- added a new libary libm containing procedural macros for the kernel.

these should be used to include external files and resources in the kernel binary
  at compile time.
  - libm currently supports loading psf-1 formatted fonts
- added two fonts that are included in the binary at compile time
- refactored libk to make the crate structure more organised and maintainable in future.
  new structure:
    - drivers   (hardware interaction)
    - resources (consts and statics included either manually or via macros)
    - std       (standard functions for higher level interaction with the os, for example creating windows)
- added geometry.rs
  - provides the Vec2<T> struct for use with dimensions, coordinates etc.
- added window.rs
  - provides the Window struct for rendering the state of an application to the screen
- added application.rs
  - provides the Application trait for custom programs to implement in order to run

libk/src/drivers/io/ascii/mod.rs

@@ -0,0 +1,220 @@
+use core::fmt;
+use spin::{Lazy, Mutex};
+use x86_64::instructions::interrupts;
+
+use super::framebuffer::{colour::Colour, display::FRAMEBUFFER_WRITER};
+
+use crate::resources::font::{FONT_CP850_8X16, Font};
+
+static FONT_WIDTH: u32 = 8;
+static FONT_HEIGHT: u32 = 16;
+
+pub static WRITER: Lazy<Mutex<Writer>> = Lazy::new(|| Mutex::new(Writer::new()));
+
+pub fn screensize_chars() -> (u32, u32) {
+    let writer = WRITER.lock();
+    (writer.screen_width, writer.screen_height)
+}
+
+pub struct Writer {
+    font: &'static Font,
+    /// Measured in chars not pixels.
+    screen_width: u32,
+    /// Measured in chars not pixels.
+    screen_height: u32,
+    /// 16 pixels tall.
+    text_line: u32,
+    /// 8 pixels wide.
+    text_col: u32,
+
+    fg_color: Colour,
+    bg_color: Colour,
+
+    offset1: usize,
+    offset2: usize,
+}
+
+impl Default for Writer {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl Writer {
+    pub fn new() -> Self {
+        FRAMEBUFFER_WRITER.lock().as_mut().map_or_else(
+            || {
+                panic!("Framebuffer writer not initialized.");
+            },
+            |writer| Self {
+                font: &FONT_CP850_8X16,
+                screen_width: writer.width() / 8,
+                screen_height: writer.height() / 16,
+                text_line: 0,
+                text_col: 0,
+                fg_color: Colour::White,
+                bg_color: Colour::Black,
+                offset1: 16,
+                offset2: 0,
+            },
+        )
+    }
+
+    pub fn set_font(&mut self, font: &'static Font) {
+        self.font = font;
+    }
+
+    pub fn write_glyph(&mut self, c: u16) {
+        if c as u8 == b'\n' {
+            self.newline();
+            return;
+        }
+
+        // get the character data from the font array. -- each byte is a row of pixels
+        let data: &[u8] = &self.font.0[c as usize];
+
+        if let Some(writer) = FRAMEBUFFER_WRITER.lock().as_mut() {
+            for (row, line) in data.iter().enumerate().take(16) {
+                for col in 0..8 {
+                    let pixel_x: u32 = self.text_col * FONT_WIDTH + col;
+                    let pixel_y: u32 = self.text_line * FONT_HEIGHT + row as u32;
+
+                    if line & (0x80 >> col) != 0 {
+                        // write the foreground color
+                        writer.write_pixel(pixel_x as usize, pixel_y as usize, self.fg_color);
+                    } else {
+                        // write the background color
+                        writer.write_pixel(pixel_x as usize, pixel_y as usize, self.bg_color);
+                    }
+                }
+            }
+        }
+
+        // go to next position
+        if self.text_col + 1 >= self.screen_width {
+            self.newline();
+        } else {
+            self.text_col += 1;
+        }
+    }
+
+    pub const fn set_offset(&mut self, offset1: usize, offset2: usize) {
+        self.offset1 = offset1;
+        self.offset2 = offset2;
+    }
+
+    pub const fn dimensions(&self) -> (u32, u32) {
+        (self.screen_width, self.screen_height)
+    }
+
+    pub const fn next_char(&mut self) {
+        self.text_col += 1;
+    }
+
+    pub const fn newline(&mut self) {
+        self.text_col = 0;
+
+        if self.text_line + 1 >= self.screen_height {
+            self.text_line = 0;
+        } else {
+            self.text_line += 1;
+        }
+    }
+
+    pub fn write_string(&mut self, s: &str) {
+        for c in s.chars() {
+            self.write_glyph(c as u16);
+        }
+    }
+
+    pub const fn set_colour(&mut self, fg: Colour, bg: Colour) {
+        self.fg_color = fg;
+        self.bg_color = bg;
+    }
+
+    pub const fn reset_colour(&mut self) {
+        self.fg_color = Colour::White;
+        self.bg_color = Colour::Black;
+    }
+}
+
+impl core::fmt::Write for Writer {
+    fn write_str(&mut self, s: &str) -> core::fmt::Result {
+        self.write_string(s);
+        Ok(())
+    }
+}
+
+fn write(args: fmt::Arguments, fg: Colour, bg: Colour) {
+    use core::fmt::Write;
+
+    interrupts::without_interrupts(|| {
+        let mut writer = WRITER.lock();
+        writer.set_colour(fg, bg);
+        writer.write_fmt(args).unwrap();
+        writer.reset_colour();
+    });
+}
+
+pub fn _print(args: fmt::Arguments) {
+    x86_64::instructions::interrupts::without_interrupts(|| {
+        write(args, Colour::White, Colour::Black);
+    })
+}
+
+pub fn _print_err(args: fmt::Arguments) {
+    x86_64::instructions::interrupts::without_interrupts(|| {
+        write(args, Colour::Red, Colour::Black);
+    })
+}
+
+pub fn _print_log(args: fmt::Arguments) {
+    x86_64::instructions::interrupts::without_interrupts(|| {
+        write(args, Colour::Yellow, Colour::Black);
+    })
+}
+
+pub fn clear_screen() {
+    interrupts::without_interrupts(|| {
+        let mut writer = WRITER.lock();
+        writer.text_line = 0;
+        writer.text_col = 0;
+
+        if let Some(writer) = FRAMEBUFFER_WRITER.lock().as_mut() {
+            writer.clear();
+        }
+    });
+}
+
+#[macro_export]
+macro_rules! println_log {
+	() => ($crate::print_log!("\n"));
+	($($arg:tt)*) => ($crate::print_log!("{}\n", format_args!($($arg)*)));
+}
+
+#[macro_export]
+macro_rules! print_log {
+	($($arg:tt)*) => ($crate::_print_log(format_args!($($arg)*)));
+}
+
+#[macro_export]
+macro_rules! println {
+	() => ($crate::print!("\n"));
+	($($arg:tt)*) => ($crate::print!("{}\n", format_args!($($arg)*)));
+}
+
+#[macro_export]
+macro_rules! print {
+	($($arg:tt)*) => ($crate::_print(format_args!($($arg)*)));
+}
+
+#[macro_export]
+macro_rules! printlnerr {
+    () => ($crate::printerr!("\n"));
+    ($($arg:tt)*) => ($crate::printerr!("{}\n", format_args!($($arg)*)));
+}
+
+#[macro_export]
+macro_rules! printerr {
+    ($($arg:tt)*) => ($crate::_print_err(format_args!($($arg)*)));
+}

