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/// VGA text mode console [1]
///
/// 8 colors + 8 bright variants:
/// - 0x0 black (0x8 dark gray)
/// - 0x1 blue (0x9 light blue)
/// - 0x2 green (0xa light green)
/// - 0x3 cyan (0xb light cyan)
/// - 0x4 red (0xc light red)
/// - 0x5 magenta (0xd pink)
/// - 0x6 brown (0xe yellow)
/// - 0x7 light gray (0xf white)
///
/// [1] https://en.wikipedia.org/wiki/VGA_text_mode
pub fn vga(fg: u4, bg: u3) type {
return struct {
const Self = @This();
// Text mode dimensions (mode 3h text mode 80x25).
const COLS = 80;
const ROWS = 25;
// Slice into VGA video memory.
const VIDEO: []u16 = @as([*]u16, @ptrFromInt(0xB8000))[0 .. COLS * ROWS];
/// Current index into last line.
col: usize,
/// Default value.
pub const init: Self = .{
.col = 0,
};
/// Write string to screen and move cursor.
pub fn puts(self: *Self, msg: []const u8) void {
for (msg) |char| {
self.putcImpl(char);
}
self.updateCursor();
}
/// Write character to screen and move cursor.
pub fn putc(self: *Self, char: u8) void {
self.putcImpl(char);
self.updateCursor();
}
/// Write character to screen.
fn putcImpl(self: *Self, char: u8) void {
if (char == '\n') {
self.lf();
return;
}
const idx = (ROWS - 1) * COLS + self.col;
VIDEO[idx] = vgaEntry(char, fg, bg);
self.col += 1;
if (self.col == COLS) {
self.lf();
}
}
/// Handle linefeed (newline).
/// Move up all lines by one, shifting out the upper most line.
fn lf(self: *Self) void {
// Shift all rows one up, copy rows [1. ROWS[-> [0, ROWS-1[.
for (0..(ROWS - 1) * COLS) |idx| {
VIDEO[idx] = VIDEO[1 * COLS + idx];
}
// Clear ROWS-1 (last row).
for (0..COLS) |idx| {
VIDEO[(ROWS - 1) * COLS + idx] = vgaEntry(' ', fg, bg);
}
self.col = 0;
}
/// Update cursor to current position.
/// https://wiki.osdev.org/Text_Mode_Cursor#Without_the_BIOS
fn updateCursor(self: Self) void {
const idx = (ROWS - 1) * COLS + self.col;
outb(0x3d4, 0xf);
outb(0x3d5, @truncate(idx & 0xff));
outb(0x3d4, 0xe);
outb(0x3d5, @truncate(idx >> 8 & 0xff));
}
const Writer = @import("std").io.GenericWriter(*Self, anyerror, struct {
fn write(ctx: *Self, bytes: []const u8) anyerror!usize {
ctx.puts(bytes);
return bytes.len;
}
}.write);
pub fn writer(self: *Self) Writer {
return .{ .context = self };
}
};
}
// Each VGA (text mode) video buffer entry is 16bit wide.
// [15] blink
// [14:12] bg color (3 bit)
// [11: 8] fg color (4 bit)
// [ 7: 0] ascii character
//
// https://en.wikipedia.org/wiki/VGA_text_mode
inline fn vgaEntry(char: u8, fg: u4, bg: u3) u16 {
return @as(u16, bg) << 12 | @as(u16, fg) << 8 | char;
}
inline fn outb(port: u16, val: u8) void {
_ = asm volatile ("outb %[al], %[dx]"
: // no outputs
: [al] "{al}" (val),
[dx] "{dx}" (port),
);
}
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