vga helper

boot1/asm/prelude.s

@@ -338,6 +338,11 @@ prelude_main:
   mov ax, 0x0003
   int 0x10
 
+  ; Disable cursor
+  mov ax, 0x0100
+  mov cx, 0x3f00
+  int 0x10
+
   ; Ensure interrupts are definitely disabled.
   cli
 

boot1/src/main.rs

@@ -1,14 +1,11 @@
 #![no_std]
 #![no_main]
 
-use core::{arch::asm, panic::PanicInfo};
+mod vga;
 
-const VGA_WIDTH: usize = 80;
-const VGA_HEIGHT: usize = 25;
-const VGA_SIZE: usize = VGA_WIDTH * VGA_HEIGHT;
-const VGA_ADDR: usize = 0xb8000;
+use core::{arch::asm, panic::PanicInfo, fmt::Write};
 
-const STR: &[u8] = b"sphinx of black quartz, judge my vow";
+use vga::VgaBuf;
 
 #[repr(C)]
 #[derive(Clone, Debug)]
@@ -35,11 +32,9 @@ fn panic(_info: &PanicInfo) -> ! {
 
 #[no_mangle]
 pub extern "C" fn _start() -> ! {
-  let vga_buf: &'static mut [u16; VGA_SIZE] = unsafe { &mut *(VGA_ADDR as *mut [u16; VGA_SIZE]) };
+  let mut vga_buf = unsafe { VgaBuf::new(0xb8000 as *mut u16) };
 
-  for (i, b) in STR.iter().copied().enumerate() {
-    vga_buf[i] = 0x1f00 | u16::from(b);
-  }
+  writeln!(&mut vga_buf, "hello from rust").ok();
 
   let mut args = BiosIntr {
     eax: 0xe820,
@@ -57,9 +52,7 @@ pub extern "C" fn _start() -> ! {
     _bios_call(0x15, &raw mut args);
   }
 
-  for (i, b) in STR.iter().copied().enumerate() {
-    vga_buf[i + VGA_WIDTH] = 0x1f00 | u16::from(b);
-  }
+  writeln!(&mut vga_buf, "eax = {:x}", args.eax).ok();
 
   hlt()
 }

boot1/src/vga.rs

@@ -0,0 +1,84 @@
+use core::{fmt, ptr};
+
+const VGA_WIDTH: usize = 80;
+const VGA_HEIGHT: usize = 25;
+
+const COLOUR_MASK: u16 = 0x0a00;
+
+pub struct VgaBuf {
+  buf: *mut u16,
+  col: usize,
+  row: usize,
+}
+
+impl VgaBuf {
+  pub unsafe fn new(buf: *mut u16) -> Self {
+    Self { buf, col: 0, row: 0 }
+  }
+
+  pub fn vga_write_str(&mut self, s: &str) {
+    for c in s.chars() {
+      self.vga_write_char(c);
+    }
+  }
+
+  pub fn vga_write_char(&mut self, c: char) {
+    let newline = c == '\n';
+
+    if newline || self.col >= VGA_WIDTH {
+      self.col = 0;
+      self.row += 1;
+    }
+
+    if self.row >= VGA_HEIGHT {
+      self.scroll();
+      self.row -= 1;
+    }
+
+    if !newline {
+      self.vga_write_char_at(c, self.col, self.row);
+      self.col += 1;
+    }
+  }
+
+  pub fn vga_write_ascii_char_at(&mut self, c: u8, col: usize, row: usize) {
+    let vga_val = COLOUR_MASK | u16::from(c);
+
+    if col < VGA_WIDTH && row < VGA_HEIGHT {
+      unsafe {
+        self.coord_ptr(col, row)
+          .write_volatile(vga_val);
+      }
+    }
+  }
+
+  pub fn vga_write_char_at(&mut self, c: char, col: usize, row: usize) {
+    let c = u8::try_from(c).unwrap_or(0xfe);
+    self.vga_write_ascii_char_at(c, col, row);
+  }
+
+  fn scroll(&mut self) {
+    unsafe {
+      ptr::copy(
+        self.coord_ptr(0, 1),
+        self.coord_ptr(0, 0),
+        VGA_WIDTH * (VGA_HEIGHT - 1)
+      );
+      
+      for col in 0..VGA_WIDTH {
+        self.vga_write_ascii_char_at(0, col, VGA_HEIGHT - 1);
+      }
+    }
+  }
+
+  unsafe fn coord_ptr(&self, col: usize, row: usize) -> *mut u16 {
+    unsafe { self.buf.add((row * VGA_WIDTH) + col) }
+  }
+}
+
+impl fmt::Write for VgaBuf {
+  fn write_str(&mut self, s: &str) -> fmt::Result {
+    self.vga_write_str(s);
+    Ok(())
+  }
+}