| // Copyright 2024, Linaro Limited |
| // Author(s): Manos Pitsidianakis <manos.pitsidianakis@linaro.org> |
| // SPDX-License-Identifier: GPL-2.0-or-later |
| // |
| // PL011 QEMU Device Model |
| // |
| // This library implements a device model for the PrimeCell® UART (PL011) |
| // device in QEMU. |
| // |
| #![doc = include_str!("../README.md")] |
| //! # Library crate |
| //! |
| //! See [`PL011State`](crate::device::PL011State) for the device model type and |
| //! the [`registers`] module for register types. |
| |
| #![deny( |
| rustdoc::broken_intra_doc_links, |
| rustdoc::redundant_explicit_links, |
| clippy::correctness, |
| clippy::suspicious, |
| clippy::complexity, |
| clippy::perf, |
| clippy::cargo, |
| clippy::nursery, |
| clippy::style, |
| // restriction group |
| clippy::dbg_macro, |
| clippy::as_underscore, |
| clippy::assertions_on_result_states, |
| // pedantic group |
| clippy::doc_markdown, |
| clippy::borrow_as_ptr, |
| clippy::cast_lossless, |
| clippy::option_if_let_else, |
| clippy::missing_const_for_fn, |
| clippy::cognitive_complexity, |
| clippy::missing_safety_doc, |
| )] |
| #![allow(clippy::result_unit_err)] |
| |
| extern crate bilge; |
| extern crate bilge_impl; |
| extern crate qemu_api; |
| |
| pub mod device; |
| pub mod device_class; |
| pub mod memory_ops; |
| |
| pub const TYPE_PL011: &::core::ffi::CStr = c"pl011"; |
| pub const TYPE_PL011_LUMINARY: &::core::ffi::CStr = c"pl011_luminary"; |
| |
| /// Offset of each register from the base memory address of the device. |
| /// |
| /// # Source |
| /// ARM DDI 0183G, Table 3-1 p.3-3 |
| #[doc(alias = "offset")] |
| #[allow(non_camel_case_types)] |
| #[repr(u64)] |
| #[derive(Debug)] |
| pub enum RegisterOffset { |
| /// Data Register |
| /// |
| /// A write to this register initiates the actual data transmission |
| #[doc(alias = "UARTDR")] |
| DR = 0x000, |
| /// Receive Status Register or Error Clear Register |
| #[doc(alias = "UARTRSR")] |
| #[doc(alias = "UARTECR")] |
| RSR = 0x004, |
| /// Flag Register |
| /// |
| /// A read of this register shows if transmission is complete |
| #[doc(alias = "UARTFR")] |
| FR = 0x018, |
| /// Fractional Baud Rate Register |
| /// |
| /// responsible for baud rate speed |
| #[doc(alias = "UARTFBRD")] |
| FBRD = 0x028, |
| /// `IrDA` Low-Power Counter Register |
| #[doc(alias = "UARTILPR")] |
| ILPR = 0x020, |
| /// Integer Baud Rate Register |
| /// |
| /// Responsible for baud rate speed |
| #[doc(alias = "UARTIBRD")] |
| IBRD = 0x024, |
| /// line control register (data frame format) |
| #[doc(alias = "UARTLCR_H")] |
| LCR_H = 0x02C, |
| /// Toggle UART, transmission or reception |
| #[doc(alias = "UARTCR")] |
| CR = 0x030, |
| /// Interrupt FIFO Level Select Register |
| #[doc(alias = "UARTIFLS")] |
| FLS = 0x034, |
| /// Interrupt Mask Set/Clear Register |
| #[doc(alias = "UARTIMSC")] |
| IMSC = 0x038, |
| /// Raw Interrupt Status Register |
| #[doc(alias = "UARTRIS")] |
| RIS = 0x03C, |
| /// Masked Interrupt Status Register |
| #[doc(alias = "UARTMIS")] |
| MIS = 0x040, |
| /// Interrupt Clear Register |
| #[doc(alias = "UARTICR")] |
| ICR = 0x044, |
| /// DMA control Register |
| #[doc(alias = "UARTDMACR")] |
| DMACR = 0x048, |
| ///// Reserved, offsets `0x04C` to `0x07C`. |
| //Reserved = 0x04C, |
| } |
| |
| impl core::convert::TryFrom<u64> for RegisterOffset { |
| type Error = u64; |
| |
| fn try_from(value: u64) -> Result<Self, Self::Error> { |
| macro_rules! case { |
| ($($discriminant:ident),*$(,)*) => { |
| /* check that matching on all macro arguments compiles, which means we are not |
| * missing any enum value; if the type definition ever changes this will stop |
| * compiling. |
| */ |
| const fn _assert_exhaustive(val: RegisterOffset) { |
