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242 lines
6.6 KiB
Markdown
242 lines
6.6 KiB
Markdown
# Tutorial 03 - Hacky Hello World
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## tl;dr
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Introducing global `print!()` macros to enable "printf debugging" at the
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earliest; To keep tutorial length reasonable, printing functions for now "abuse" a
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QEMU property that lets us use the RPi's `UART` without setting it up properly;
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Using the real hardware `UART` is enabled step-by-step in following tutorials.
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- `interface.rs` is introduced:
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- Provides `Traits` for abstracting `kernel` from `BSP` and `arch` code.
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- Panic handler `print!()`s supplied error messages.
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- This is showcased in `main()`.
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### Give it a try
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QEMU is no longer run in assembly mode. It will from now on show the output of `UART0`.
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```console
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make qemu
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[...]
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Hello from Rust!
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Kernel panic: Stopping here.
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```
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## Diff to previous
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```diff
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diff -uNr 02_runtime_init/Makefile 03_hacky_hello_world/Makefile
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--- 02_runtime_init/Makefile
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+++ 03_hacky_hello_world/Makefile
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@@ -13,7 +13,7 @@
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OUTPUT = kernel8.img
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QEMU_BINARY = qemu-system-aarch64
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QEMU_MACHINE_TYPE = raspi3
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- QEMU_MISC_ARGS = -d in_asm
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+ QEMU_MISC_ARGS = -serial stdio
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LINKER_FILE = src/bsp/rpi/link.ld
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RUSTC_MISC_ARGS = -C target-cpu=cortex-a53
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else ifeq ($(BSP),rpi4)
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@@ -21,7 +21,7 @@
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OUTPUT = kernel8.img
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# QEMU_BINARY = qemu-system-aarch64
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# QEMU_MACHINE_TYPE =
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-# QEMU_MISC_ARGS = -d in_asm
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+# QEMU_MISC_ARGS = -serial stdio
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LINKER_FILE = src/bsp/rpi/link.ld
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RUSTC_MISC_ARGS = -C target-cpu=cortex-a72
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endif
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diff -uNr 02_runtime_init/src/bsp/rpi.rs 03_hacky_hello_world/src/bsp/rpi.rs
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--- 02_runtime_init/src/bsp/rpi.rs
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+++ 03_hacky_hello_world/src/bsp/rpi.rs
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@@ -4,4 +4,35 @@
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//! Board Support Package for the Raspberry Pi.
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-// Coming soon.
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+use crate::interface;
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+use core::fmt;
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+
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+/// A mystical, magical device for generating QEMU output out of the void.
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+struct QEMUOutput;
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+
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+/// Implementing `console::Write` enables usage of the `format_args!` macros, which in turn are used
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+/// to implement the `kernel`'s `print!` and `println!` macros.
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+///
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+/// See [`src/print.rs`].
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+///
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+/// [`src/print.rs`]: ../../print/index.html
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+impl interface::console::Write for QEMUOutput {
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+ fn write_str(&mut self, s: &str) -> fmt::Result {
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+ for c in s.chars() {
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+ unsafe {
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+ core::ptr::write_volatile(0x3F20_1000 as *mut u8, c as u8);
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+ }
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+ }
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+
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+ Ok(())
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+ }
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+}
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+
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+//--------------------------------------------------------------------------------------------------
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+// Implementation of the kernel's BSP calls
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+//--------------------------------------------------------------------------------------------------
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+
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+/// Returns a ready-to-use `console::Write` implementation.
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+pub fn console() -> impl interface::console::Write {
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+ QEMUOutput {}
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+}
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diff -uNr 02_runtime_init/src/interface.rs 03_hacky_hello_world/src/interface.rs
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--- 02_runtime_init/src/interface.rs
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+++ 03_hacky_hello_world/src/interface.rs
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@@ -0,0 +1,36 @@
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+// SPDX-License-Identifier: MIT OR Apache-2.0
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+//
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+// Copyright (c) 2018-2019 Andre Richter <andre.o.richter@gmail.com>
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+
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+//! Trait definitions for coupling `kernel` and `BSP` code.
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+//!
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+//! ```
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+//! +-------------------+
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+//! | Interface (Trait) |
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+//! | |
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+//! +--+-------------+--+
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+//! ^ ^
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+//! | |
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+//! | |
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+//! +----------+--+ +--+----------+
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+//! | Kernel code | | BSP Code |
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+//! | | | |
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+//! +-------------+ +-------------+
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+//! ```
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+
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+/// System console operations.