libk/src/drivers/io/framebuffer/colour.rs

@@ -0,0 +1,54 @@
+#[repr(u32)]
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+pub enum Colour {
+    ARGB(u8, u8, u8, u8),
+    RGB(u8, u8, u8),
+    HexARGB(u32),
+    Black = 0x000000FF,
+    Blue = 0x0000FFFF,
+    Green = 0x00FF00FF,
+    Cyan = 0x00FFFFFF,
+    Red = 0xFF0000FF,
+    Magenta = 0xFF00FFFF,
+    Yellow = 0xFFFF00FF,
+    White = 0xFFFFFFFF,
+}
+
+#[allow(clippy::use_self)]
+impl From<Colour> for u32 {
+    fn from(val: Colour) -> Self {
+        match val {
+            Colour::ARGB(a, r, g, b) => {
+                (a as u32) << 24 | (r as u32) << 16 | (g as u32) << 8 | (b as u32)
+            }
+            Colour::RGB(r, g, b) => ((r as u32) << 16) | (g as u32) << 8 | (b as u32),
+            Colour::HexARGB(hex) => hex,
+            Colour::Black => 0xFF000000,
+            Colour::Blue => 0xFF0000FF,
+            Colour::Green => 0xFF00FF00,
+            Colour::Cyan => 0xFF00FFFF,
+            Colour::Red => 0xFFFF0000,
+            Colour::Magenta => 0xFFFF00FF,
+            Colour::Yellow => 0xFFFFFF00,
+            Colour::White => 0xFFFFFFFF,
+        }
+    }
+}
+
+impl core::fmt::Display for Colour {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        match self {
+            Self::ARGB(r, g, b, a) => write!(f, "RGBA(#{:x}{:x}{:x}{:x})", r, g, b, a),
+            Self::RGB(r, g, b) => write!(f, "RGB(#{:x}{:x}{:x})", r, g, b),
+            Self::HexARGB(hex) => write!(f, "Hex(#{:x})", hex),
+            Self::Black => write!(f, "Black"),
+            Self::Blue => write!(f, "Blue"),
+            Self::Green => write!(f, "Green"),
+            Self::Cyan => write!(f, "Cyan"),
+            Self::Red => write!(f, "Red"),
+            Self::Magenta => write!(f, "Magenta"),
+            Self::Yellow => write!(f, "Yellow"),
+            Self::White => write!(f, "White"),
+        }
+    }
+}

