michaelkuc6/blog_os
1
0
Fork 0
mirror of https://github.com/phil-opp/blog_os.git synced 2025-12-16 22:37:49 +00:00
Code Issues Projects Releases Wiki Activity

fix broken links in VGA buffer post (#546)

Browse Source
This commit is contained in:
Steve Hess
2019-02-04 04:46:32 -06:00
committed by Philipp Oppermann
parent 426cd9b6a6
commit 82f249ca6f
1 changed files with 10 additions and 10 deletions
Download Patch File Download Diff File Expand all files Collapse all files

20
blog/content/second-edition/posts/03-vga-text-buffer/index.md
View File

@@ -161,8 +161,8 @@ pub struct Writer {
``` ```
The writer will always write to the last line and shift lines up when a line is full (or on `\n`). The `column_position` field keeps track of the current position in the last row. The current foreground and background colors are specified by `color_code` and a reference to the VGA buffer is stored in `buffer`. Note that we need an [explicit lifetime] here to tell the compiler how long the reference is valid. The [`'static`] lifetime specifies that the reference is valid for the whole program run time (which is true for the VGA text buffer). The writer will always write to the last line and shift lines up when a line is full (or on `\n`). The `column_position` field keeps track of the current position in the last row. The current foreground and background colors are specified by `color_code` and a reference to the VGA buffer is stored in `buffer`. Note that we need an [explicit lifetime] here to tell the compiler how long the reference is valid. The [`'static`] lifetime specifies that the reference is valid for the whole program run time (which is true for the VGA text buffer).
[explicit lifetime]: https://doc.rust-lang.org/book/first-edition/lifetimes.html#syntax [explicit lifetime]: https://doc.rust-lang.org/book/ch10-03-lifetime-syntax.html#lifetime-annotation-syntax
[`'static`]: https://doc.rust-lang.org/book/first-edition/lifetimes.html#static [`'static`]: https://doc.rust-lang.org/book/ch10-03-lifetime-syntax.html#the-static-lifetime
### Printing ### Printing
Now we can use the `Writer` to modify the buffer's characters. First we create a method to write a single ASCII byte: Now we can use the `Writer` to modify the buffer's characters. First we create a method to write a single ASCII byte:
@@ -246,8 +246,8 @@ pub fn print_something() {
``` ```
It first creates a new Writer that points to the VGA buffer at `0xb8000`. The syntax for this might seem a bit strange: First, we cast the integer `0xb8000` as an mutable [raw pointer]. Then we convert it to a mutable reference by dereferencing it (through `*`) and immediately borrowing it again (through `&mut`). This conversion requires an [`unsafe` block], since the compiler can't guarantee that the raw pointer is valid. It first creates a new Writer that points to the VGA buffer at `0xb8000`. The syntax for this might seem a bit strange: First, we cast the integer `0xb8000` as an mutable [raw pointer]. Then we convert it to a mutable reference by dereferencing it (through `*`) and immediately borrowing it again (through `&mut`). This conversion requires an [`unsafe` block], since the compiler can't guarantee that the raw pointer is valid.
[raw pointer]: https://doc.rust-lang.org/book/second-edition/ch19-01-unsafe-rust.html#dereferencing-a-raw-pointer [raw pointer]: https://doc.rust-lang.org/book/ch19-01-unsafe-rust.html#dereferencing-a-raw-pointer
[`unsafe` block]: https://doc.rust-lang.org/book/second-edition/ch19-01-unsafe-rust.html#unsafe-rust [`unsafe` block]: https://doc.rust-lang.org/book/ch19-01-unsafe-rust.html
Then it writes the byte `b'H'` to it. The `b` prefix creates a [byte literal], which represents an ASCII character. By writing the strings `"ello "'` and `"Wörld!"`, we test our `write_string` method and the handling of unprintable characters. When we call `vga_buffer::print_something` in our `_start` function (in `src/main.rs`), a `Hello W■■rld!` should be printed in the _lower_ left corner of the screen in yellow: Then it writes the byte `b'H'` to it. The `b` prefix creates a [byte literal], which represents an ASCII character. By writing the strings `"ello "'` and `"Wörld!"`, we test our `write_string` method and the handling of unprintable characters. When we call `vga_buffer::print_something` in our `_start` function (in `src/main.rs`), a `Hello W■■rld!` should be printed in the _lower_ left corner of the screen in yellow:
@@ -297,7 +297,7 @@ struct Buffer {
``` ```
Instead of a `ScreenChar`, we're now using a `Volatile<ScreenChar>`. (The `Volatile` type is [generic] and can wrap (almost) any type). This ensures that we can't accidentally write to it through a “normal” write. Instead, we have to use the `write` method now. Instead of a `ScreenChar`, we're now using a `Volatile<ScreenChar>`. (The `Volatile` type is [generic] and can wrap (almost) any type). This ensures that we can't accidentally write to it through a “normal” write. Instead, we have to use the `write` method now.
[generic]: https://doc.rust-lang.org/book/second-edition/ch10-00-generics.html [generic]: https://doc.rust-lang.org/book/ch10-01-syntax.html
This means that we have to update our `Writer::write_byte` method: This means that we have to update our `Writer::write_byte` method:
