rigless 0.3.0

// Copyright (c) 2026 Rigless Labs.
// SPDX-License-Identifier: MIT OR Apache-2.0
//! The STM32F427: its peripheral models, one module per generated register layout, and the MCU that
//! is made of them.
//!
//! A model is a building block. It's written against one register layout and knows nothing of any
//! part or board, so a second part of the family carrying the same layout has it for free. The
//! serial interface here is `Spi`, once, and this part holds six of it.
//!
//! [`Stm32f427`] is the whole microcontroller, and it holds its models as **fields**: `mcu.rcc`,
//! `mcu.spi[0]`, `mcu.tim[0]`. Reaching one is a field access that can't fail. It runs on its own,
//! with no board: [`Stm32f427::new`] gives a part fresh out of reset, running on its internal
//! oscillator, with nothing on its pins.
//!
//! A board is that MCU plus what a board adds. Nothing here knows about a board.

pub mod adc;
pub mod dbg;
pub mod dma;
pub mod flash;
pub mod gpio;
pub mod i2c;
pub mod iwdg;
pub mod otg;
pub mod pwr;
pub mod rcc;
pub mod rtc;
pub mod sdio;
pub mod spi;
pub mod tim;
pub mod usart;

use std::num::NonZeroU32;

use crate::device::{DeviceContext, ErasedDevice, RegisterFile, ResetCause};
use crate::mcu::{Mcu, Operate};
use crate::snapshot::store;
use crate::soc::{Bus, Error, FieldSpec, Layout};
use crate::time::VirtualNanos;

use crate::cpu::armv7m::Dwt;
use adc::{Adc, AdcCommon};
use dbg::Dbg;
use dma::{Dma, Wire};
use flash::Flash;
use gpio::Gpio;
use i2c::I2c;
use iwdg::Iwdg;
use otg::Otg;
use pwr::Pwr;
use rcc::Rcc;
use rtc::Rtc;
use sdio::Sdio;
use spi::Spi;
use tim::{Advanced, Counter, General, Tim};
use usart::{Kind, Usart};

/// What every bus runs at until a firmware touches the clock tree: the 16 MHz HSI, since `RCC_CFGR`
/// resets to zero and both peripheral prescalers are one. RM0090 rev 22 sections 6.2.2 and 6.3.3.
/// From the first write to the tree the clock controller drives what each bus comes to, and
/// `memory_map.rs` says which output each model that keeps time runs on.
const RESET_BUS_HZ: u64 = rcc::HSI_HZ;

/// One whole STM32F427: the bus, and a model for every instance this part has one for.
///
/// The fields are the part's inventory. Everything else about it (where each answers, what its
/// registers reset to, the corrections against RM0090) is the bus, built by
/// [`memory_map::builder`](super::memory_map::builder).
///
/// A part with no crystals, no rail and nothing on its buses: those are a board's, and a board
/// attaches them to these fields after the part is built.
#[derive(Debug)]
pub struct Stm32f427 {
    /// Reset and clock control, RM0090 rev 22 chapter 6.
    pub rcc: Rcc,
    /// The power controller, sections 5.5.1 and 5.5.2.
    pub pwr: Pwr,
    /// The eleven ports of chapter 8, in the order of [`PORTS`]. One model answers for all of them,
    /// because they're one layout and their reset values are the instances'.
    pub gpio: [Gpio; PORTS.len()],
    /// The six serial interfaces of chapter 28, in the manual's order. The two extended blocks the
    /// same chapter gives another job aren't among them. See [`SERIAL_INTERFACES`].
    pub spi: [Spi; SERIAL_INTERFACES.len()],
    /// The eight serial ports of chapter 30, in the order of [`SERIAL_PORTS`]: two layouts and one model,
    /// each answering from the table its entry names.
    pub usart: [Usart; SERIAL_PORTS.len()],
    /// The three inter-integrated circuit interfaces of chapter 27, one layout and one model,
    /// controller mode only, in the order of [`I2C_INTERFACES`].
    pub i2c: [I2c; I2C_INTERFACES.len()],
    /// The embedded flash memory interface of chapter 3.
    pub flash: Flash,
    /// The three converters of chapter 13, in the order of [`CONVERTERS`].
    pub adc: [Adc; CONVERTERS.len()],
    /// The converters' common block, which clocks them.
    pub adc_common: AdcCommon,
    /// The four general-purpose timers of chapter 18, in the order of [`TIMERS`]. They're two
    /// layouts and one model, counting in the width their table entry gives. Where the wide pair's
    /// two tables differ is the option register, and `tim.rs` records it.
    pub tim: [Tim<General>; TIMERS.len()],
    /// The two advanced-control timers of chapter 17, in the order of [`ADVANCED_TIMERS`]: the same model
    /// as the four above with the chapter's repetition counter, break, dead-time and complementary outputs.
    pub advanced: [Tim<Advanced>; ADVANCED_TIMERS.len()],
    /// The two direct memory access controllers of chapter 10, in the order of [`CONTROLLERS`].
    /// They're one layout and one model. What differs between them is the part's, and it's in that
    /// table.
    pub dma: [Dma; CONTROLLERS.len()],
    /// The USB on-the-go full-speed core of chapter 34, as far as its reset register. One register
    /// of nineteen and a deliberate partial. `otg.rs` records what it leaves out.
    pub otg: Otg,
    /// The secure digital card interface of chapter 31. A board puts a card on it. A part with
    /// nothing in the slot is a part with an empty slot, which is what the firmware then sees.
    pub sdio: Sdio,
    /// The backup domain, as far as the reset that clears it.
    pub rtc: Rtc,
    /// The MCU debug component, RM0090 rev 22 section 38.16, on the core's own private peripheral
    /// bus rather than this part's.
    pub dbg: Dbg,
    /// The independent watchdog of chapter 21.
    pub iwdg: Iwdg,
    /// The cycle counter the processor brings with it, which is ARM's rather than ST's and so is
    /// described in neither manual on this part's shelf. `cpu::armv7m` says which two describe it.
    pub dwt: Dwt,
    bus: Bus,
    /// Which field answers for each slot of the bus, resolved once in [`Stm32f427::new`] so that
    /// nothing after it looks a peripheral up by name.
    wiring: Box<[Field]>,
    /// Where each field's register file lives, resolved once for the same reason.
    slots: Slots,
}

/// The slot each model's register file is in. A model keeps what the manual calls its state in the
/// register file and what it calls its wires in itself, so reaching one to drive it from outside
/// means reaching both. These indices are what pairs them without a name.
#[derive(Debug, Clone, Copy)]
struct Slots {
    rcc: usize,
    pwr: usize,
    gpio: [usize; PORTS.len()],
    spi: [usize; SERIAL_INTERFACES.len()],
    usart: [usize; SERIAL_PORTS.len()],
    i2c: [usize; I2C_INTERFACES.len()],
    flash: usize,
    adc: [usize; CONVERTERS.len()],
    adc_common: usize,
    tim: [usize; TIMERS.len()],
    advanced: [usize; ADVANCED_TIMERS.len()],
    dma: [usize; CONTROLLERS.len()],
    otg: usize,
    sdio: usize,
    rtc: usize,
    dbg: usize,
    iwdg: usize,
    dwt: usize,
}

/// Which of the MCU's fields answers for one slot of its bus.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum Field {
    /// A slot this part has no model for: its register file answers alone.
    None,
    Rcc,
    Pwr,
    /// The nth port, indexing [`Stm32f427::gpio`].
    Gpio(usize),
    /// The nth serial interface, indexing [`Stm32f427::spi`].
    Spi(usize),
    /// The nth serial port, indexing [`Stm32f427::usart`].
    Usart(usize),
    /// The nth inter-integrated circuit interface, indexing [`Stm32f427::i2c`].
    I2c(usize),
    /// The flash interface, [`Stm32f427::flash`].
    Flash,
    /// The nth converter, indexing [`Stm32f427::adc`].
    Adc(usize),
    AdcCommon,
    /// The nth timer, indexing [`Stm32f427::tim`].
    Tim(usize),
    /// The nth advanced-control timer, indexing [`Stm32f427::advanced`].
    Advanced(usize),
    /// The nth controller, indexing [`Stm32f427::dma`].
    Dma(usize),
    /// The USB core, [`Stm32f427::otg`].
    Otg,
    /// The card interface, [`Stm32f427::sdio`].
    Sdio,
    /// The backup domain, [`Stm32f427::rtc`].
    Rtc,
    /// The MCU debug component, [`Stm32f427::dbg`].
    Dbg,
    /// The independent watchdog, [`Stm32f427::iwdg`].
    Iwdg,
    /// The processor's cycle counter, [`Stm32f427::dwt`].
    Dwt,
}

impl Field {
    /// Every field this part has, which is what [`Stm32f427::new`] walks.
    ///
    /// Adding a field to the MCU means adding it here, and [`Field::instance`] below is an
    /// exhaustive match, so the compiler refuses a field that has no instance to answer for. That's
    /// the whole reason the mapping is written this way round: a table of names would let a field
    /// be forgotten and leave it pointing at whatever slot came first.
    fn all() -> Vec<Self> {
        let mut all = vec![Self::Rcc, Self::Pwr];
        all.extend((0..PORTS.len()).map(Self::Gpio));
        all.extend((0..SERIAL_INTERFACES.len()).map(Self::Spi));
        all.extend((0..SERIAL_PORTS.len()).map(Self::Usart));
        all.extend((0..I2C_INTERFACES.len()).map(Self::I2c));
        all.push(Self::Flash);
        all.extend((0..CONVERTERS.len()).map(Self::Adc));
        all.push(Self::AdcCommon);
        all.extend((0..TIMERS.len()).map(Self::Tim));
        all.extend((0..ADVANCED_TIMERS.len()).map(Self::Advanced));
        all.extend((0..CONTROLLERS.len()).map(Self::Dma));
        all.push(Self::Otg);
        all.push(Self::Sdio);
        all.push(Self::Rtc);
        all.push(Self::Dbg);
        all.push(Self::Iwdg);
        all.push(Self::Dwt);
        all
    }