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+pub mod console {
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+ /// Console write functions.
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+ ///
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+ /// `core::fmt::Write` is exactly what we need for now. Re-export it here because
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+ /// implementing `console::Write` gives a better hint to the reader about the
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+ /// intention.
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+ pub use core::fmt::Write;
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+
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+ /// Console read functions.
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+ pub trait Read {
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+ fn read_char(&mut self) -> char {
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+ ' '
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+ }
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+ }
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+}
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diff -uNr 02_runtime_init/src/main.rs 03_hacky_hello_world/src/main.rs
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--- 02_runtime_init/src/main.rs
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+++ 03_hacky_hello_world/src/main.rs
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@@ -6,9 +6,23 @@
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#![doc(html_logo_url = "https://git.io/JeGIp")]
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//! The `kernel`
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+//!
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+//! The `kernel` is composed by glueing together code from
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+//!
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+//! - [Hardware-specific Board Support Packages] (`BSPs`).
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+//! - [Architecture-specific code].
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+//! - HW- and architecture-agnostic `kernel` code.
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+//!
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+//! using the [`kernel::interface`] traits.
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+//!
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+//! [Hardware-specific Board Support Packages]: bsp/index.html
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+//! [Architecture-specific code]: arch/index.html
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+//! [`kernel::interface`]: interface/index.html
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#![feature(asm)]
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+#![feature(format_args_nl)]
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#![feature(global_asm)]
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+#![feature(panic_info_message)]
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#![no_main]
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#![no_std]
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@@ -22,7 +36,9 @@
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// Conditionally includes the selected `BSP` code.
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mod bsp;
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+mod interface;
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mod panic_wait;
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+mod print;
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/// Early init code.
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///
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@@ -30,5 +46,7 @@
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///
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/// - Only a single core must be active and running this function.
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unsafe fn kernel_init() -> ! {
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- panic!()
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+ println!("Hello from Rust!");
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+
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+ panic!("Stopping here.")
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}
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diff -uNr 02_runtime_init/src/panic_wait.rs 03_hacky_hello_world/src/panic_wait.rs
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--- 02_runtime_init/src/panic_wait.rs
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+++ 03_hacky_hello_world/src/panic_wait.rs
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@@ -4,9 +4,16 @@
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//! A panic handler that infinitely waits.
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+use crate::{arch, println};
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use core::panic::PanicInfo;
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#[panic_handler]
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-fn panic(_info: &PanicInfo) -> ! {
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- crate::arch::wait_forever()
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+fn panic(info: &PanicInfo) -> ! {
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+ if let Some(args) = info.message() {
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+ println!("Kernel panic: {}", args);
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+ } else {
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+ println!("Kernel panic!");
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+ }
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+
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+ arch::wait_forever()
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}
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diff -uNr 02_runtime_init/src/print.rs 03_hacky_hello_world/src/print.rs
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--- 02_runtime_init/src/print.rs
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+++ 03_hacky_hello_world/src/print.rs
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@@ -0,0 +1,33 @@
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+// SPDX-License-Identifier: MIT OR Apache-2.0
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+//
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+// Copyright (c) 2018-2019 Andre Richter <andre.o.richter@gmail.com>
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+
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+//! Printing facilities.
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+
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+use crate::{bsp, interface};
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+use core::fmt;
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+
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+pub fn _print(args: fmt::Arguments) {
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+ use interface::console::Write;
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+
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+ bsp::console().write_fmt(args).unwrap();
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+}
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+
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+/// Prints without a newline.
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+///
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+/// Carbon copy from https://doc.rust-lang.org/src/std/macros.rs.html
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+#[macro_export]
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+macro_rules! print {
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+ ($($arg:tt)*) => ($crate::print::_print(format_args!($($arg)*)));
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+}
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+
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+/// Prints with a newline.
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+///
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+/// Carbon copy from https://doc.rust-lang.org/src/std/macros.rs.html
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+#[macro_export]
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+macro_rules! println {
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+ () => ($crate::print!("\n"));
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+ ($($arg:tt)*) => ({
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+ $crate::print::_print(format_args_nl!($($arg)*));
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+ })
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+}
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```
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