| match val { |
| $(RegisterOffset::$discriminant => (),)* |
| } |
| } |
| |
| match value { |
| $(x if x == Self::$discriminant as u64 => Ok(Self::$discriminant),)* |
| _ => Err(value), |
| } |
| } |
| } |
| case! { DR, RSR, FR, FBRD, ILPR, IBRD, LCR_H, CR, FLS, IMSC, RIS, MIS, ICR, DMACR } |
| } |
| } |
| |
| pub mod registers { |
| //! Device registers exposed as typed structs which are backed by arbitrary |
| //! integer bitmaps. [`Data`], [`Control`], [`LineControl`], etc. |
| //! |
| //! All PL011 registers are essentially 32-bit wide, but are typed here as |
| //! bitmaps with only the necessary width. That is, if a struct bitmap |
| //! in this module is for example 16 bits long, it should be conceived |
| //! as a 32-bit register where the unmentioned higher bits are always |
| //! unused thus treated as zero when read or written. |
| use bilge::prelude::*; |
| |
| // TODO: FIFO Mode has different semantics |
| /// Data Register, `UARTDR` |
| /// |
| /// The `UARTDR` register is the data register. |
| /// |
| /// For words to be transmitted: |
| /// |
| /// - if the FIFOs are enabled, data written to this location is pushed onto |
| /// the transmit |
| /// FIFO |
| /// - if the FIFOs are not enabled, data is stored in the transmitter |
| /// holding register (the |
| /// bottom word of the transmit FIFO). |
| /// |
| /// The write operation initiates transmission from the UART. The data is |
| /// prefixed with a start bit, appended with the appropriate parity bit |
| /// (if parity is enabled), and a stop bit. The resultant word is then |
| /// transmitted. |
| /// |
| /// For received words: |
| /// |
| /// - if the FIFOs are enabled, the data byte and the 4-bit status (break, |
| /// frame, parity, |
| /// and overrun) is pushed onto the 12-bit wide receive FIFO |
| /// - if the FIFOs are not enabled, the data byte and status are stored in |
| /// the receiving |
| /// holding register (the bottom word of the receive FIFO). |
| /// |
| /// The received data byte is read by performing reads from the `UARTDR` |
| /// register along with the corresponding status information. The status |
| /// information can also be read by a read of the `UARTRSR/UARTECR` |
| /// register. |
| /// |
| /// # Note |
| /// |
| /// You must disable the UART before any of the control registers are |
| /// reprogrammed. When the UART is disabled in the middle of |
| /// transmission or reception, it completes the current character before |
| /// stopping. |
| /// |
| /// # Source |
| /// ARM DDI 0183G 3.3.1 Data Register, UARTDR |
| #[bitsize(16)] |
| #[derive(Clone, Copy, DebugBits, FromBits)] |
| #[doc(alias = "UARTDR")] |
| pub struct Data { |
| _reserved: u4, |
| pub data: u8, |
| pub framing_error: bool, |
| pub parity_error: bool, |
| pub break_error: bool, |
| pub overrun_error: bool, |
| } |
| |
| // TODO: FIFO Mode has different semantics |
| /// Receive Status Register / Error Clear Register, `UARTRSR/UARTECR` |
| /// |
| /// The UARTRSR/UARTECR register is the receive status register/error clear |
| /// register. Receive status can also be read from the `UARTRSR` |
| /// register. If the status is read from this register, then the status |
| /// information for break, framing and parity corresponds to the |
| /// data character read from the [Data register](Data), `UARTDR` prior to |
| /// reading the UARTRSR register. The status information for overrun is |
| /// set immediately when an overrun condition occurs. |
| /// |
| /// |
| /// # Note |
| /// The received data character must be read first from the [Data |
| /// Register](Data), `UARTDR` before reading the error status associated |
| /// with that data character from the `UARTRSR` register. This read |