    /// The instance this field answers for.
    fn instance(self) -> &'static str {
        match self {
            Self::None => unreachable!("the unmodeled slot answers for no instance"),
            Self::Rcc => "RCC",
            Self::Pwr => "PWR",
            Self::Gpio(nth) => PORTS[nth],
            Self::Spi(nth) => SERIAL_INTERFACES[nth],
            Self::Usart(nth) => SERIAL_PORTS[nth].instance,
            Self::I2c(nth) => I2C_INTERFACES[nth],
            Self::Flash => "FLASH",
            Self::Adc(nth) => CONVERTERS[nth],
            Self::AdcCommon => ADC_COMMON,
            Self::Tim(nth) => TIMERS[nth].instance,
            Self::Advanced(nth) => ADVANCED_TIMERS[nth].instance,
            Self::Dma(nth) => CONTROLLERS[nth].instance,
            // ST's file splits one peripheral into four blocks. This model answers for the first.
            Self::Otg => "OTG_FS_GLOBAL",
            Self::Sdio => "SDIO",
            Self::Rtc => "RTC",
            Self::Dbg => "DBG",
            Self::Iwdg => "IWDG",
            Self::Dwt => crate::cpu::armv7m::DWT,
        }
    }
}

/// The serial interfaces of chapter 28, in the manual's order, which is the order of
/// [`Stm32f427::spi`].
///
/// RM0090 rev 22 section 28.4.2: "The extended I2Ss (`I2Sx_ext`) can be used only in full duplex
/// mode. The `I2Sx_ext` operate always in slave mode." `I2S2ext` and `I2S3ext` carry this layout
/// and aren't serial interfaces, so they're not here and the part answers for neither.
pub const SERIAL_INTERFACES: [&str; 6] = ["SPI1", "SPI2", "SPI3", "SPI4", "SPI5", "SPI6"];

/// The three inter-integrated circuit interfaces of chapter 27, one layout, controller mode only,
/// `i2c.rs`, in the manual's order, which is the order of [`Stm32f427::i2c`].
pub const I2C_INTERFACES: [&str; 3] = ["I2C1", "I2C2", "I2C3"];

/// One serial port as the part carries it: the instance, and the table it answers from.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct SerialPort {
    /// The instance, as the vendor names it.
    pub instance: &'static str,
    /// Which of chapter 30's two tables it has, table 148.
    pub kind: Kind,
}

/// The three converters of chapter 13, in the manual's order, which is the order of [`Stm32f427::adc`].
pub const CONVERTERS: [&str; 3] = ["ADC1", "ADC2", "ADC3"];
/// The converters' common block, 13.13.15 to 13.13.17, as ST's file names it.
pub const ADC_COMMON: &str = "C_ADC";

/// The eight serial ports of chapter 30, which is the order of [`Stm32f427::usart`]: the six with every
/// register, then the two ST's file gives the shorter table.
pub const SERIAL_PORTS: [SerialPort; 8] = [
    SerialPort {
        instance: "USART1",
        kind: Kind::Usart,
    },
    SerialPort {
        instance: "USART2",
        kind: Kind::Usart,
    },
    SerialPort {
        instance: "USART3",
        kind: Kind::Usart,
    },
    SerialPort {
        instance: "USART6",
        kind: Kind::Usart,
    },
    SerialPort {
        instance: "UART7",
        kind: Kind::Usart,
    },
    SerialPort {
        instance: "UART8",
        kind: Kind::Usart,
    },
    SerialPort {
        instance: "UART4",
        kind: Kind::Uart,
    },
    SerialPort {
        instance: "UART5",
        kind: Kind::Uart,
    },
];

/// One timer of chapter 17 or 18 as the part wires it: how wide it counts, RM0090 rev 22 sections 17.2
/// and 18.2, which is the whole of what separates the four of chapter 18.
#[derive(Debug, Clone, Copy)]
pub struct Timer {
    /// The instance, as the vendor names it.
    pub instance: &'static str,
    /// What it counts in, 18.2.
    pub counter: Counter,
}

/// Every timer of chapter 18, in the manual's order, which is the order of [`Stm32f427::tim`].
///
/// ST's file gives each of the four a layout of its own, and the four are two: TIM2 and TIM5 carry
/// an option register the sixteen-bit pair doesn't have, and within each pair the tables are
/// identical. So the part points each timer at the layout of its pair, `memory_map.rs` chooses
/// which by the counter, and `tim.rs` records the one register that differs inside the wide pair.
/// Chapter 17's two are [`ADVANCED_TIMERS`], the same model through its `Advanced` family. Chapters 19
/// and 20's are a different shape, and the part has no model for them.
pub const TIMERS: [Timer; 4] = [
    Timer {
        instance: "TIM2",
        counter: Counter::Wide,
    },
    Timer {
        instance: "TIM3",
        counter: Counter::Narrow,
    },
    Timer {
        instance: "TIM4",
        counter: Counter::Narrow,
    },
    Timer {
        instance: "TIM5",
        counter: Counter::Wide,
    },
];

/// The two timers of chapter 17, in the manual's order, which is the order of [`Stm32f427::advanced`].
/// Both count in sixteen bits, 17.2, and both answer from the one layout ST's file gives them.
pub const ADVANCED_TIMERS: [Timer; 2] = [
    Timer {
        instance: "TIM1",
        counter: Counter::Narrow,
    },
    Timer {
        instance: "TIM8",
        counter: Counter::Narrow,
    },
];

/// One direct memory access controller as the part wires it: RM0090 rev 22 tables 43 and 44 for the
/// requests that reach it, and the note under figure 34 for whether its peripheral port is on the bus
/// matrix, which is what decides whether its streams can move memory to memory.
#[derive(Debug)]
pub struct Controller {
    /// The instance, as the vendor names it.
    pub instance: &'static str,
    /// Which peripheral request reaches which of its channels and streams.
    pub wiring: &'static [Wire],
    /// Which peripheral line is the last-data signal of section 10.3.15, and the streams it ends.
    pub last_data: &'static [Wire],
    /// Whether its peripheral port reaches the bus matrix.
    pub reaches_memory: bool,
}

/// The two controllers of chapter 10, in the order of [`Stm32f427::dma`].
///
/// The note under figure 34 is the whole of the difference between them: "The DMA1 controller AHB
/// peripheral port is not connected to the bus matrix like in the case of the DMA2 controller, thus only
/// DMA2 streams are able to perform memory-to-memory transfers."
pub static CONTROLLERS: [Controller; 2] = [
    Controller {
        instance: "DMA1",
        wiring: &DMA1_REQUESTS,
        last_data: &[],
        reaches_memory: false,
    },
    Controller {
        instance: "DMA2",
        wiring: &DMA2_REQUESTS,
        last_data: &DMA2_LAST_DATA,
        reaches_memory: true,
    },
];

/// RM0090 rev 22 section 10.3.15: the one peripheral "able to signal the end of the transfer" is the card
/// interface, and 31.3.2 step 4d has a firmware make it the flow controller of the stream it uses. The
/// signal arrives where its request does, on channel 4 of streams 3 and 6.
static DMA2_LAST_DATA: [Wire; 1] = [Wire {
    instance: "SDIO",
    request: sdio::LAST_DATA_REQUEST,
    channel: 4,
    streams: &[3, 6],
}];

/// RM0090 rev 22 table 43, for every request an instance this part models can drive.
///
/// A cell of that table names a peripheral request, and its row and column name the channel and the
/// stream the request reaches. This is the same statement the way a controller needs it. Only
/// instances that really drive a request are here, because a row for one that doesn't would name an
/// output no model has. Here that's the serial ports, the serial interfaces and the inter-integrated
/// circuit interfaces, and [`DMA2_REQUESTS`] adds the converters and the card interface. The timers
/// drive their request outputs too, and their rows are left out, so no stream serves a timer yet.
static DMA1_REQUESTS: [Wire; 23] = [
    Wire {
        instance: "I2C1",
        request: i2c::RECEIVE_REQUEST,
        channel: 1,
        streams: &[0, 5],
    },
    Wire {
        instance: "I2C1",
        request: i2c::TRANSMIT_REQUEST,
        channel: 1,
        streams: &[6, 7],
    },
    Wire {
        instance: "I2C3",
        request: i2c::RECEIVE_REQUEST,
        channel: 3,
        streams: &[2],
    },
    Wire {
        instance: "I2C3",
        request: i2c::TRANSMIT_REQUEST,
        channel: 3,
        streams: &[4],
    },
    Wire {
        instance: "I2C2",
        request: i2c::RECEIVE_REQUEST,
        channel: 7,
        streams: &[2, 3],
    },
    Wire {
        instance: "I2C2",
        request: i2c::TRANSMIT_REQUEST,
        channel: 7,
        streams: &[7],
    },
    Wire {
        instance: "UART5",
        request: usart::RECEIVE_REQUEST,
        channel: 4,
        streams: &[0],
    },
    Wire {
        instance: "USART3",
        request: usart::RECEIVE_REQUEST,
        channel: 4,
        streams: &[1],
    },
    Wire {
        instance: "UART4",
        request: usart::RECEIVE_REQUEST,
        channel: 4,
        streams: &[2],
    },
    Wire {
        instance: "USART3",
        request: usart::TRANSMIT_REQUEST,
        channel: 4,
        streams: &[3],
    },
    Wire {
        instance: "UART4",
        request: usart::TRANSMIT_REQUEST,
        channel: 4,
        streams: &[4],
    },
    Wire {
        instance: "USART2",
        request: usart::RECEIVE_REQUEST,
        channel: 4,
        streams: &[5],
    },
    Wire {
        instance: "USART2",
        request: usart::TRANSMIT_REQUEST,
        channel: 4,
        streams: &[6],
    },
    Wire {
        instance: "UART5",
        request: usart::TRANSMIT_REQUEST,
        channel: 4,
        streams: &[7],
    },
    Wire {
        instance: "UART8",
        request: usart::TRANSMIT_REQUEST,
        channel: 5,
        streams: &[0],
    },
    Wire {
        instance: "UART7",
        request: usart::TRANSMIT_REQUEST,
        channel: 5,
        streams: &[1],
    },
    Wire {
        instance: "UART7",
        request: usart::RECEIVE_REQUEST,
        channel: 5,
        streams: &[3],
    },
    Wire {
        instance: "UART8",
        request: usart::RECEIVE_REQUEST,
        channel: 5,
        streams: &[6],
    },
    Wire {
        instance: "USART3",
        request: usart::TRANSMIT_REQUEST,
        channel: 7,
        streams: &[4],
    },
    Wire {
        instance: "SPI3",
        request: spi::RECEIVE_REQUEST,
        channel: 0,
        streams: &[0, 2],
    },
    Wire {
        instance: "SPI3",
        request: spi::TRANSMIT_REQUEST,
        channel: 0,
        streams: &[5, 7],
    },
    Wire {
        instance: "SPI2",
        request: spi::RECEIVE_REQUEST,
        channel: 0,
        streams: &[3],
    },
    Wire {
        instance: "SPI2",
        request: spi::TRANSMIT_REQUEST,
        channel: 0,
        streams: &[4],
    },
];

