rust-kernel / src / serial.rs

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//! Serial port (UART 16550, COM1 at I/O port 0x3F8).
//! QEMU forwards it to your terminal with `-serial stdio`, which makes it the
//! easiest way to see kernel output without a screen.

use lazy_static::lazy_static;
use spin::Mutex;
use uart_16550::SerialPort;

lazy_static! {
    /// The one global COM1 port, initialised on first use, behind a spinlock.
    pub static ref SERIAL1: Mutex<SerialPort> = {
        let mut port = unsafe { SerialPort::new(0x3F8) };
        port.init();
        Mutex::new(port)
    };
}

#[doc(hidden)]
pub fn _print(args: core::fmt::Arguments) {
    use core::fmt::Write;
    // Disable interrupts while we hold the lock. Otherwise an interrupt
    // handler that also prints would spin forever waiting for a lock held by
    // the code it interrupted (a deadlock).
    x86_64::instructions::interrupts::without_interrupts(|| {
        SERIAL1.lock().write_fmt(args).expect("printing to serial failed");
    });
}

/// Like `print!`, but to the serial port.
#[macro_export]
macro_rules! serial_print {
    ($($arg:tt)*) => ($crate::serial::_print(format_args!($($arg)*)));
}

/// Like `println!`, but to the serial port. Uses "\n" (QEMU passes it through).
#[macro_export]
macro_rules! serial_println {
    () => ($crate::serial_print!("\n"));
    ($fmt:expr) => ($crate::serial_print!(concat!($fmt, "\n")));
    ($fmt:expr, $($arg:tt)*) => ($crate::serial_print!(concat!($fmt, "\n"), $($arg)*));
}