libk/src/drivers/io/framebuffer/display.rs

@@ -0,0 +1,97 @@
+use limine::request::FramebufferRequest;
+
+#[used]
+#[unsafe(link_section = ".requests")]
+static FRAMEBUFFER_REQUEST: FramebufferRequest = FramebufferRequest::new();
+
+use super::colour::Colour;
+use core::panic;
+
+use limine::framebuffer::Framebuffer;
+use spin::{Lazy, Mutex};
+
+pub static FRAMEBUFFER_WRITER: Lazy<Mutex<Option<FramebufferWriter>>> = Lazy::new(|| {
+    Mutex::new(FRAMEBUFFER_REQUEST.get_response().map_or_else(
+        || {
+            panic!("Framebuffer request failed");
+        },
+        |framebuffer_response| {
+            let framebuffer = framebuffer_response.framebuffers().next().unwrap();
+            Some(FramebufferWriter::new(framebuffer))
+        },
+    ))
+});
+
+/// The updated writer stores necessary fields from the [Framebuffer].
+/// This ensures that the contained types are Send, as Framebuffer was
+/// not marked as Send.
+///
+/// It also avoids the requirement for lifetimes.
+///
+/// Note this does not implement Writer as these functions only handle drawing pixels.
+pub struct FramebufferWriter {
+    pitch: u64,
+    bpp: u16,
+    addr: *mut u8,
+    width: u64,
+    height: u64,
+}
+
+unsafe impl Send for FramebufferWriter {}
+unsafe impl Sync for FramebufferWriter {}
+
+impl FramebufferWriter {
+    pub fn new(framebuffer: Framebuffer) -> Self {
+        Self {
+            pitch: framebuffer.pitch(),
+            bpp: framebuffer.bpp(),
+            addr: framebuffer.addr(),
+            width: framebuffer.width(),
+            height: framebuffer.height(),
+        }
+    }
+
+    pub fn write_pixel(&self, x: usize, y: usize, color: Colour) {
+        let pitch = self.pitch as usize;
+        let bpp = (self.bpp / 8) as usize;
+        let pixel_offset = y * pitch + x * bpp;
+
+        unsafe {
+            *(self.addr.add(pixel_offset) as *mut u32) = color.into();
+        }
+    }
+
+    pub fn render_frame(&self, buffer: &[Colour; 1280 * 800]) {
+        for (y, row) in buffer.chunks(1280).enumerate() {
+            for (x, pixel) in row.iter().enumerate() {
+                self.write_pixel(x, y, *pixel);
+            }
+        }
+    }
+
+    pub const fn width(&self) -> u32 {
+        self.width as u32
+    }
+
+    pub const fn height(&self) -> u32 {
+        self.height as u32
+    }
+
+    pub fn clear(&self) {
+        let width = self.width as usize;
+        let height = self.height as usize;
+
+        for y in 0..height {
+            for x in 0..width {
+                self.write_pixel(x, y, Colour::Black);
+            }
+        }
+    }
+}
+
+pub fn screensize_px() -> (u32, u32) {
+    FRAMEBUFFER_WRITER
+        .lock()
+        .as_mut()
+        .map_or_else(|| (0, 0), |writer| (writer.width(), writer.height()))
+}

libk/src/drivers/io/framebuffer/mod.rs

@@ -0,0 +1,2 @@
+pub mod colour;
+pub mod display;