/// RM0090 rev 22 table 44, read as [`DMA1_REQUESTS`] reads table 43.
static DMA2_REQUESTS: [Wire; 20] = [
    Wire {
        instance: "ADC1",
        request: adc::DMA_REQUEST,
        channel: 0,
        streams: &[0, 4],
    },
    Wire {
        instance: "ADC2",
        request: adc::DMA_REQUEST,
        channel: 1,
        streams: &[2, 3],
    },
    Wire {
        instance: "ADC3",
        request: adc::DMA_REQUEST,
        channel: 2,
        streams: &[0, 1],
    },
    Wire {
        instance: "USART1",
        request: usart::RECEIVE_REQUEST,
        channel: 4,
        streams: &[2, 5],
    },
    Wire {
        instance: "USART1",
        request: usart::TRANSMIT_REQUEST,
        channel: 4,
        streams: &[7],
    },
    Wire {
        instance: "USART6",
        request: usart::RECEIVE_REQUEST,
        channel: 5,
        streams: &[1, 2],
    },
    Wire {
        instance: "USART6",
        request: usart::TRANSMIT_REQUEST,
        channel: 5,
        streams: &[6, 7],
    },
    // Table 44 puts the card interface on channel 4, in the columns of streams 3 and 6. One line
    // for both directions, because one transfer runs at a time and `DTDIR` is what says which way
    // it goes.
    Wire {
        instance: "SDIO",
        request: sdio::TRANSFER_REQUEST,
        channel: 4,
        streams: &[3, 6],
    },
    Wire {
        instance: "SPI6",
        request: spi::TRANSMIT_REQUEST,
        channel: 1,
        streams: &[5],
    },
    Wire {
        instance: "SPI6",
        request: spi::RECEIVE_REQUEST,
        channel: 1,
        streams: &[6],
    },
    Wire {
        instance: "SPI5",
        request: spi::RECEIVE_REQUEST,
        channel: 2,
        streams: &[3],
    },
    Wire {
        instance: "SPI5",
        request: spi::TRANSMIT_REQUEST,
        channel: 2,
        streams: &[4],
    },
    Wire {
        instance: "SPI1",
        request: spi::RECEIVE_REQUEST,
        channel: 3,
        streams: &[0, 2],
    },
    Wire {
        instance: "SPI1",
        request: spi::TRANSMIT_REQUEST,
        channel: 3,
        streams: &[3, 5],
    },
    Wire {
        instance: "SPI4",
        request: spi::RECEIVE_REQUEST,
        channel: 4,
        streams: &[0],
    },
    Wire {
        instance: "SPI4",
        request: spi::TRANSMIT_REQUEST,
        channel: 4,
        streams: &[1],
    },
    Wire {
        instance: "SPI4",
        request: spi::RECEIVE_REQUEST,
        channel: 5,
        streams: &[3],
    },
    Wire {
        instance: "SPI4",
        request: spi::TRANSMIT_REQUEST,
        channel: 5,
        streams: &[4],
    },
    Wire {
        instance: "SPI5",
        request: spi::RECEIVE_REQUEST,
        channel: 7,
        streams: &[5],
    },
    Wire {
        instance: "SPI5",
        request: spi::TRANSMIT_REQUEST,
        channel: 7,
        streams: &[6],
    },
];

/// The ports of chapter 8, in the order their bases run, which is the order of [`Stm32f427::gpio`].
///
/// They're one layout. ST's file declares three, because RM0090 rev 22 sections 8.4.1, 8.4.3
/// and 8.4.4 give ports A and B reset values of their own, and a reset value belongs to the
/// instance rather than the layout. The part's memory map points every port at the one
/// table and states each one's reset values as corrections, so this model answers for all eleven.
pub const PORTS: [&str; 11] = [
    "GPIOA", "GPIOB", "GPIOC", "GPIOD", "GPIOE", "GPIOF", "GPIOG", "GPIOH", "GPIOI", "GPIOJ",
    "GPIOK",
];

/// Every field this part's models declare because the vendor's file omits it or splits it.
///
/// A generated table is ST's file transcribed and stays that way, so a field ST omits or splits is
/// declared by the model that needs it. A check that asks what the part declares has to
/// ask here as well as of the tables, and one that asks only the tables reads a hole where there's
/// none.
pub fn declared_fields() -> impl Iterator<Item = &'static FieldSpec> {
    [rcc::DECLARED, pwr::DECLARED, dbg::DECLARED, flash::DECLARED]
        .into_iter()
        .flatten()
        .copied()
}

store!(Stm32f427 {
    values: [
        rcc, pwr, gpio, flash, adc, adc_common, tim, advanced, otg, rtc, dbg, iwdg, dwt,
    ],
    parts: [spi, usart, i2c, dma, sdio, bus],
    built: [wiring, slots],
});

impl Stm32f427 {
    /// The part out of reset: every model fresh, running on the internal oscillator, nothing on its pins.
    ///
    /// Fails only if the part's own description is wrong: a field whose instance the tables don't
    /// carry, or a field wired to a slot whose layout it wasn't written for.
    pub fn new() -> Result<Self, Error> {
        let bus = super::memory_map::builder().build()?;
        let mut wiring = vec![Field::None; bus.slots().len()].into_boxed_slice();
        let mut slots = Slots {
            rcc: 0,
            pwr: 0,
            gpio: [0; PORTS.len()],
            spi: [0; SERIAL_INTERFACES.len()],
            usart: [0; SERIAL_PORTS.len()],
            i2c: [0; I2C_INTERFACES.len()],
            flash: 0,
            adc: [0; CONVERTERS.len()],
            adc_common: 0,
            tim: [0; TIMERS.len()],
            advanced: [0; ADVANCED_TIMERS.len()],
            dma: [0; CONTROLLERS.len()],
            otg: 0,
            sdio: 0,
            rtc: 0,
            dbg: 0,
            iwdg: 0,
            dwt: 0,
        };
        for field in Field::all() {
            let instance = field.instance();
            let slot = bus.slot(instance)?;
            wiring[slot] = field;
            match field {
                Field::Rcc => slots.rcc = slot,
                Field::Pwr => slots.pwr = slot,
                Field::Gpio(nth) => slots.gpio[nth] = slot,
                Field::Spi(nth) => slots.spi[nth] = slot,
                Field::Usart(nth) => slots.usart[nth] = slot,
                Field::I2c(nth) => slots.i2c[nth] = slot,
                Field::Flash => slots.flash = slot,
                Field::Adc(nth) => slots.adc[nth] = slot,
                Field::AdcCommon => slots.adc_common = slot,
                Field::Tim(nth) => slots.tim[nth] = slot,
                Field::Advanced(nth) => slots.advanced[nth] = slot,
                Field::Dma(nth) => slots.dma[nth] = slot,
                Field::Otg => slots.otg = slot,
                Field::Sdio => slots.sdio = slot,
                Field::Rtc => slots.rtc = slot,
                Field::Dbg => slots.dbg = slot,
                Field::Iwdg => slots.iwdg = slot,
                Field::Dwt => slots.dwt = slot,
                Field::None => unreachable!("Field::all names no unmodeled slot"),
            }
        }
        let adc_common = AdcCommon::with_clock(RESET_BUS_HZ);
        let mut mcu = Self {
            rcc: Rcc::new(),
            pwr: Pwr::new(),
            gpio: std::array::from_fn(|_| Gpio::default()),
            spi: std::array::from_fn(|_| Spi::with_clock(RESET_BUS_HZ)),
            usart: std::array::from_fn(|nth| {
                Usart::with_clock(SERIAL_PORTS[nth].kind, RESET_BUS_HZ)
            }),
            i2c: std::array::from_fn(|_| I2c::with_clock(RESET_BUS_HZ)),
            flash: Flash::with_clock(RESET_BUS_HZ),
            adc: std::array::from_fn(|_| Adc::with_clock(adc_common.driven_hz())),
            adc_common,
            tim: std::array::from_fn(|nth| Tim::with_clock(RESET_BUS_HZ, TIMERS[nth].counter)),
            advanced: std::array::from_fn(|nth| {
                Tim::with_clock(RESET_BUS_HZ, ADVANCED_TIMERS[nth].counter)
                    .breaks_on("RCC", rcc::CLOCK_FAILURE)
            }),
            dma: std::array::from_fn(|nth| {
                Dma::new(
                    CONTROLLERS[nth].wiring,
                    CONTROLLERS[nth].last_data,
                    CONTROLLERS[nth].reaches_memory,
                )
            }),
            otg: Otg,
            // The 48 MHz domain is the PLL's Q tap, section 6.3.2, and the PLL is off at reset.
            sdio: Sdio::with_clock(0),
            rtc: Rtc,
            dbg: Dbg,
            iwdg: Iwdg::new(),
            // The counter counts the core clock, which at reset is the same HSI the buses run on
            // because `RCC_CFGR.HPRE` resets to a divider of one, 6.3.3.
            dwt: Dwt::with_clock(RESET_BUS_HZ),
            bus,
            wiring,
            slots,
        };
        mcu.check()?;
        Ok(mcu)
    }
}

