2 files changed, 149 insertions, 0 deletions
diff --git a/kernel/src/lib.rs b/kernel/src/lib.rs
index 05b90ef..a27f0a7 100644
--- a/kernel/src/lib.rs
+++ b/kernel/src/lib.rs
@@ -4,8 +4,18 @@
 
 extern crate compiler_builtins;
 
+mod vga_text;
+
+use core::fmt::Write;
+
+
 #[no_mangle]
 pub extern "C" fn _start() -> ! {
+
+    let mut stdout = vga_text::OStream::new();
+    stdout.clear();
+    write!(&mut stdout, "hello world!");
+
     loop {}
 }
 
diff --git a/kernel/src/vga_text.rs b/kernel/src/vga_text.rs
new file mode 100644
index 0000000..ef488e9
--- /dev/null
+++ b/kernel/src/vga_text.rs
@@ -0,0 +1,139 @@
+#[repr(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(Clone, Copy)]
+pub struct CharState(pub u8);
+
+impl CharState {
+    pub fn from_colors(fg: Color, bg: Color) -> Self {
+        Self((fg as u8) | ((bg as u8) << 4))
+    }
+
+    pub fn set_fg(&mut self, fg: Color) {
+        self.0 = (self.0 & 240) | (fg as u8)
+    }
+
+    pub fn set_bg(&mut self, bg: Color) {
+        self.0 = (self.0 & 15) | ((bg as u8) << 4)
+    }
+}
+
+#[derive(Clone, Copy)]
+pub struct VgaChar {
+    pub state: CharState,
+    pub byte: u8
+}
+
+impl VgaChar {
+    pub fn from_state_and_byte(state: CharState, byte: u8) -> Self {
+        Self{ state, byte }
+    }
+}
+
+pub struct OStream {
+    pos: (u8, u8),
+    cursor: *mut VgaChar,
+    state: CharState,
+}
+
+impl OStream {
+    pub fn new() -> Self {
+        Self {
+            pos: (0, 0),
+            cursor: 0xb8000 as *mut VgaChar,
+            state: CharState::from_colors(Color::White, Color::Black)
+        }
+    }
+
+    fn at(n: usize) -> *mut VgaChar {
+        (0xb8000 + (n << 1)) as *mut VgaChar
+    }
+
+    fn compute_cursor(&mut self) {
+        self.cursor = Self::at(self.pos.0 as usize + self.pos.1 as usize * 80)
+    }
+
+    pub fn set_col(&mut self, col: u8) {
+        self.pos.0 = core::cmp::min(col, 79);
+        self.compute_cursor()
+    }
+    
+    pub fn set_row(&mut self, row: u8) {
+        self.pos.1 = core::cmp::min(row, 24);
+        self.compute_cursor()
+    }
+
+    pub fn set_cursor(&mut self, col: u8, row: u8) {
+        self.pos = (core::cmp::min(col, 79), core::cmp::min(row, 24));
+        self.compute_cursor()
+    }
+
+    fn set_char(&mut self, c: VgaChar) {
+        unsafe {self.cursor.write_volatile(c)}
+    }
+
+    pub fn put_char(&mut self, c: VgaChar) {
+        if c.byte == b'\n' {
+            self.new_line();
+        } else if self.pos.0 >= 79 {
+            self.new_line();
+            self.put_char(c);
+        } else {
+            self.set_char(c);
+            self.cursor = self.cursor.wrapping_offset(1);
+            self.pos.0 += 1;
+        }
+    }
+
+    pub fn put_byte(&mut self, b: u8) {
+        self.put_char(VgaChar::from_state_and_byte(self.state, b))
+    }
+
+    pub fn clear(&self) {
+        let c = VgaChar::from_state_and_byte(self.state, b' ');
+        for i in 0..2000 {
+            unsafe {Self::at(i).write_volatile(c)}
+        }
+    }
+
+    pub fn new_line(&mut self) {
+        if self.pos.1 >= 24 {
+            self.set_col(0);
+            for i in 0..1920 {
+                unsafe {Self::at(i).write_volatile(*Self::at(i + 80))}
+            }
+        } else {
+            self.set_cursor(0, self.pos.1 + 1);
+        }
+    }
+
+    pub fn set_state(&mut self, state: CharState) {
+        self.state = state
+    }
+}
+
+impl core::fmt::Write for OStream {
+    fn write_str(&mut self, s: &str) -> core::fmt::Result {
+        for &b in s.as_bytes() {
+            self.put_byte(b)
+        }
+        Ok(())
+    }
+}