Printing ASCII character by accessing VGA buffer

Author: alwinsDen

.cargo/config.toml

@@ -5,3 +5,7 @@ build-std-features = ["compiler-builtins-mem"]
 
 [build]
 target = "llvm_target_descp.json"
+
+#using cargo run (add .exe extension)
+[target.'cfg(target_os="none")']
+runner = "bootimage runner"

readme.md

@@ -1,2 +1,4 @@
 <h2>To Run the generated .bin in Qemu emulator.</h2>
-<i>qemu-system-x86_64.exe -drive format=raw,file=bootimage-OS-With-Rust.bin</i>
+<i><span>**RUN:** </span>cargo bootimage<i>
+<br>
+<i><span>**RUN:** </span>qemu-system-x86_64.exe -drive format=raw,file=target\llvm_target_descp\debug\bootimage-OS-With-Rust.bin</i>

src/main.rs

@@ -1,6 +1,8 @@
 #![no_std]
 #![no_main]
 
+mod vga_buffer;
+
 //we will not be using main function as the entrypoint
 use core::panic::PanicInfo;
 
@@ -15,13 +17,14 @@ static HELLO: &[u8] = b"hello world!";
 // no_mangle prevents from function name prined as a crytic
 #[no_mangle]
 pub extern "C" fn _start() -> ! {
-    let vga_buffer = 0xb8000 as *mut u8;
-    for (i, &byte) in HELLO.iter().enumerate() {
-        unsafe {
-            *vga_buffer.offset(i as isize * 2) = byte;
-            *vga_buffer.offset(i as isize * 2 + 1) = 0xb;
-        }
-    }
+    // let vga_buffer = 0xb8000 as *mut u8;
+    // for (i, &byte) in HELLO.iter().enumerate() {
+    //     unsafe {
+    //         *vga_buffer.offset(i as isize * 2) = byte;
+    //         *vga_buffer.offset(i as isize * 2 + 1) = 0xb;
+    //     }
+    // }
+    vga_buffer::print_something();
     loop {}
 }
 

src/vga_buffer.rs

@@ -0,0 +1,99 @@
+#[allow(dead_code)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[repr(u8)] //each enum variant would be stored as a u8.
+pub enum Color {
+    Black = 0,
+    Blue = 1,
+    Green = 2,
+    Cyan = 3,
+    Red = 4,
+    Magenta = 5,
+    Brown = 6,
+    LightGray = 7,
+    DarkGray = 8,
+    LightBlue = 9,
+    LightGreen = 10,
+    LightCyan = 11,
+    LightRed = 12,
+    Pink = 13,
+    Yellow = 14,
+    White = 15,
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+#[repr(transparent)]
+struct ColorCode(u8);
+
+impl ColorCode {
+    fn new(foreground: Color, background: Color) -> ColorCode {
+        ColorCode((background as u8) << 4 | (foreground as u8))
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[repr(C)]
+struct ScreenChar {
+    ascii_character: u8,
+    color_code: ColorCode,
+}
+
+const BUFFER_HEIGHT: usize = 25;
+const BUFFER_WIDTH: usize = 80;
+
+#[repr(transparent)]
+struct Buffer {
+    chars: [[ScreenChar; BUFFER_WIDTH]; BUFFER_HEIGHT],
+}
+
+pub struct Writer {
+    column_position: usize,
+    color_code: ColorCode,
+    buffer: &'static mut Buffer,
+}
+
+impl Writer {
+    pub fn write_byte(&mut self, byte: u8) {
+        match byte {
+            b'\n' => self.new_line(),
+            byte => {
+                if self.column_position >= BUFFER_WIDTH {
+                    self.new_line()
+                }
+                let row = BUFFER_HEIGHT - 1;
+                let col = self.column_position;
+                let color_code = self.color_code;
+
+                self.buffer.chars[row][col] = ScreenChar {
+                    ascii_character: byte,
+                    color_code,
+                };
+                self.column_position += 1;
+            }
+        }
+    }
+    fn new_line(&mut self) {}
+}
+
+impl Writer {
+    pub fn write_string(&mut self, s: &str) {
+        for byte in s.bytes() {
+            match byte {
+                // printable ASCII byte or newline
+                0x20..=0x7e | b'\n' => self.write_byte(byte),
+                // not part of printable ASCII range
+                _ => self.write_byte(0xfe)
+            }
+        }
+    }
+}
+
+pub fn print_something() {
+    let mut writer = Writer {
+        column_position: 0,
+        color_code: ColorCode::new(Color::Yellow, Color::Black),
+        buffer: unsafe { &mut *(0xb8000 as *mut Buffer) },
+    };
+    writer.write_byte(b'H');
+    writer.write_string("ello ");
+    writer.write_string("Wörld!");
+}