/// A model and the register file it keeps half its state in, paired by the slot resolved at
/// construction. Every accessor below is this with the field named, so the reaching is written once
/// whether the part has one of something or six. This is what a board drives a part through:
/// `mcu.power()` rather than a name and a downcast, and it can't fail.
fn with_registers<'a, M>(
    model: &'a mut M,
    bus: &'a mut Bus,
    slot: usize,
) -> (&'a mut M, &'a mut RegisterFile) {
    (model, bus.slot_mut(slot).registers_mut())
}

/// Drives an input of one at `at`, an input the bus doesn't carry: it gets its registers and a
/// context as on a bus access, so it may schedule and raise. This is the door a board's own parts
/// come through.
fn driving<M, T>(
    model: &mut M,
    bus: &mut Bus,
    slot: usize,
    at: VirtualNanos,
    input: impl FnOnce(&mut M, &mut RegisterFile, &mut DeviceContext<'_>) -> T,
) -> T {
    let (registers, mut context) = bus.drive(at, slot);
    input(model, registers, &mut context)
}

/// Copies `registers` of the instance at `slot` from `old` into `fresh`, for what a system reset
/// carries over rather than clearing: the calendar, `RCC_BDCR`, and the debug component's own three.
/// `old` and `fresh` share the same slot for one instance because `fresh` is always built by the same
/// deterministic bus as `old` was.
fn keep<L: Layout>(
    old: &Bus,
    fresh: &mut Bus,
    slot: usize,
    registers: impl IntoIterator<Item = L>,
) {
    for register in registers {
        let value = old.slots()[slot].registers().get(register);
        fresh.slot_mut(slot).registers_mut().set(register, value);
    }
}

impl Stm32f427 {
    /// The clock tree and the registers it keeps its state in.
    pub fn clocks(&mut self) -> (&mut Rcc, &mut RegisterFile) {
        let Self {
            rcc, bus, slots, ..
        } = self;
        with_registers(rcc, bus, slots.rcc)
    }

    /// Drives an input of the clock tree at `at`, an input the bus doesn't carry.
    pub fn drive_clocks<T>(
        &mut self,
        at: VirtualNanos,
        input: impl FnOnce(&mut Rcc, &mut RegisterFile, &mut DeviceContext<'_>) -> T,
    ) -> T {
        let Self {
            rcc, bus, slots, ..
        } = self;
        driving(rcc, bus, slots.rcc, at, input)
    }

    /// The regulator and the registers it keeps its state in.
    pub fn power(&mut self) -> (&mut Pwr, &mut RegisterFile) {
        let Self {
            pwr, bus, slots, ..
        } = self;
        with_registers(pwr, bus, slots.pwr)
    }

    /// The board's supply rail, in millivolts, fed to every instance that reads it: the regulator's
    /// own brownout detector, RM0090 rev 22 section 5.5.2, and the flash interface's `LATENCY` check
    /// against table 12, section 3.5.1. One board input, one setter, rather than a board or a reset
    /// calling `Pwr::set_supply` and `Flash::set_supply` apart and one of the two going unset.
    pub fn set_supply(&mut self, millivolts: u32) {
        let (power, registers) = self.power();
        power.set_supply(millivolts, registers);
        if let Some(millivolts) = NonZeroU32::new(millivolts) {
            self.flash.set_supply(millivolts);
        }
    }

    /// Drives an input of the regulator at `at`, an input the bus doesn't carry.
    pub fn drive_power<T>(
        &mut self,
        at: VirtualNanos,
        input: impl FnOnce(&mut Pwr, &mut RegisterFile, &mut DeviceContext<'_>) -> T,
    ) -> T {
        let Self {
            pwr, bus, slots, ..
        } = self;
        driving(pwr, bus, slots.pwr, at, input)
    }
    /// The nth port of [`PORTS`], with the registers it keeps its state in.
    pub fn port(&mut self, nth: usize) -> (&mut Gpio, &mut RegisterFile) {
        let Self {
            gpio, bus, slots, ..
        } = self;
        with_registers(&mut gpio[nth], bus, slots.gpio[nth])
    }

    /// Drives an input of the nth port at `at`, an input the bus doesn't carry.
    pub fn drive_port<T>(
        &mut self,
        at: VirtualNanos,
        nth: usize,
        input: impl FnOnce(&mut Gpio, &mut RegisterFile, &mut DeviceContext<'_>) -> T,
    ) -> T {
        let Self {
            gpio, bus, slots, ..
        } = self;
        driving(&mut gpio[nth], bus, slots.gpio[nth], at, input)
    }

    /// The nth serial interface of [`SERIAL_INTERFACES`], with the registers it keeps its state in.
    pub fn serial(&mut self, nth: usize) -> (&mut Spi, &mut RegisterFile) {
        let Self {
            spi, bus, slots, ..
        } = self;
        with_registers(&mut spi[nth], bus, slots.spi[nth])
    }

    /// Drives an input of the nth serial interface at `at`, an input the bus doesn't carry.
    pub fn drive_serial<T>(
        &mut self,
        at: VirtualNanos,
        nth: usize,
        input: impl FnOnce(&mut Spi, &mut RegisterFile, &mut DeviceContext<'_>) -> T,
    ) -> T {
        let Self {
            spi, bus, slots, ..
        } = self;
        driving(&mut spi[nth], bus, slots.spi[nth], at, input)
    }

    /// The nth serial port of [`SERIAL_PORTS`], with the registers it keeps its state in.
    pub fn serial_port(&mut self, nth: usize) -> (&mut Usart, &mut RegisterFile) {
        let Self {
            usart, bus, slots, ..
        } = self;
        with_registers(&mut usart[nth], bus, slots.usart[nth])
    }

    /// Drives an input of the nth serial port at `at`, an input the bus doesn't carry.
    pub fn drive_serial_port<T>(
        &mut self,
        at: VirtualNanos,
        nth: usize,
        input: impl FnOnce(&mut Usart, &mut RegisterFile, &mut DeviceContext<'_>) -> T,
    ) -> T {
        let Self {
            usart, bus, slots, ..
        } = self;
        driving(&mut usart[nth], bus, slots.usart[nth], at, input)
    }

    /// The nth converter of [`CONVERTERS`], with the registers it keeps its state in.
    pub fn converter(&mut self, nth: usize) -> (&mut Adc, &mut RegisterFile) {
        let Self {
            adc, bus, slots, ..
        } = self;
        with_registers(&mut adc[nth], bus, slots.adc[nth])
    }

    /// The nth timer of [`TIMERS`], with the registers it keeps its state in.
    pub fn timer(&mut self, nth: usize) -> (&mut Tim<General>, &mut RegisterFile) {
        let Self {
            tim, bus, slots, ..
        } = self;
        with_registers(&mut tim[nth], bus, slots.tim[nth])
    }

    /// Drives an input of the nth timer at `at`, an input the bus doesn't carry.
    pub fn drive_timer<T>(
        &mut self,
        at: VirtualNanos,
        nth: usize,
        input: impl FnOnce(&mut Tim<General>, &mut RegisterFile, &mut DeviceContext<'_>) -> T,
    ) -> T {
        let Self {
            tim, bus, slots, ..
        } = self;
        driving(&mut tim[nth], bus, slots.tim[nth], at, input)
    }

    /// The nth advanced-control timer of [`ADVANCED_TIMERS`], with the registers it keeps its state in.
    pub fn advanced_timer(&mut self, nth: usize) -> (&mut Tim<Advanced>, &mut RegisterFile) {
        let Self {
            advanced,
            bus,
            slots,
            ..
        } = self;
        with_registers(&mut advanced[nth], bus, slots.advanced[nth])
    }

    /// Drives an input of the nth advanced-control timer at `at`, an input the bus doesn't carry.
    pub fn drive_advanced_timer<T>(
        &mut self,
        at: VirtualNanos,
        nth: usize,
        input: impl FnOnce(&mut Tim<Advanced>, &mut RegisterFile, &mut DeviceContext<'_>) -> T,
    ) -> T {
        let Self {
            advanced,
            bus,
            slots,
            ..
        } = self;
        driving(&mut advanced[nth], bus, slots.advanced[nth], at, input)
    }

    /// The nth controller of [`CONTROLLERS`], with the registers it keeps its state in.
    pub fn controller(&mut self, nth: usize) -> (&mut Dma, &mut RegisterFile) {
        let Self {
            dma, bus, slots, ..
        } = self;
        with_registers(&mut dma[nth], bus, slots.dma[nth])
    }

    /// Drives an input of the nth controller at `at`, an input the bus doesn't carry.
    pub fn drive_controller<T>(
        &mut self,
        at: VirtualNanos,
        nth: usize,
        input: impl FnOnce(&mut Dma, &mut RegisterFile, &mut DeviceContext<'_>) -> T,
    ) -> T {
        let Self {
            dma, bus, slots, ..
        } = self;
        driving(&mut dma[nth], bus, slots.dma[nth], at, input)
    }

    /// The USB core and the registers it keeps its state in.
    ///
    /// There's no `drive_` beside this one: the core has no input the bus doesn't carry until a
    /// host is on the far end of it.
    pub fn usb(&mut self) -> (&mut Otg, &mut RegisterFile) {
        let Self {
            otg, bus, slots, ..
        } = self;
        with_registers(otg, bus, slots.otg)
    }

    /// The card interface and the registers it keeps its state in.
    pub fn cards(&mut self) -> (&mut Sdio, &mut RegisterFile) {
        let Self {
            sdio, bus, slots, ..
        } = self;
        with_registers(sdio, bus, slots.sdio)
    }

