| // Copyright 2022, The Android Open Source Project |
| // |
| // Licensed under the Apache License, Version 2.0 (the "License"); |
| // you may not use this file except in compliance with the License. |
| // You may obtain a copy of the License at |
| // |
| // http://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS IS" BASIS, |
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| // See the License for the specific language governing permissions and |
| // limitations under the License. |
| |
| //! Minimal driver for an 8250 UART. This only implements enough to work with the emulated 8250 |
| //! provided by crosvm, and won't work with real hardware. |
| |
| use core::fmt::{self, Write}; |
| use core::ptr::write_volatile; |
| |
| /// Minimal driver for an 8250 UART. This only implements enough to work with the emulated 8250 |
| /// provided by crosvm, and won't work with real hardware. |
| pub struct Uart { |
| base_address: *mut u8, |
| } |
| |
| impl Uart { |
| /// Constructs a new instance of the UART driver for a device at the given base address. |
| /// |
| /// # Safety |
| /// |
| /// The given base address must point to the 8 MMIO control registers of an appropriate UART |
| /// device, which must be mapped into the address space of the process as device memory and not |
| /// have any other aliases. |
| pub unsafe fn new(base_address: usize) -> Self { |
| Self { base_address: base_address as *mut u8 } |
| } |
| |
| /// Writes a single byte to the UART. |
| pub fn write_byte(&self, byte: u8) { |
| // Safe because we know that the base address points to the control registers of an UART |
| // device which is appropriately mapped. |
| unsafe { |
| write_volatile(self.base_address, byte); |
| } |
| } |
| } |
| |
| impl Write for Uart { |
| fn write_str(&mut self, s: &str) -> fmt::Result { |
| for c in s.as_bytes() { |
| self.write_byte(*c); |
| } |
| Ok(()) |
| } |
| } |
| |
| // Safe because it just contains a pointer to device memory, which can be accessed from any context. |
| unsafe impl Send for Uart {} |