Using it

Let’s write a small program using our driver to write to the serial console.

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

#![no_main]
#![no_std]

mod asm;
mod exceptions;
mod pl011_minimal;

use crate::pl011_minimal::Uart;
use core::fmt::Write;
use core::panic::PanicInfo;
use log::error;
use smccc::Hvc;
use smccc::psci::system_off;

/// Base address of the primary PL011 UART.
const PL011_BASE_ADDRESS: *mut u8 = 0x900_0000 as _;

// SAFETY: There is no other global function of this name.
#[unsafe(no_mangle)]
extern "C" fn main(x0: u64, x1: u64, x2: u64, x3: u64) {
    // SAFETY: `PL011_BASE_ADDRESS` is the base address of a PL011 device, and
    // nothing else accesses that address range.
    let mut uart = unsafe { Uart::new(PL011_BASE_ADDRESS) };

    writeln!(uart, "main({x0:#x}, {x1:#x}, {x2:#x}, {x3:#x})").unwrap();

    system_off::<Hvc>().unwrap();
}