    /// The flash interface and the registers it keeps its state in.
    pub fn program(&mut self) -> (&mut Flash, &mut RegisterFile) {
        let Self {
            flash, bus, slots, ..
        } = self;
        with_registers(flash, bus, slots.flash)
    }
}

impl Stm32f427 {
    /// Tells every chip a controller carried through a reset at `at` that its part restarted, with
    /// that controller's timeline, since the events it scheduled went with the old bus.
    fn chips_restarted(&mut self, at: VirtualNanos) {
        let Self {
            spi,
            usart,
            i2c,
            sdio,
            bus,
            slots,
            ..
        } = self;
        for (spi, &slot) in spi.iter_mut().zip(&slots.spi) {
            driving(spi, bus, slot, at, |spi, _, context| {
                spi.chips_restarted(context);
            });
        }
        for (usart, &slot) in usart.iter_mut().zip(&slots.usart) {
            driving(usart, bus, slot, at, |usart, _, context| {
                usart.chips_restarted(context);
            });
        }
        for (i2c, &slot) in i2c.iter_mut().zip(&slots.i2c) {
            driving(i2c, bus, slot, at, |i2c, _, context| {
                i2c.chips_restarted(context);
            });
        }
        driving(sdio, bus, slots.sdio, at, |sdio, _, context| {
            sdio.chips_restarted(context);
        });
    }
}

impl Mcu for Stm32f427 {
    fn bus(&self) -> &Bus {
        &self.bus
    }

    /// A system reset, RM0090 rev 22 section 6.1.1: a fresh part with what the board put on its
    /// pins still there, the reset flags carrying `cause`'s own flag beside the ones before, and
    /// the backup domain as it was. Section 6.1.3 keeps that domain through every reset but its
    /// own: the calendar, the twenty backup registers, the clock controller's `BDCR` and the backup
    /// regulator's enable. Sections 38.16.3 to 38.16.5 keep the debug component's three read-write
    /// registers through the same reset: a debugger's configuration of the part is a power-on
    /// reset's to clear, not this one's. The flash interface keeps its option bytes as the last
    /// commit left them, and the clock controller the LSI's calibrated rate. Regions and windows a
    /// board added to the bus stay.
    fn reset(&mut self, at: VirtualNanos, cause: ResetCause) {
        let mut fresh = Self::new().expect("a part that assembled once assembles again");
        let flags = self.bus.slots()[self.slots.rcc]
            .registers()
            .get(super::generated::rcc::Register::Csr);
        let (clocks, registers) = fresh.clocks();
        clocks.restarted(cause, flags, registers);
        let regulator = self.bus.slots()[self.slots.pwr]
            .registers()
            .get(super::generated::pwr::Register::Csr);
        let (power, registers) = fresh.power();
        power.keep_backup_regulator(regulator, registers);
        let (hse_hz, lse_hz) = self.rcc.crystals();
        fresh.rcc.attach_crystals(hse_hz, lse_hz);
        fresh.rcc.calibrate_lsi(self.rcc.lsi_hz());
        fresh.set_supply(self.pwr.supply());
        for (fresh, old) in fresh.spi.iter_mut().zip(&mut self.spi) {
            fresh.inherit(old);
        }
        for (fresh, old) in fresh.usart.iter_mut().zip(&mut self.usart) {
            fresh.inherit(old);
        }
        for (fresh, old) in fresh.i2c.iter_mut().zip(&mut self.i2c) {
            fresh.inherit(old);
        }
        for (fresh, old) in fresh.adc.iter_mut().zip(&self.adc) {
            fresh.inherit(old);
        }
        fresh.sdio.inherit(&mut self.sdio);
        let (optcr, optcr1) = self.flash.committed_options();
        let (flash, registers) = fresh.program();
        flash.keep_options(optcr, optcr1, registers);
        keep(
            &self.bus,
            &mut fresh.bus,
            self.slots.rtc,
            super::generated::rtc::Register::ALL,
        );
        keep(
            &self.bus,
            &mut fresh.bus,
            self.slots.rcc,
            [super::generated::rcc::Register::Bdcr],
        );
        keep(
            &self.bus,
            &mut fresh.bus,
            self.slots.dbg,
            [
                super::generated::dbg::Register::DbgmcuCr,
                super::generated::dbg::Register::DbgmcuApb1Fz,
                super::generated::dbg::Register::DbgmcuApb2Fz,
            ],
        );
        fresh
            .bus
            .keep_added(&self.bus)
            .expect("a part rebuilt from its own description");
        *self = fresh;
        self.chips_restarted(at);
    }

    /// [`Mcu::poll`] for the USARTs alone, the only models here with anything outside: a host on
    /// the wire, or a chip with words to send. Every other model's poll does nothing, and a stop
    /// comes often enough that asking each of them costs.
    // ceiling: a model of this part that looks outside must be listed here; upgrade when one
    // besides the USART does.
    fn poll(&mut self, now: VirtualNanos) {
        for slot in 0..self.wiring.len() {
            let Field::Usart(nth) = self.wiring[slot] else {
                continue;
            };
            let (carried, mut context) = self.bus.call(now, slot);
            self.usart[nth].poll(carried.registers_mut(), &mut context);
        }
    }

    fn split(&mut self, slot: usize) -> (&mut Bus, Option<&mut dyn ErasedDevice>) {
        let Self {
            rcc,
            pwr,
            gpio,
            spi,
            usart,
            i2c,
            flash,
            adc,
            adc_common,
            tim,
            advanced,
            dma,
            otg,
            sdio,
            rtc,
            dbg,
            iwdg,
            dwt,
            bus,
            wiring,
            ..
        } = self;
        // A window a board added has a slot past the part's own, and the board's model for it.
        let field = wiring.get(slot).copied().unwrap_or(Field::None);
        let model: Option<&mut dyn ErasedDevice> = match field {
            Field::None => None,
            Field::Rcc => Some(rcc),
            Field::Pwr => Some(pwr),
            Field::Gpio(nth) => Some(&mut gpio[nth]),
            Field::Spi(nth) => Some(&mut spi[nth]),
            Field::Usart(nth) => Some(&mut usart[nth]),
            Field::I2c(nth) => Some(&mut i2c[nth]),
            Field::Flash => Some(flash),
            Field::Adc(nth) => Some(&mut adc[nth]),
            Field::AdcCommon => Some(adc_common),
            Field::Tim(nth) => Some(&mut tim[nth]),
            Field::Advanced(nth) => Some(&mut advanced[nth]),
            Field::Dma(nth) => Some(&mut dma[nth]),
            Field::Otg => Some(otg),
            Field::Sdio => Some(sdio),
            Field::Rtc => Some(rtc),
            Field::Dbg => Some(dbg),
            Field::Iwdg => Some(iwdg),
            Field::Dwt => Some(dwt),
        };
        (bus, model)
    }

    fn bus_mut(&mut self) -> &mut Bus {
        &mut self.bus
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::collections::BTreeMap;

    use crate::soc::{Fault, Peripheral, RegisterSpec};

    /// Every instance of `layout` the part carries.
    fn instances_of(layout: &'static [RegisterSpec]) -> impl Iterator<Item = &'static Peripheral> {
        super::super::generated::PERIPHERALS
            .iter()
            .filter(move |peripheral| std::ptr::eq(peripheral.registers, layout))
    }

    /// Memory a board fits on the external memory interface's first SDRAM bank, RM0090 rev 22
    /// section 37.4 and figure 457.
    const BOARD_SDRAM: crate::soc::Region = crate::soc::Region::ram("sdram", 0xC000_0000, 16 << 20);

    /// A part with a board's worth on its pins and inside its backup domain, a timer running and a clock
    /// enabled: what a reset has to sort into kept and gone.
    fn a_part_with_a_board_on_it() -> Stm32f427 {
        use crate::chip::{memory_card, sd, uart};
        use crate::soc::stm32f427::generated::dbg::{
            Register as DbgRegister, dbgmcu_apb1_fz, dbgmcu_apb2_fz, dbgmcu_cr,
        };
        use crate::soc::stm32f427::generated::pwr::{
            Register as PwrRegister, cr as pwr_cr, csr as pwr_csr,
        };
        use crate::soc::stm32f427::generated::rcc::{
            Register as RccRegister, apb1enr, apb2enr, bdcr,
        };
        use crate::soc::stm32f427::generated::rtc::Register as RtcRegister;
        use crate::soc::stm32f427::generated::tim2::{Register as TimRegister, cr1};
        use crate::soc::stm32f427::generated::{DBG, RCC, TIM2};
        use crate::soc::{Layout, Width};