| /// sequence cannot be reversed, because the `UARTRSR` register is |
| /// updated only when a read occurs from the `UARTDR` register. However, |
| /// the status information can also be obtained by reading the `UARTDR` |
| /// register |
| /// |
| /// # Source |
| /// ARM DDI 0183G 3.3.2 Receive Status Register/Error Clear Register, |
| /// UARTRSR/UARTECR |
| #[bitsize(8)] |
| #[derive(Clone, Copy, DebugBits, FromBits)] |
| pub struct ReceiveStatusErrorClear { |
| pub framing_error: bool, |
| pub parity_error: bool, |
| pub break_error: bool, |
| pub overrun_error: bool, |
| _reserved_unpredictable: u4, |
| } |
| |
| impl ReceiveStatusErrorClear { |
| pub fn reset(&mut self) { |
| // All the bits are cleared to 0 on reset. |
| *self = 0.into(); |
| } |
| } |
| |
| impl Default for ReceiveStatusErrorClear { |
| fn default() -> Self { |
| 0.into() |
| } |
| } |
| |
| #[bitsize(16)] |
| #[derive(Clone, Copy, DebugBits, FromBits)] |
| /// Flag Register, `UARTFR` |
| #[doc(alias = "UARTFR")] |
| pub struct Flags { |
| /// CTS Clear to send. This bit is the complement of the UART clear to |
| /// send, `nUARTCTS`, modem status input. That is, the bit is 1 |
| /// when `nUARTCTS` is LOW. |
| pub clear_to_send: bool, |
| /// DSR Data set ready. This bit is the complement of the UART data set |
| /// ready, `nUARTDSR`, modem status input. That is, the bit is 1 when |
| /// `nUARTDSR` is LOW. |
| pub data_set_ready: bool, |
| /// DCD Data carrier detect. This bit is the complement of the UART data |
| /// carrier detect, `nUARTDCD`, modem status input. That is, the bit is |
| /// 1 when `nUARTDCD` is LOW. |
| pub data_carrier_detect: bool, |
| /// BUSY UART busy. If this bit is set to 1, the UART is busy |
| /// transmitting data. This bit remains set until the complete |
| /// byte, including all the stop bits, has been sent from the |
| /// shift register. This bit is set as soon as the transmit FIFO |
| /// becomes non-empty, regardless of whether the UART is enabled |
| /// or not. |
| pub busy: bool, |
| /// RXFE Receive FIFO empty. The meaning of this bit depends on the |
| /// state of the FEN bit in the UARTLCR_H register. If the FIFO |
| /// is disabled, this bit is set when the receive holding |
| /// register is empty. If the FIFO is enabled, the RXFE bit is |
| /// set when the receive FIFO is empty. |
| pub receive_fifo_empty: bool, |
| /// TXFF Transmit FIFO full. The meaning of this bit depends on the |
| /// state of the FEN bit in the UARTLCR_H register. If the FIFO |
| /// is disabled, this bit is set when the transmit holding |
| /// register is full. If the FIFO is enabled, the TXFF bit is |
| /// set when the transmit FIFO is full. |
| pub transmit_fifo_full: bool, |
| /// RXFF Receive FIFO full. The meaning of this bit depends on the state |
| /// of the FEN bit in the UARTLCR_H register. If the FIFO is |
| /// disabled, this bit is set when the receive holding register |
| /// is full. If the FIFO is enabled, the RXFF bit is set when |
| /// the receive FIFO is full. |
| pub receive_fifo_full: bool, |
| /// Transmit FIFO empty. The meaning of this bit depends on the state of |
| /// the FEN bit in the [Line Control register](LineControl), |
| /// `UARTLCR_H`. If the FIFO is disabled, this bit is set when the |
| /// transmit holding register is empty. If the FIFO is enabled, |
| /// the TXFE bit is set when the transmit FIFO is empty. This |
| /// bit does not indicate if there is data in the transmit shift |
| /// register. |
| pub transmit_fifo_empty: bool, |
| /// `RI`, is `true` when `nUARTRI` is `LOW`. |
| pub ring_indicator: bool, |
| _reserved_zero_no_modify: u7, |
| } |
| |
| impl Flags { |
| pub fn reset(&mut self) { |
| // After reset TXFF, RXFF, and BUSY are 0, and TXFE and RXFE are 1 |
