
            UsartInterrupt::ReceiverTimeout => self.regs.icr.write(|w| w.rtocf().set_bit()),
            #[cfg(not(any(feature = "f3", feature = "l4", feature = "h7")))]
            UsartInterrupt::Tcbgt => self.regs.icr.write(|w| w.tcbgtcf().set_bit()),
            #[cfg(feature = "h7")]
            UsartInterrupt::Tcbgt => self.regs.icr.write(|w| w.tcbgtc().set_bit()),
            UsartInterrupt::TransmissionComplete => self.regs.icr.write(|w| w.tccf().set_bit()),
            UsartInterrupt::TransmitEmpty => self.regs.rqr.write(|w| w.txfrq().set_bit()),
        }
    }

    #[cfg(not(feature = "f4"))]
    /// Checks if a given status flag is set. Returns `true` if the status flag is set. Note that this preforms
    /// a read each time called. If checking multiple flags, this isn't optimal.
    pub fn check_status_flag(&mut self, flag: UsartInterrupt) -> bool {
        let status = isr!(self.regs).read();

        match flag {
            UsartInterrupt::CharDetect(_) => status.cmf().bit_is_set(),
            UsartInterrupt::Cts => status.cts().bit_is_set(),
            UsartInterrupt::EndOfBlock => status.eobf().bit_is_set(),
            UsartInterrupt::Idle => status.idle().bit_is_set(),
            UsartInterrupt::FramingError => status.fe().bit_is_set(),
            UsartInterrupt::LineBreak => status.lbdf().bit_is_set(),
            UsartInterrupt::Overrun => status.ore().bit_is_set(),
            UsartInterrupt::ParityError => status.pe().bit_is_set(),
            #[cfg(feature = "h5")]
            UsartInterrupt::ReadNotEmpty => status.rxfne().bit_is_set(),
            #[cfg(not(feature = "h5"))]
            UsartInterrupt::ReadNotEmpty => status.rxne().bit_is_set(),
            UsartInterrupt::ReceiverTimeout => status.rtof().bit_is_set(),
            #[cfg(not(any(feature = "f3", feature = "l4")))]
            UsartInterrupt::Tcbgt => status.tcbgt().bit_is_set(),
            UsartInterrupt::TransmissionComplete => status.tc().bit_is_set(),
            #[cfg(feature = "h5")]
            UsartInterrupt::TransmitEmpty => status.txfe().bit_is_set(),
            #[cfg(not(feature = "h5"))]
            UsartInterrupt::TransmitEmpty => status.txe().bit_is_set(),
        }
    }
}

// todo: Use those errors above.
//
// #[cfg(feature = "embedded_hal")]
// impl<R> Read<u8> for Usart<R>
// where
//     R: Deref<Target = pac::usart1::RegisterBlock> + RccPeriph + BaudPeriph,
// {
//     type Error = Error;
//
//     #[cfg(not(feature = "f4"))]
//     fn read(&mut self) -> nb::Result<u8, UartError> {
//         while !isr!(self.regs).read().rxne().bit_is_set() {}
//
//         Ok(self.regs.rdr.read().rdr().bits() as u8)
//     }
//
//     #[cfg(feature = "f4")]
//     fn read(&mut self) -> nb::Result<u8, UartError> {
//         Ok(Usart::read_one(self))
//     }
// }
//
// #[cfg(feature = "embedded_hal")]
// impl<R> Write<u8> for Usart<R>
// where
//     R: Deref<Target = pac::usart1::RegisterBlock> + RccPeriph + BaudPeriph,
// {
//     type Error = Error;
//
//     #[cfg(not(feature = "f4"))]
//     fn write(&mut self, word: u8) -> nb::Result<(), UartError> {
//         while !isr!(self.regs).read().txe().bit_is_set() {}
//
//         self.regs
//             .tdr
//             .modify(|_, w| unsafe { w.tdr().bits(word as u16) });
//
//         Ok(())
//     }
//
//     #[cfg(feature = "f4")]
//     fn write(&mut self, word: u8) -> nb::Result<(), UartError> {
//         while !self.regs.sr.read().txe().bit_is_set() {}
//
//         self.regs
//             .dr
//             .modify(|_, w| unsafe { w.dr().bits(word as u16) });
//
//         Ok(())
//     }
//
//     fn flush(&mut self) -> nb::Result<(), UartError> {
//         #[cfg(not(feature = "f4"))]
//         while !isr!(self.regs).read().tc().bit_is_set() {}
//         #[cfg(feature = "f4")]
//         while !self.regs.sr.read().tc().bit_is_set() {}
//
//         Ok(())
//     }
// }
//
// #[cfg(feature = "embedded_hal")]
// // #[cfg_attr(docsrs, doc(cfg(feature = "embedded_hal")))]
// impl<R> blocking::serial::Write<u8> for Usart<R>
// where
//     R: Deref<Target = pac::usart1::RegisterBlock> + RccPeriph + BaudPeriph,
// {
//     type Error = Error;
//
//     fn bwrite_all(&mut self, buffer: &[u8]) -> Result<(), UartError> {
//         Usart::write(self, buffer);
//         Ok(())
//     }
//
//     fn bflush(&mut self) -> Result<(), UartError> {
//         Self::flush(self);
//
//         Ok(())
//     }
// }