        let mut mcu = Stm32f427::new().expect("the part assembles");
        mcu.rcc.attach_crystals(24_000_000, 32_768);
        mcu.rcc.calibrate_lsi(29_000);
        mcu.set_supply(3300);
        mcu.spi[0].attach(crate::chip::spi::Pattern::default());
        mcu.usart[1].attach(uart::Pattern::default());
        mcu.usart[6].attach(uart::TcpPeer::listen(0).expect("a port is free"));
        mcu.sdio
            .attach(memory_card::MemoryCard::holding(&[0; sd::BLOCK]));
        mcu.adc[0].set_reference(3300);
        mcu.adc[0].set_input(adc::Channel::new(2).expect("a pin channel"), 1650);
        mcu.bus_mut()
            .add_region(BOARD_SDRAM)
            .expect("the first SDRAM bank is free");
        mcu.bus_mut()
            .add_window(super::super::NOR_PSRAM[3])
            .expect("NE4 is free");
        let at = VirtualNanos(0);
        let register = |base: u64, offset: u32| base + u64::from(offset);
        let enables = register(RCC.base, RccRegister::Apb2enr.spec().offset);
        mcu.write(at, enables, Width::W32, apb2enr::ADC1EN.mask())
            .expect("the enable takes the write");
        let (rtc, rcc, pwr) = (mcu.slots.rtc, mcu.slots.rcc, mcu.slots.pwr);
        mcu.bus_mut()
            .slot_mut(pwr)
            .registers_mut()
            .set(PwrRegister::Cr, pwr_cr::DBP.mask());
        mcu.bus_mut()
            .slot_mut(pwr)
            .registers_mut()
            .set(PwrRegister::Csr, pwr_csr::BRE.mask() | pwr_csr::BRR.mask());
        mcu.bus_mut()
            .slot_mut(rtc)
            .registers_mut()
            .set(RtcRegister::Bkp19r, 0x5EB0_0755);
        mcu.bus_mut()
            .slot_mut(rcc)
            .registers_mut()
            .set(RccRegister::Bdcr, bdcr::RTCEN.mask() | bdcr::LSEON.mask());
        mcu.write(
            at,
            register(RCC.base, RccRegister::Apb1enr.spec().offset),
            Width::W32,
            apb1enr::TIM2EN.mask(),
        )
        .expect("the enable takes the write");
        mcu.write(
            at,
            register(TIM2.base, TimRegister::Cr1.spec().offset),
            Width::W32,
            cr1::CEN.mask(),
        )
        .expect("the timer takes the write");
        assert!(
            mcu.next_event().is_some(),
            "the running timer scheduled its update"
        );
        // 38.16.3, 38.16.4, 38.16.5: a debugger's configuration, which a system reset must not undo.
        mcu.write(
            at,
            register(DBG.base, DbgRegister::DbgmcuCr.spec().offset),
            Width::W32,
            dbgmcu_cr::DBG_STOP.mask(),
        )
        .expect("the debug component takes the write");
        mcu.write(
            at,
            register(DBG.base, DbgRegister::DbgmcuApb1Fz.spec().offset),
            Width::W32,
            dbgmcu_apb1_fz::DBG_TIM5_STOP.mask(),
        )
        .expect("the debug component takes the write");
        mcu.write(
            at,
            register(DBG.base, DbgRegister::DbgmcuApb2Fz.spec().offset),
            Width::W32,
            dbgmcu_apb2_fz::DBG_TIM1_STOP.mask(),
        )
        .expect("the debug component takes the write");
        mcu
    }

    /// A reset from the pin, section 6.1.1's external reset, leaves `PADRSTF` beside the flags the part
    /// had and not the software's, and the core's own request then adds `SFTRSTF`.
    #[test]
    fn a_reset_from_the_pin_leaves_its_own_flag_and_not_the_softwares() {
        use crate::soc::stm32f427::generated::RCC;
        use crate::soc::stm32f427::generated::rcc::{Register as RccRegister, csr};
        use crate::soc::{Layout, Width};

        let at = VirtualNanos(0);
        let flags = RCC.base + u64::from(RccRegister::Csr.spec().offset);
        let mut mcu = a_part_with_a_board_on_it();
        mcu.write(at, flags, Width::W32, csr::RMVF.mask())
            .expect("the flags take the write");
        mcu.reset(at, ResetCause::Pin);
        let value = mcu.read(at, flags, Width::W32).expect("the flags answer");
        assert!(csr::PADRSTF.is_set(value));
        assert!(!csr::SFTRSTF.is_set(value) && !csr::WDGRSTF.is_set(value));
        mcu.reset(at, ResetCause::Core);
        let value = mcu.read(at, flags, Width::W32).expect("the flags answer");
        assert!(csr::PADRSTF.is_set(value) && csr::SFTRSTF.is_set(value));
    }

    /// A system reset rebuilds the part and keeps what the board put on its pins and what the
    /// backup domain holds: the chips on the buses, the card, the crystals, the rail, the
    /// converter's inputs, the calendar's registers, `BDCR` and the backup regulator's enable, and
    /// what a debugger left in the debug component's freeze registers. The flash interface keeps its
    /// option bytes as the last commit left them, and the clock controller the LSI's calibrated rate.
    /// The reset flags say why the part restarted. Every other register is back at its reset value
    /// and nothing is scheduled.
    #[test]
    fn a_reset_keeps_the_pins_and_the_backup_domain_and_nothing_else() {
        use crate::soc::stm32f427::generated::adc1::{Register as AdcRegister, cr2, sqr3, sr};
        use crate::soc::stm32f427::generated::dbg::{
            Register as DbgRegister, dbgmcu_apb1_fz, dbgmcu_apb2_fz, dbgmcu_cr,
        };
        use crate::soc::stm32f427::generated::pwr::{Register as PwrRegister, csr as pwr_csr};
        use crate::soc::stm32f427::generated::rcc::{Register as RccRegister, apb2enr, bdcr, csr};
        use crate::soc::stm32f427::generated::rtc::Register as RtcRegister;
        use crate::soc::stm32f427::generated::{ADC1, DBG, RCC, RTC};
        use crate::soc::{Layout, Width};

        let at = VirtualNanos(0);
        let register = |base: u64, offset: u32| base + u64::from(offset);
        let enables = register(RCC.base, RccRegister::Apb2enr.spec().offset);
        let mut mcu = a_part_with_a_board_on_it();
        mcu.reset(at, ResetCause::Core);
        assert_eq!(
            mcu.read(at, enables, Width::W32)
                .expect("the enables answer"),
            0,
            "every register is at its reset value"
        );
        assert_eq!(mcu.next_event(), None);
        assert_eq!(mcu.rcc.crystals(), (24_000_000, 32_768));
        assert_eq!(mcu.bus().memory().last(), Some(&BOARD_SDRAM));
        let ne4 = super::super::NOR_PSRAM[3].base;
        assert!(
            matches!(
                mcu.read(at, ne4, Width::W16),
                Err(Fault::Gated {
                    instance: "NE4",
                    ..
                })
            ),
            "the board's window is still there, behind its gate"
        );
        assert_eq!(
            mcu.rcc.lsi_hz(),
            29_000,
            "a board's LSI calibration is the board's, not a register's"
        );
        assert_eq!(mcu.pwr.supply(), 3300);
        assert!(mcu.spi[0].attached() && mcu.usart[1].attached() && mcu.usart[6].attached());
        assert!(!mcu.spi[1].attached());
        assert!(mcu.sdio.attached());
        // Half the rail on channel 2 converts to 2047 after fifteen cycles at the reset 8 MHz, 13.5.
        mcu.write(at, enables, Width::W32, apb2enr::ADC1EN.mask())
            .expect("the enable takes the write");
        let adc = |register: AdcRegister| ADC1.base + u64::from(register.spec().offset);
        mcu.write(at, adc(AdcRegister::Sqr3), Width::W32, sqr3::SQ1.set(0, 2))
            .expect("the converter takes the write");
        mcu.write(at, adc(AdcRegister::Cr2), Width::W32, cr2::ADON.mask())
            .expect("the converter takes the write");
        mcu.write(
            at,
            adc(AdcRegister::Cr2),
            Width::W32,
            cr2::ADON.mask() | cr2::SWSTART.mask(),
        )
        .expect("the converter takes the write");
        let converted = VirtualNanos(1_875);
        mcu.advance_to(converted);
        assert!(
            sr::EOC.is_set(
                mcu.read(converted, adc(AdcRegister::Sr), Width::W32)
                    .expect("the converter answers")
            )
        );
        assert_eq!(
            mcu.read(converted, adc(AdcRegister::Dr), Width::W32)
                .expect("the converter answers"),
            2047,
            "the pin's voltage is still there"
        );
        let backup = register(RTC.base, RtcRegister::Bkp19r.spec().offset);
        assert_eq!(
            mcu.read(at, backup, Width::W32)
                .expect("the backup domain answers"),
            0x5EB0_0755
        );
        let domain = mcu
            .registers("RCC")
            .expect("an instance")
            .get(RccRegister::Bdcr);
        assert!(bdcr::RTCEN.is_set(domain) && bdcr::LSEON.is_set(domain));
        let flags = mcu
            .registers("RCC")
            .expect("an instance")
            .get(RccRegister::Csr);
        assert!(
            csr::SFTRSTF.is_set(flags) && csr::PADRSTF.is_set(flags) && csr::PORRSTF.is_set(flags),
            "the software reset's flag joins the power-on ones the part started with: {flags:#x}"
        );
        let regulator = mcu
            .registers("PWR")
            .expect("an instance")
            .get(PwrRegister::Csr);
        assert!(
            pwr_csr::BRE.is_set(regulator) && pwr_csr::BRR.is_set(regulator),
            "the backup regulator is still on: {regulator:#x}"
        );
        let debug_read = |mcu: &mut Stm32f427, offset: u32| {
            mcu.read(at, register(DBG.base, offset), Width::W32)
                .expect("the debug component answers")
        };
        assert!(
            dbgmcu_cr::DBG_STOP.is_set(debug_read(&mut mcu, DbgRegister::DbgmcuCr.spec().offset)),
            "38.16.3: a system reset does not touch the debug component"
        );
        assert!(
            dbgmcu_apb1_fz::DBG_TIM5_STOP.is_set(debug_read(
                &mut mcu,
                DbgRegister::DbgmcuApb1Fz.spec().offset
            )),
            "38.16.4: a system reset does not touch the debug component"
        );
        assert!(
            dbgmcu_apb2_fz::DBG_TIM1_STOP.is_set(debug_read(
                &mut mcu,
                DbgRegister::DbgmcuApb2Fz.spec().offset
            )),
            "38.16.5: a system reset does not touch the debug component"
        );
    }

    /// A bank of the external memory interface answers only once `FMC_BCRx.MBKEN` enables it,
    /// section 37.3, and then reaches whatever the board put there, which here is nothing.
    #[test]
    fn a_nor_psram_bank_answers_only_once_its_control_register_enables_it() {
        use crate::soc::stm32f427::generated::FMC;
        use crate::soc::stm32f427::generated::fmc::{Register as FmcRegister, bcr1};
        use crate::soc::{Gate, Layout, Width};

        let at = VirtualNanos(0);
        let mut mcu = Stm32f427::new().expect("the part assembles");
        for bank in super::super::NOR_PSRAM {
            mcu.bus_mut().add_window(bank).expect("the banks are free");
        }
        let ne3 = super::super::NOR_PSRAM[2].base;
        assert_eq!(
            mcu.read(at, ne3, Width::W16),
            Err(Fault::Gated {
                instance: "NE3",
                register: "window",
                by: Gate::by("FMC", "BCR3", "MBKEN"),
            })
        );
        let bcr3 = FMC.base + u64::from(FmcRegister::Bcr3.spec().offset);
        mcu.write(at, bcr3, Width::W32, bcr1::MBKEN.mask())
            .expect("the control register answers");
        assert_eq!(
            mcu.read(at, ne3, Width::W16),
            Err(Fault::Unmapped { address: ne3 })
        );
    }