@@ -494,11 +494,11 @@ lazy_static! {
However, this `WRITER` is pretty useless since it is immutable. This means that we can't write anything to it (since all the write methods take `&mut self`). One possible solution would be to use a [mutable static]. But then every read and write to it would be unsafe since it could easily introduce data races and other bad things. Using `static mut` is highly discouraged, there were even proposals to [remove it][remove static mut]. But what are the alternatives? We could try to use a immutable static with a cell type like [RefCell] or even [UnsafeCell] that provides [interior mutability]. But these types aren't [Sync] \(with good reason), so we can't use them in statics. However, this `WRITER` is pretty useless since it is immutable. This means that we can't write anything to it (since all the write methods take `&mut self`). One possible solution would be to use a [mutable static]. But then every read and write to it would be unsafe since it could easily introduce data races and other bad things. Using `static mut` is highly discouraged, there were even proposals to [remove it][remove static mut]. But what are the alternatives? We could try to use a immutable static with a cell type like [RefCell] or even [UnsafeCell] that provides [interior mutability]. But these types aren't [Sync] \(with good reason), so we can't use them in statics.
[mutable static]: https://doc.rust-lang.org/book/second-edition/ch19-01-unsafe-rust.html#accessing-or-modifying-a-mutable-static-variable [mutable static]: https://doc.rust-lang.org/book/ch19-01-unsafe-rust.html#accessing-or-modifying-a-mutable-static-variable
[remove static mut]: https://internals.rust-lang.org/t/pre-rfc-remove-static-mut/1437 [remove static mut]: https://internals.rust-lang.org/t/pre-rfc-remove-static-mut/1437
[RefCell]: https://doc.rust-lang.org/nightly/core/cell/struct.RefCell.html [RefCell]: https://doc.rust-lang.org/book/ch15-05-interior-mutability.html#keeping-track-of-borrows-at-runtime-with-refcellt
[UnsafeCell]: https://doc.rust-lang.org/nightly/core/cell/struct.UnsafeCell.html [UnsafeCell]: https://doc.rust-lang.org/nightly/core/cell/struct.UnsafeCell.html
[interior mutability]: https://doc.rust-lang.org/book/first-edition/mutability.html#interior-vs-exterior-mutability [interior mutability]: https://doc.rust-lang.org/book/ch15-05-interior-mutability.html
[Sync]: https://doc.rust-lang.org/nightly/core/marker/trait.Sync.html [Sync]: https://doc.rust-lang.org/nightly/core/marker/trait.Sync.html
### Spinlocks ### Spinlocks
@@ -553,7 +553,7 @@ Note that we only have a single unsafe block in our code, which is needed to cre
### A println Macro ### A println Macro
Now that we have a global writer, we can add a `println` macro that can be used from anywhere in the codebase. Rust's [macro syntax] is a bit strange, so we won't try to write a macro from scratch. Instead we look at the source of the [`println!` macro] in the standard library: Now that we have a global writer, we can add a `println` macro that can be used from anywhere in the codebase. Rust's [macro syntax] is a bit strange, so we won't try to write a macro from scratch. Instead we look at the source of the [`println!` macro] in the standard library:
[macro syntax]: https://doc.rust-lang.org/nightly/book/second-edition/appendix-04-macros.html [macro syntax]: https://doc.rust-lang.org/nightly/book/ch19-06-macros.html#declarative-macros-with-macro_rules-for-general-metaprogramming
[`println!` macro]: https://doc.rust-lang.org/nightly/std/macro.println!.html [`println!` macro]: https://doc.rust-lang.org/nightly/std/macro.println!.html
```rust ```rust
@@ -584,7 +584,7 @@ The macro expands to a call of the [`_print` function] in the `io` module. The [
The [`format_args` macro] builds a [fmt::Arguments] type from the passed arguments, which is passed to `_print`. The [`_print` function] of libstd calls `print_to`, which is rather complicated because it supports different `Stdout` devices. We don't need that complexity since we just want to print to the VGA buffer. The [`format_args` macro] builds a [fmt::Arguments] type from the passed arguments, which is passed to `_print`. The [`_print` function] of libstd calls `print_to`, which is rather complicated because it supports different `Stdout` devices. We don't need that complexity since we just want to print to the VGA buffer.
[`_print` function]: https://github.com/rust-lang/rust/blob/29f5c699b11a6a148f097f82eaa05202f8799bbc/src/libstd/io/stdio.rs#L698 [`_print` function]: https://github.com/rust-lang/rust/blob/29f5c699b11a6a148f097f82eaa05202f8799bbc/src/libstd/io/stdio.rs#L698
[`$crate` variable]: https://doc.rust-lang.org/book/first-edition/macros.html#the-variable-crate [`$crate` variable]: https://doc.rust-lang.org/1.30.0/book/first-edition/macros.html#the-variable-crate
[`format_args` macro]: https://doc.rust-lang.org/nightly/std/macro.format_args.html [`format_args` macro]: https://doc.rust-lang.org/nightly/std/macro.format_args.html
[fmt::Arguments]: https://doc.rust-lang.org/nightly/core/fmt/struct.Arguments.html [fmt::Arguments]: https://doc.rust-lang.org/nightly/core/fmt/struct.Arguments.html