| self.set_receive_fifo_full(false); |
| self.set_transmit_fifo_full(false); |
| self.set_busy(false); |
| self.set_receive_fifo_empty(true); |
| self.set_transmit_fifo_empty(true); |
| } |
| } |
| |
| impl Default for Flags { |
| fn default() -> Self { |
| let mut ret: Self = 0.into(); |
| ret.reset(); |
| ret |
| } |
| } |
| |
| #[bitsize(16)] |
| #[derive(Clone, Copy, DebugBits, FromBits)] |
| /// Line Control Register, `UARTLCR_H` |
| #[doc(alias = "UARTLCR_H")] |
| pub struct LineControl { |
| /// 15:8 - Reserved, do not modify, read as zero. |
| _reserved_zero_no_modify: u8, |
| /// 7 SPS Stick parity select. |
| /// 0 = stick parity is disabled |
| /// 1 = either: |
| /// • if the EPS bit is 0 then the parity bit is transmitted and checked |
| /// as a 1 • if the EPS bit is 1 then the parity bit is |
| /// transmitted and checked as a 0. This bit has no effect when |
| /// the PEN bit disables parity checking and generation. See Table 3-11 |
| /// on page 3-14 for the parity truth table. |
| pub sticky_parity: bool, |
| /// WLEN Word length. These bits indicate the number of data bits |
| /// transmitted or received in a frame as follows: b11 = 8 bits |
| /// b10 = 7 bits |
| /// b01 = 6 bits |
| /// b00 = 5 bits. |
| pub word_length: WordLength, |
| /// FEN Enable FIFOs: |
| /// 0 = FIFOs are disabled (character mode) that is, the FIFOs become |
| /// 1-byte-deep holding registers 1 = transmit and receive FIFO |
| /// buffers are enabled (FIFO mode). |
| pub fifos_enabled: Mode, |
| /// 3 STP2 Two stop bits select. If this bit is set to 1, two stop bits |
| /// are transmitted at the end of the frame. The receive |
| /// logic does not check for two stop bits being received. |
| pub two_stops_bits: bool, |
| /// EPS Even parity select. Controls the type of parity the UART uses |
| /// during transmission and reception: |
| /// - 0 = odd parity. The UART generates or checks for an odd number of |
| /// 1s in the data and parity bits. |
| /// - 1 = even parity. The UART generates or checks for an even number |
| /// of 1s in the data and parity bits. |
| /// This bit has no effect when the `PEN` bit disables parity checking |
| /// and generation. See Table 3-11 on page 3-14 for the parity |
| /// truth table. |
| pub parity: Parity, |
| /// 1 PEN Parity enable: |
| /// |
| /// - 0 = parity is disabled and no parity bit added to the data frame |
| /// - 1 = parity checking and generation is enabled. |
| /// |
| /// See Table 3-11 on page 3-14 for the parity truth table. |
| pub parity_enabled: bool, |
| /// BRK Send break. |
| /// |
| /// If this bit is set to `1`, a low-level is continually output on the |
| /// `UARTTXD` output, after completing transmission of the |
| /// current character. For the proper execution of the break command, |
| /// the software must set this bit for at least two complete |
| /// frames. For normal use, this bit must be cleared to `0`. |
| pub send_break: bool, |
| } |
| |
| impl LineControl { |
| pub fn reset(&mut self) { |
| // All the bits are cleared to 0 when reset. |
| *self = 0.into(); |
| } |
| } |
| |
| impl Default for LineControl { |
| fn default() -> Self { |
| 0.into() |
| } |
| } |
| |
| #[bitsize(1)] |
| #[derive(Clone, Copy, Debug, Eq, FromBits, PartialEq)] |
| /// `EPS` "Even parity select", field of [Line Control |
| /// register](LineControl). |
| pub enum Parity { |
| /// - 0 = odd parity. The UART generates or checks for an odd number of |
| /// 1s in the data and parity bits. |
| Odd = 0, |
| /// - 1 = even parity. The UART generates or checks for an even number |
| /// of 1s in the data and parity bits. |
| Even = 1, |
| } |
| |
| #[bitsize(1)] |
| #[derive(Clone, Copy, Debug, Eq, FromBits, PartialEq)] |
| /// `FEN` "Enable FIFOs" or Device mode, field of [Line Control |