    /// Every model that keeps time runs on an output of the tree, and nothing else does: the description
    /// is where the wiring is written, and a model built with a rate and never wired keeps it forever.
    #[test]
    fn every_model_that_keeps_time_runs_on_a_clock_the_tree_drives() {
        let mcu = Stm32f427::new().unwrap();
        for field in Field::all() {
            let keeps_time = matches!(
                field,
                Field::Spi(_)
                    | Field::Usart(_)
                    | Field::I2c(_)
                    | Field::Flash
                    | Field::Adc(_)
                    | Field::AdcCommon
                    | Field::Tim(_)
                    | Field::Advanced(_)
                    | Field::Sdio
                    | Field::Iwdg
                    | Field::Dwt
            );
            let clock = mcu.bus().clock_of(field.instance());
            assert_eq!(clock.is_some(), keeps_time, "{}", field.instance());
            // A converter runs on its common block's output, 13.3.2, and the block on the tree.
            let driver = if matches!(field, Field::Adc(_)) {
                ADC_COMMON
            } else {
                "RCC"
            };
            if let Some(clock) = clock {
                assert_eq!(clock.instance, driver, "{}", field.instance());
            }
        }
    }

    /// Every field a model declares is in the `DECLARED` beside it.
    ///
    /// The lists are written by hand and nothing else needs them complete, so a field left out of one is
    /// silent: it reads as a hole in ST's file wherever anything asks the part what it declares. The
    /// module's own source is the second witness, read the way `tests/conformance.rs` reads the
    /// firmware's, because the declaration and the list that carries it are two statements of one fact.
    #[test]
    fn every_field_a_model_declares_is_in_the_list_beside_it() {
        const SOURCES: [(&str, &str, &[&FieldSpec]); 3] = [
            ("rcc", include_str!("peripherals/rcc.rs"), rcc::DECLARED),
            ("pwr", include_str!("peripherals/pwr.rs"), pwr::DECLARED),
            ("dbg", include_str!("peripherals/dbg.rs"), dbg::DECLARED),
        ];

        for (model, source, declared) in SOURCES {
            let written: Vec<&str> = source
                .lines()
                .filter_map(|line| line.trim().strip_prefix("pub static "))
                .filter_map(|rest| rest.split_once(": FieldSpec"))
                .map(|(name, _)| name)
                .collect();
            assert!(
                !written.is_empty(),
                "{model} declares none, so this reads nothing"
            );
            let listed: Vec<&str> = declared.iter().map(|field| field.name).collect();
            let forgotten: Vec<&&str> = written
                .iter()
                .filter(|name| !listed.contains(*name))
                .collect();
            assert!(
                forgotten.is_empty(),
                "{model} declares {forgotten:?} and leaves them out of its DECLARED"
            );
        }
    }

    /// Every test a model's coverage table names is a test that exists.
    ///
    /// The last column of the table at the top of each model is the whole claim that a behavior is
    /// proved, and each name in it is written by hand against a function in another file. Renaming that
    /// function, or dropping it, leaves the table asserting something nobody runs. This is the two files
    /// held against each other, the same shape as the check above.
    ///
    /// Only the four-column tables are read: the three-column one beside them says what a model leaves
    /// out, and it names sections rather than tests.
    #[test]
    fn every_test_a_models_table_names_is_a_test_that_exists() {
        /// Every file a test named by a table may live in. A file missing from this list makes a
        /// test look absent, which fails loudly. It can't make an absent one look present.
        const WHERE_TESTS_LIVE: [&str; 30] = [
            include_str!("../../../tests/advanced_tim.rs"),
            include_str!("../../../tests/ak8963.rs"),
            include_str!("../../../tests/dbg.rs"),
            include_str!("../../../tests/dps310.rs"),
            include_str!("../../../tests/flash.rs"),
            include_str!("../../../tests/fram.rs"),
            include_str!("../../../tests/i2c.rs"),
            include_str!("../../../tests/icm20608.rs"),
            include_str!("../../../tests/icm42605.rs"),
            include_str!("../../../tests/icm42688p.rs"),
            include_str!("../../../tests/lis3mdl.rs"),
            include_str!("../../../tests/mpu9250.rs"),
            include_str!("../../../tests/ms5611.rs"),
            include_str!("../../../tests/qmc5883l.rs"),
            include_str!("memory_map.rs"),
            include_str!("../../../tests/dwt.rs"),
            include_str!("peripherals.rs"),
            include_str!("../../../tests/dma.rs"),
            include_str!("../../../tests/gpio.rs"),
            include_str!("../../../tests/iwdg.rs"),
            include_str!("../../../tests/otg.rs"),
            include_str!("../../../tests/pwr.rs"),
            include_str!("../../../tests/rcc.rs"),
            include_str!("../../../tests/rtc.rs"),
            include_str!("../../../tests/sdio.rs"),
            include_str!("../../../tests/soc.rs"),
            include_str!("../../../tests/spi.rs"),
            include_str!("../../../tests/tim.rs"),
            include_str!("../../../tests/usart.rs"),
            include_str!("../../../tests/adc.rs"),
        ];
        const MODELS: [(&str, &str); 28] = [
            ("adc", include_str!("peripherals/adc.rs")),
            ("dbg", include_str!("peripherals/dbg.rs")),
            ("dps310", include_str!("../../chip/dps310.rs")),
            ("nmea", include_str!("../../chip/nmea.rs")),
            ("memory_card", include_str!("../../chip/memory_card.rs")),
            ("ak8963", include_str!("../../chip/ak8963.rs")),
            ("flash", include_str!("peripherals/flash.rs")),
            ("fram", include_str!("../../chip/fram.rs")),
            ("i2c", include_str!("peripherals/i2c.rs")),
            ("icm20608", include_str!("../../chip/icm20608.rs")),
            ("icm42605", include_str!("../../chip/icm42605.rs")),
            ("icm42688p", include_str!("../../chip/icm42688p.rs")),
            ("lis3mdl", include_str!("../../chip/lis3mdl.rs")),
            ("mpu9250", include_str!("../../chip/mpu9250.rs")),
            ("ms5611", include_str!("../../chip/ms5611.rs")),
            ("qmc5883l", include_str!("../../chip/qmc5883l.rs")),
            ("dma", include_str!("peripherals/dma.rs")),
            ("dwt", include_str!("../../cpu/armv7m.rs")),
            ("gpio", include_str!("peripherals/gpio.rs")),
            ("iwdg", include_str!("peripherals/iwdg.rs")),
            ("otg", include_str!("peripherals/otg.rs")),
            ("pwr", include_str!("peripherals/pwr.rs")),
            ("rcc", include_str!("peripherals/rcc.rs")),
            ("rtc", include_str!("peripherals/rtc.rs")),
            ("sdio", include_str!("peripherals/sdio.rs")),
            ("spi", include_str!("peripherals/spi.rs")),
            ("tim", include_str!("peripherals/tim.rs")),
            ("usart", include_str!("peripherals/usart.rs")),
        ];

        let mut named = 0;
        let mut missing = Vec::new();
        for (model, source) in MODELS {
            let sources: Vec<&str> = WHERE_TESTS_LIVE.into_iter().chain([source]).collect();
            let rows = source
                .lines()
                .filter_map(|line| line.strip_prefix("//! |"))
                .filter(|row| !row.starts_with("---"))
                .map(|row| row.split('|').collect::<Vec<&str>>())
                .filter(|cells| cells.len() == 5);
            for cells in rows {
                for name in cells[3].split('`').skip(1).step_by(2) {
                    named += 1;
                    let defined = format!("fn {name}(");
                    if !sources.iter().any(|source| source.contains(&defined)) {
                        missing.push(format!("{model}: {name}"));
                    }
                }
            }
        }
        assert!(named > MODELS.len(), "the tables read as empty");
        assert!(
            missing.is_empty(),
            "a coverage table names a test nothing defines: {}",
            missing.join(", ")
        );
    }

    /// Every request the part wires names a channel and streams the controller has, RM0090 rev 22
    /// section 10.3.3, and an instance the part carries.
    ///
    /// The wiring is a hand-written reading of tables 43 and 44, and a stream or a channel out of range
    /// would otherwise be a panic the first time that peripheral drove a request, in the middle of a run.
    #[test]
    fn every_request_the_part_wires_names_a_channel_and_streams_the_controller_has() {
        use dma::{CHANNELS, STREAMS};

        let soc = super::super::memory_map::builder()
            .build()
            .expect("the part assembles");
        for controller in &CONTROLLERS {
            assert!(
                soc.peripheral(controller.instance).is_some(),
                "{} is not an instance",
                controller.instance
            );
            for wire in controller.wiring {
                assert!(
                    wire.channel < CHANNELS,
                    "{}'s request {} arrives on channel {}",
                    wire.instance,
                    wire.request,
                    wire.channel
                );
                assert!(
                    wire.streams.iter().all(|stream| *stream < STREAMS),
                    "{}'s request {} reaches {:?}",
                    wire.instance,
                    wire.request,
                    wire.streams
                );
                assert!(
                    Field::all()
                        .into_iter()
                        .any(|field| field.instance() == wire.instance),
                    "{} drives a request and is not an instance this part models",
                    wire.instance
                );
            }
        }
    }

    /// [`declared_fields`] is every model's, not the RCC's alone.
    ///
    /// One name from each model that declares any, so dropping a model from that chain is caught rather
    /// than leaving its fields to read as holes in ST's file. The PWR's two are the ones with no other
    /// witness: no firmware names them, so nothing else here would notice them going missing.
    #[test]
    fn the_part_declares_what_each_of_its_models_declares() {
        let names: Vec<&str> = declared_fields().map(|field| field.name).collect();
        for model in ["SW", "GPIOKEN", "MRUDS", "LPUDS"] {
            assert!(
                names.contains(&model),
                "{model} is a model's own and the part does not declare it: {names:?}"
            );
        }
    }

