Driver

Now let’s use the new Registers struct in our driver.

// Copyright 2025 Google LLC
// SPDX-License-Identifier: Apache-2.0

use safe_mmio::{UniqueMmioPointer, field, field_shared};

/// Driver for a PL011 UART.
#[derive(Debug)]
pub struct Uart<'a> {
    registers: UniqueMmioPointer<'a, Registers>,
}

impl<'a> Uart<'a> {
    /// Constructs a new instance of the UART driver for a PL011 device with the
    /// given set of registers.
    pub fn new(registers: UniqueMmioPointer<'a, Registers>) -> Self {
        Self { registers }
    }

    /// Writes a single byte to the UART.
    pub fn write_byte(&mut self, byte: u8) {
        // Wait until there is room in the TX buffer.
        while self.read_flag_register().contains(Flags::TXFF) {}

        // Write to the TX buffer.
        field!(self.registers, dr).write(byte.into());

        // Wait until the UART is no longer busy.
        while self.read_flag_register().contains(Flags::BUSY) {}
    }

    /// Reads and returns a pending byte, or `None` if nothing has been
    /// received.
    pub fn read_byte(&mut self) -> Option<u8> {
        if self.read_flag_register().contains(Flags::RXFE) {
            None
        } else {
            let data = field!(self.registers, dr).read();
            // TODO: Check for error conditions in bits 8-11.
            Some(data as u8)
        }
    }

    fn read_flag_register(&self) -> Flags {
        field_shared!(self.registers, fr).read()
    }
}