| /// register](LineControl). |
| pub enum Mode { |
| /// 0 = FIFOs are disabled (character mode) that is, the FIFOs become |
| /// 1-byte-deep holding registers |
| Character = 0, |
| /// 1 = transmit and receive FIFO buffers are enabled (FIFO mode). |
| FIFO = 1, |
| } |
| |
| impl From<Mode> for bool { |
| fn from(val: Mode) -> Self { |
| matches!(val, Mode::FIFO) |
| } |
| } |
| |
| #[bitsize(2)] |
| #[derive(Clone, Copy, Debug, Eq, FromBits, PartialEq)] |
| /// `WLEN` Word length, field of [Line Control register](LineControl). |
| /// |
| /// These bits indicate the number of data bits transmitted or received in a |
| /// frame as follows: |
| pub enum WordLength { |
| /// b11 = 8 bits |
| _8Bits = 0b11, |
| /// b10 = 7 bits |
| _7Bits = 0b10, |
| /// b01 = 6 bits |
| _6Bits = 0b01, |
| /// b00 = 5 bits. |
| _5Bits = 0b00, |
| } |
| |
| /// Control Register, `UARTCR` |
| /// |
| /// The `UARTCR` register is the control register. All the bits are cleared |
| /// to `0` on reset except for bits `9` and `8` that are set to `1`. |
| /// |
| /// # Source |
| /// ARM DDI 0183G, 3.3.8 Control Register, `UARTCR`, Table 3-12 |
| #[bitsize(16)] |
| #[doc(alias = "UARTCR")] |
| #[derive(Clone, Copy, DebugBits, FromBits)] |
| pub struct Control { |
| /// `UARTEN` UART enable: 0 = UART is disabled. If the UART is disabled |
| /// in the middle of transmission or reception, it completes the current |
| /// character before stopping. 1 = the UART is enabled. Data |
| /// transmission and reception occurs for either UART signals or SIR |
| /// signals depending on the setting of the SIREN bit. |
| pub enable_uart: bool, |
| /// `SIREN` `SIR` enable: 0 = IrDA SIR ENDEC is disabled. `nSIROUT` |
| /// remains LOW (no light pulse generated), and signal transitions on |
| /// SIRIN have no effect. 1 = IrDA SIR ENDEC is enabled. Data is |
| /// transmitted and received on nSIROUT and SIRIN. UARTTXD remains HIGH, |
| /// in the marking state. Signal transitions on UARTRXD or modem status |
| /// inputs have no effect. This bit has no effect if the UARTEN bit |
| /// disables the UART. |
| pub enable_sir: bool, |
| /// `SIRLP` SIR low-power IrDA mode. This bit selects the IrDA encoding |
| /// mode. If this bit is cleared to 0, low-level bits are transmitted as |
| /// an active high pulse with a width of 3/ 16th of the bit period. If |
| /// this bit is set to 1, low-level bits are transmitted with a pulse |
| /// width that is 3 times the period of the IrLPBaud16 input signal, |
| /// regardless of the selected bit rate. Setting this bit uses less |
| /// power, but might reduce transmission distances. |
| pub sir_lowpower_irda_mode: u1, |
| /// Reserved, do not modify, read as zero. |
| _reserved_zero_no_modify: u4, |
| /// `LBE` Loopback enable. If this bit is set to 1 and the SIREN bit is |
| /// set to 1 and the SIRTEST bit in the Test Control register, UARTTCR |
| /// on page 4-5 is set to 1, then the nSIROUT path is inverted, and fed |
| /// through to the SIRIN path. The SIRTEST bit in the test register must |
| /// be set to 1 to override the normal half-duplex SIR operation. This |
| /// must be the requirement for accessing the test registers during |
| /// normal operation, and SIRTEST must be cleared to 0 when loopback |
| /// testing is finished. This feature reduces the amount of external |
| /// coupling required during system test. If this bit is set to 1, and |
| /// the SIRTEST bit is set to 0, the UARTTXD path is fed through to the |
| /// UARTRXD path. In either SIR mode or UART mode, when this bit is set, |
| /// the modem outputs are also fed through to the modem inputs. This bit |
| /// is cleared to 0 on reset, to disable loopback. |
| pub enable_loopback: bool, |