    /// The bit a named field of `RCC_AHB1ENR` occupies, taken from the generated table or from what
    /// a model declares where ST's file leaves the field out. RM0090 rev 22 section 6.3.10.
    fn enable_bit(name: &str) -> u64 {
        use crate::soc::stm32f427::generated::rcc;

        rcc::REGISTERS
            .iter()
            .find(|register| register.name == "AHB1ENR")
            .expect("the clock controller carries it")
            .fields
            .iter()
            .chain(declared_fields())
            .find(|field| field.name == name)
            .unwrap_or_else(|| panic!("{name} is a field nothing declares"))
            .mask()
    }

    /// Turns on all eleven port clocks the way a firmware does, over the bus, since the part gates
    /// each port on its own bit of `RCC_AHB1ENR`. RM0090 rev 22 sections 2.1.11 and 6.3.10.
    fn open_every_port_clock(mcu: &mut Stm32f427) {
        use crate::soc::stm32f427::generated::{RCC, rcc};
        use crate::soc::{Layout, Width};

        let at = RCC.base + u64::from(rcc::Register::Ahb1enr.spec().offset);
        let enables = PORTS
            .iter()
            .fold(0, |all, port| all | enable_bit(&format!("{port}EN")));
        mcu.write(VirtualNanos(0), at, Width::W32, enables)
            .expect("the clock controller holds every enable and nothing gates it");
    }

    /// Every port the part carries has a clock enable, a reset and a sleep-mode enable, at the bit its
    /// place in [`PORTS`] gives. RM0090 rev 22 sections 6.3.10, 6.3.5, and 6.3.15.
    ///
    /// It reads the RCC's table **and** what the models declare, which is the whole point: ST's file
    /// declares ports A to I and stops, so ports J and K are the model's and a check that asked only the
    /// tables would report a part with nine ports and eleven port models.
    #[test]
    fn every_port_has_its_clock_enable_its_reset_and_its_sleep_enable() {
        let mcu = Stm32f427::new().expect("the part assembles");
        let mut declared: BTreeMap<&str, (u8, u8)> = mcu
            .bus()
            .peripheral("RCC")
            .expect("RCC is an instance")
            .registers
            .iter()
            .flat_map(|register| register.fields)
            .map(|field| (field.name, (field.bit, field.width)))
            .collect();
        declared.extend(declared_fields().map(|field| (field.name, (field.bit, field.width))));

        let mut missing = Vec::new();
        for (nth, port) in PORTS.iter().enumerate() {
            let letter = port
                .strip_prefix("GPIO")
                .expect("a port is named for its letter");
            let bit = u8::try_from(nth).expect("eleven ports");
            for suffix in ["EN", "RST", "LPEN"] {
                let name = format!("GPIO{letter}{suffix}");
                if declared.get(name.as_str()) != Some(&(bit, 1)) {
                    missing.push(format!(
                        "{name} at bit {bit}: {:?}",
                        declared.get(name.as_str())
                    ));
                }
            }
        }
        assert!(
            missing.is_empty(),
            "the part carries {} ports and declares fewer sets of RCC bits: {}",
            PORTS.len(),
            missing.join(", ")
        );
    }

    /// Every instance the part models answers behind a clock, except the clock controller, the
    /// backup domain, the debug component, the processor's cycle counter, the flash interface and
    /// the independent watchdog.
    ///
    /// RM0090 rev 22 section 2.1.11 excepts the SRAM and the flash interface, and section 6.2.9
    /// clocks the watchdog from the LSI with no bus enable. So a model added to this part without a
    /// gate beside it is a peripheral that answers before its clock does.
    /// The table of gates is in `memory_map.rs`. This asks the built part rather than that table,
    /// so adding one without the other is what it catches.
    #[test]
    fn every_modeled_instance_but_the_clock_controller_answers_behind_a_clock() {
        use crate::soc::{Fault, Width};

        let mut mcu = Stm32f427::new().expect("the part assembles");
        for field in Field::all() {
            let instance = field.instance();
            let base = mcu
                .bus()
                .peripheral(instance)
                .unwrap_or_else(|| panic!("{instance} is an instance"))
                .base;
            let answered = mcu.read(VirtualNanos(0), base, Width::W32);
            if instance == crate::cpu::armv7m::DWT || instance == "DBG" {
                // Section 6.3 gates what ST built around the core. The processor's own blocks and
                // the debug component, on the core's own private peripheral bus, aren't
                // in it and have no enable to be behind, which is why both answer with the tree
                // untouched.
                assert!(
                    answered.is_ok(),
                    "a core-adjacent block is not on the part's clock tree: {answered:?}"
                );
            } else if instance == "RTC" {
                // Section 5.5.1 bit 8 and section 26.3.5 protect the backup domain against
                // parasitic *write* access. Neither takes its registers dark. `memory_map.rs` gates
                // its writes on `DBP` for that reason and leaves reads alone, which is the same
                // reading the clock controller's own `BDCR` already gets. ArduPilot is the witness:
                // it reads all twenty backup registers with `RTCEN` still clear, and a read gate
                // here would refuse it.
                assert!(
                    answered.is_ok(),
                    "the backup domain is write-protected, not gated: {answered:?}"
                );
            } else if instance == "RCC" {
                assert!(
                    answered.is_ok(),
                    "the clock controller holds every enable, so nothing can gate it: {answered:?}"
                );
            } else if instance == "IWDG" {
                // Sections 6.2.9 and 6.3: the LSI clocks the watchdog, and no AHB or APB enable gates it.
                assert!(
                    answered.is_ok(),
                    "the independent watchdog has no clock gate: {answered:?}"
                );
            } else if instance == "FLASH" {
                assert!(
                    answered.is_ok(),
                    "2.1.11 excepts the flash memory interface as well as the SRAM: {answered:?}"
                );
            } else {
                assert!(
                    matches!(answered, Err(Fault::Gated { .. })),
                    "{instance} answers with every clock still off: {answered:?}"
                );
            }
        }
    }

    /// Each port is its own port: what one drives, no other reads, and what one stores, no other holds.
    ///
    /// The eleven share a layout now, so [`Operate::check`] can't tell one from another. It compares
    /// the model's layout to the slot's and they all match. This is what can: it drives a pin
    /// through one port's own model and reads every port back over the bus. So a `split` handing
    /// over the wrong element, or a slot paired with the wrong register file, shows up as the level
    /// or the value landing somewhere else.
    #[test]
    fn a_port_drives_and_holds_only_its_own() {
        use crate::device::Level;
        use crate::soc::stm32f427::generated::gpioa::Register;
        use crate::soc::{Layout, Width};
        use gpio::Pin;

        let pin = Pin::new(0).expect("a port has a pin zero");
        let idr = u64::from(Register::Idr.spec().offset);
        for (nth, driven) in PORTS.iter().enumerate() {
            let mut mcu = Stm32f427::new().expect("the part assembles");
            open_every_port_clock(&mut mcu);
            mcu.drive_port(VirtualNanos(0), nth, |port, registers, context| {
                port.drive(pin, Some(Level::High), registers, context);
            });
            let sentinel = 1 << nth;
            mcu.port(nth).1.set(Register::Odr, sentinel);
            for (other, name) in PORTS.iter().enumerate() {
                let base = mcu
                    .bus()
                    .peripheral(name)
                    .expect("a port is an instance")
                    .base;
                let read = mcu
                    .read(VirtualNanos(0), base + idr, Width::W32)
                    .expect("IDR answers at its own offset");
                assert_eq!(
                    read & 1,
                    u64::from(other == nth),
                    "{name} reads a pin driven on {driven}"
                );
                let held = mcu
                    .registers(name)
                    .expect("a port is an instance")
                    .get(Register::Odr);
                assert_eq!(
                    held,
                    if other == nth { sentinel } else { 0 },
                    "{name} holds what was stored on {driven}"
                );
            }
        }
    }

    #[test]
    fn every_field_answers_for_the_one_instance_it_is_named_for() {
        let mut mcu = Stm32f427::new().expect("the part assembles");
        let slots = mcu.bus().slots().len();
        let mut answered: Vec<(Field, &'static str)> = (0..slots)
            .filter_map(|slot| {
                let field = mcu.wiring[slot];
                let name = mcu.bus().slots()[slot].peripheral().name;
                mcu.split(slot).1.map(|_| (field, name))
            })
            .collect();
        answered.sort_by_key(|(_, name)| *name);
        let mut expected: Vec<(Field, &'static str)> = Field::all()
            .into_iter()
            .map(|field| (field, field.instance()))
            .collect();
        expected.sort_by_key(|(_, name)| *name);
        assert_eq!(
            answered, expected,
            "every field the part has answers for exactly the instance it is named for"
        );
    }

    #[test]
    fn the_part_answers_for_every_serial_interface_and_neither_extended_block() {
        let carried: Vec<&str> = instances_of(&super::super::generated::spi1::REGISTERS)
            .map(|one| one.name)
            .collect();
        for instance in SERIAL_INTERFACES {
            assert!(
                carried.contains(&instance),
                "{instance} is not an instance of the serial interface's layout"
            );
        }
        // Section 28.4.2 gives these the I2S's job, so the part doesn't answer for them.
        for extended in ["I2S2ext", "I2S3ext"] {
            assert!(carried.contains(&extended));
            assert!(!SERIAL_INTERFACES.contains(&extended));
        }
    }

    #[test]
    fn the_part_says_how_much_of_itself_it_models() {
        let mut mcu = Stm32f427::new().expect("the part assembles");
        let instances = mcu.bus().slots().len();
        let modeled = (0..instances)
            .filter(|&slot| mcu.split(slot).1.is_some())
            .count();
        assert_eq!(modeled, Field::all().len());
        assert!(modeled < instances);
        println!("{modeled} of {instances} instances carry a model");
    }
}