From: Peter Maydell Date: Wed, 14 May 2025 13:29:47 +0000 (+0100) Subject: rust: pl011: Cut down amount of text quoted from PL011 TRM X-Git-Tag: v10.1.0-rc0~85^2~50 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=6414b7709d404bf410da360bab865133832ade85;p=thirdparty%2Fqemu.git rust: pl011: Cut down amount of text quoted from PL011 TRM Currently the comments in the Rust pl011 register.rs file include large amounts of text from the PL011 TRM. This is much more commentary than we typically quote from a device reference manual, and much of it is not relevant to QEMU. Compress and rephrase the comments so that we are not quoting such a large volume of TRM text. We add a URL for the TRM; readers who need more detail on the function of the register bits can find it there, presented in context with the overall description of the hardware. Signed-off-by: Peter Maydell Reviewed-by: Daniel P. Berrangé --- diff --git a/rust/hw/char/pl011/src/registers.rs b/rust/hw/char/pl011/src/registers.rs index cd92fa2c300..690feb63785 100644 --- a/rust/hw/char/pl011/src/registers.rs +++ b/rust/hw/char/pl011/src/registers.rs @@ -5,13 +5,13 @@ //! Device registers exposed as typed structs which are backed by arbitrary //! integer bitmaps. [`Data`], [`Control`], [`LineControl`], etc. +// For more detail see the PL011 Technical Reference Manual DDI0183: +// https://developer.arm.com/documentation/ddi0183/latest/ + use bilge::prelude::*; use qemu_api::impl_vmstate_bitsized; /// 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)] @@ -87,48 +87,11 @@ pub struct Errors { _reserved_unpredictable: u4, } -// 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 +/// The `UARTDR` register is the data register; write for TX and +/// read for RX. It is a 12-bit register, where bits 7..0 are the +/// character and bits 11..8 are error bits. #[bitsize(32)] #[derive(Clone, Copy, Default, DebugBits, FromBits)] #[doc(alias = "UARTDR")] @@ -144,30 +107,17 @@ impl Data { pub const BREAK: Self = Self { value: 1 << 10 }; } -// 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 +/// This register provides a different way to read the four receive +/// status error bits that can be found in bits 11..8 of the UARTDR +/// on a read. It gets updated when the guest reads UARTDR, and the +/// status bits correspond to that character that was just read. /// -/// # Source -/// ARM DDI 0183G 3.3.2 Receive Status Register/Error Clear Register, -/// UARTRSR/UARTECR +/// The TRM confusingly describes this offset as UARTRSR for reads +/// and UARTECR for writes, but really it's a single error status +/// register where writing anything to the register clears the error +/// bits. #[bitsize(32)] #[derive(Clone, Copy, DebugBits, FromBits)] pub struct ReceiveStatusErrorClear { @@ -196,54 +146,29 @@ impl Default for ReceiveStatusErrorClear { #[bitsize(32)] #[derive(Clone, Copy, DebugBits, FromBits)] /// Flag Register, `UARTFR` +/// +/// This has the usual inbound RS232 modem-control signals, plus flags +/// for RX and TX FIFO fill levels and a BUSY flag. #[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. + /// CTS: Clear to send 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. + /// DSR: Data set ready 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. + /// DCD: Data carrier detect 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. + /// BUSY: UART busy. In real hardware, set while the UART is + /// busy transmitting data. QEMU's implementation never sets BUSY. 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. + /// RXFE: Receive FIFO 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. + /// TXFF: Transmit FIFO 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. + /// RXFF: Receive FIFO 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. + /// TXFE: Transmit FIFO empty pub transmit_fifo_empty: bool, - /// `RI`, is `true` when `nUARTRI` is `LOW`. + /// RI: Ring indicator pub ring_indicator: bool, _reserved_zero_no_modify: u23, } @@ -270,54 +195,23 @@ impl Default for Flags { /// Line Control Register, `UARTLCR_H` #[doc(alias = "UARTLCR_H")] pub struct LineControl { - /// 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`. + /// BRK: Send break pub send_break: bool, - /// 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. + /// PEN: Parity enable pub parity_enabled: 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. + /// EPS: Even parity select pub parity: Parity, - /// 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. + /// STP2: Two stop bits select pub two_stops_bits: bool, - /// 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). + /// FEN: Enable FIFOs pub fifos_enabled: Mode, - /// WLEN Word length. These bits indicate the number of data bits - /// transmitted or received in a frame as follows: b11 = 8 bits + /// WLEN: Word length in bits + /// b11 = 8 bits /// b10 = 7 bits /// b01 = 6 bits /// b00 = 5 bits. pub word_length: WordLength, - /// 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. + /// SPS Stick parity select pub sticky_parity: bool, /// 31:8 - Reserved, do not modify, read as zero. _reserved_zero_no_modify: u24, @@ -342,11 +236,7 @@ impl Default for LineControl { /// `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, } @@ -381,88 +271,39 @@ pub enum WordLength { /// 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 +/// The `UARTCR` register is the control register. It contains various +/// enable bits, and the bits to write to set the usual outbound RS232 +/// modem control signals. All bits reset to 0 except TXE and RXE. #[bitsize(32)] #[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. + /// `UARTEN` UART enable: 0 = UART is disabled. 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. + /// `SIREN` `SIR` enable: disable or enable IrDA SIR ENDEC. + /// QEMU does not model this. 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. + /// `SIRLP` SIR low-power IrDA mode. QEMU does not model this. 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. + /// `LBE` Loopback enable: feed UART output back to the input 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. + /// `TXE` Transmit enable 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. + /// `RXE` Receive enable 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. + /// `DTR` Data transmit ready 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. + /// `RTS` Request to send 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). + /// `Out1` UART Out1 signal; can be used as 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). + /// `Out2` UART Out2 signal; can be used as 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. + /// `RTSEn` RTS hardware flow control enable 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. + /// `CTSEn` CTS hardware flow control enable pub cts_hardware_flow_control_enable: bool, /// 31:16 - Reserved, do not modify, read as zero. _reserved_zero_no_modify2: u16,