| /// `TXE` Transmit enable. If this bit is set to 1, the transmit section |
| /// of the UART is enabled. Data transmission occurs for either UART |
| /// signals, or SIR signals depending on the setting of the SIREN bit. |
| /// When the UART is disabled in the middle of transmission, it |
| /// completes the current character before stopping. |
| pub enable_transmit: bool, |
| /// `RXE` Receive enable. If this bit is set to 1, the receive section |
| /// of the UART is enabled. Data reception occurs for either UART |
| /// signals or SIR signals depending on the setting of the SIREN bit. |
| /// When the UART is disabled in the middle of reception, it completes |
| /// the current character before stopping. |
| pub enable_receive: bool, |
| /// `DTR` Data transmit ready. This bit is the complement of the UART |
| /// data transmit ready, `nUARTDTR`, modem status output. That is, when |
| /// the bit is programmed to a 1 then `nUARTDTR` is LOW. |
| pub data_transmit_ready: bool, |
| /// `RTS` Request to send. This bit is the complement of the UART |
| /// request to send, `nUARTRTS`, modem status output. That is, when the |
| /// bit is programmed to a 1 then `nUARTRTS` is LOW. |
| pub request_to_send: bool, |
| /// `Out1` This bit is the complement of the UART Out1 (`nUARTOut1`) |
| /// modem status output. That is, when the bit is programmed to a 1 the |
| /// output is 0. For DTE this can be used as Data Carrier Detect (DCD). |
| pub out_1: bool, |
| /// `Out2` This bit is the complement of the UART Out2 (`nUARTOut2`) |
| /// modem status output. That is, when the bit is programmed to a 1, the |
| /// output is 0. For DTE this can be used as Ring Indicator (RI). |
| pub out_2: bool, |
| /// `RTSEn` RTS hardware flow control enable. If this bit is set to 1, |
| /// RTS hardware flow control is enabled. Data is only requested when |
| /// there is space in the receive FIFO for it to be received. |
| pub rts_hardware_flow_control_enable: bool, |
| /// `CTSEn` CTS hardware flow control enable. If this bit is set to 1, |
| /// CTS hardware flow control is enabled. Data is only transmitted when |
| /// the `nUARTCTS` signal is asserted. |
| pub cts_hardware_flow_control_enable: bool, |
| } |
| |
| impl Control { |
| pub fn reset(&mut self) { |
| *self = 0.into(); |
| self.set_enable_receive(true); |
| self.set_enable_transmit(true); |
| } |
| } |
| |
| impl Default for Control { |
| fn default() -> Self { |
| let mut ret: Self = 0.into(); |
| ret.reset(); |
| ret |
| } |
| } |
| |
| /// Interrupt status bits in UARTRIS, UARTMIS, UARTIMSC |
| pub const INT_OE: u32 = 1 << 10; |
| pub const INT_BE: u32 = 1 << 9; |
| pub const INT_PE: u32 = 1 << 8; |
| pub const INT_FE: u32 = 1 << 7; |
| pub const INT_RT: u32 = 1 << 6; |
| pub const INT_TX: u32 = 1 << 5; |
| pub const INT_RX: u32 = 1 << 4; |
| pub const INT_DSR: u32 = 1 << 3; |
| pub const INT_DCD: u32 = 1 << 2; |
| pub const INT_CTS: u32 = 1 << 1; |
| pub const INT_RI: u32 = 1 << 0; |
| pub const INT_E: u32 = INT_OE | INT_BE | INT_PE | INT_FE; |
| pub const INT_MS: u32 = INT_RI | INT_DSR | INT_DCD | INT_CTS; |
| |
| #[repr(u32)] |
| pub enum Interrupt { |
| OE = 1 << 10, |
| BE = 1 << 9, |
| PE = 1 << 8, |
| FE = 1 << 7, |
| RT = 1 << 6, |
| TX = 1 << 5, |
| RX = 1 << 4, |
| DSR = 1 << 3, |
| DCD = 1 << 2, |
| CTS = 1 << 1, |
| RI = 1 << 0, |
| } |
| |
| impl Interrupt { |
| pub const E: u32 = INT_OE | INT_BE | INT_PE | INT_FE; |
| pub const MS: u32 = INT_RI | INT_DSR | INT_DCD | INT_CTS; |
| } |
| } |
| |
| // TODO: You must disable the UART before any of the control registers are |
| // reprogrammed. When the UART is disabled in the middle of transmission or |
| // reception, it completes the current character before stopping |