libk/src/drivers/io/keyboard.rs

@@ -0,0 +1,81 @@
+use core::{
+    pin::Pin,
+    task::{Context, Poll},
+};
+
+use crossbeam::queue::ArrayQueue;
+use futures_util::{Stream, StreamExt, task::AtomicWaker};
+use pc_keyboard::{DecodedKey, HandleControl, Keyboard, ScancodeSet1, layouts};
+use spin::Once;
+
+use crate::println;
+
+use super::print;
+
+static KBD_QUEUE: Once<ArrayQueue<u8>> = Once::new();
+static WAKER: AtomicWaker = AtomicWaker::new();
+
+pub fn add_scancode(scancode: u8) {
+    if let Some(queue) = KBD_QUEUE.get() {
+        if let Err(_) = queue.push(scancode) {
+            println!("WARNING: scancode queue full; dropping keyboard input");
+        } else {
+            WAKER.wake();
+        }
+    } else {
+        println!("WARNING: scancode queue not initialized");
+    }
+}
+
+pub struct ScancodeStream {
+    _private: (),
+}
+
+impl ScancodeStream {
+    pub fn new() -> Self {
+        KBD_QUEUE.call_once(|| ArrayQueue::new(5));
+        ScancodeStream { _private: () }
+    }
+}
+
+impl Stream for ScancodeStream {
+    type Item = u8;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let queue = KBD_QUEUE.get().unwrap();
+
+        if let Some(scancode) = queue.pop() {
+            return Poll::Ready(Some(scancode));
+        }
+
+        WAKER.register(&cx.waker());
+
+        match queue.pop() {
+            Some(scancode) => {
+                WAKER.take();
+                Poll::Ready(Some(scancode))
+            }
+            None => Poll::Pending,
+        }
+    }
+}
+
+pub async fn print_keypresses() {
+    let mut scancodes = ScancodeStream::new();
+    let mut keyboard = Keyboard::new(
+        ScancodeSet1::new(),
+        layouts::Uk105Key,
+        HandleControl::Ignore,
+    );
+
+    while let Some(scancode) = scancodes.next().await {
+        if let Ok(Some(key_event)) = keyboard.add_byte(scancode) {
+            if let Some(key) = keyboard.process_keyevent(key_event) {
+                match key {
+                    DecodedKey::Unicode(character) => print!("{}", character),
+                    DecodedKey::RawKey(key) => print!("{:?}", key),
+                }
+            }
+        }
+    }
+}

libk/src/drivers/io/mod.rs

@@ -0,0 +1,17 @@
+pub mod ascii;
+pub mod framebuffer;
+pub mod keyboard;
+pub mod port;
+pub mod serial;
+
+// Re-exported macro definitions.
+
+pub use crate::print;
+pub use crate::print_log;
+pub use crate::printerr;
+pub use crate::println;
+pub use crate::println_log;
+pub use crate::printlnerr;
+
+pub use crate::serial_print;
+pub use crate::serial_println;

libk/src/drivers/io/port.rs

@@ -0,0 +1,29 @@
+//! Functions for IO using ports.
+
+use core::arch::asm;
+
+#[inline]
+pub fn inb(port: u16) -> u8 {
+    let value: u8;
+    unsafe {
+        asm!(
+            "in al, dx",
+            out("al") value,
+            in("dx") port,
+            options(nomem, nostack, preserves_flags)
+        );
+    }
+    value
+}
+
+#[inline]
+pub fn outb(port: u16, value: u8) {
+    unsafe {
+        asm!(
+            "out dx, al",
+            in("dx") port,
+            in("al") value,
+            options(nomem, nostack, preserves_flags)
+        );
+    }
+}

libk/src/drivers/io/serial.rs

@@ -0,0 +1,155 @@
+use core::{
+    fmt,
+    sync::atomic::{AtomicUsize, Ordering},
+};
+use spin::{Lazy, Mutex};
+
+#[macro_export]
+macro_rules! serial_print {
+    ($($arg:tt)*) => ($crate::_serial_write(format_args!($($arg)*)));
+}
+
+#[macro_export]
+macro_rules! serial_println {
+    () => ($crate::serial_print!("\n"));
+    ($($arg:tt)*) => (serial_print!("{}\n", format_args!($($arg)*)));
+}
+
+use super::port::{inb, outb};
+
+use x86_64::instructions::interrupts;
+
+pub fn _serial_write(args: fmt::Arguments) {
+    use core::fmt::Write;
+
+    interrupts::without_interrupts(|| {
+        if let Some(writer) = WRITER.lock().as_mut() {
+            writer.write_fmt(args).unwrap();
+        }
+    })
+}
+
+pub fn serial_read() -> &'static str {
+    serial_println!("getting value!");
+
+    interrupts::without_interrupts(|| {
+        if let Some(reader) = READER.lock().as_mut() {
+            serial_println!("stuff happnin.");
+            reader.read_str_to_buffer();
+        } else {
+            serial_println!("failed to get writer");
+        }
+    });
+
+    serial_println!("eee");
+
+    let i = BUFFER_LEN.load(Ordering::SeqCst);
+
+    unsafe {
+        if i != 0 {
+            core::str::from_utf8(&BUFFER[..i - 1]).unwrap()
+        } else {
+            serial_println!("empty string");
+            ""
+        }
+    }
+}
+
+static PORT: u16 = 0x3f8;
+static mut BUFFER: [u8; 256] = [0; 256];
+static BUFFER_LEN: AtomicUsize = AtomicUsize::new(0);
+
+static READER: Lazy<Mutex<Option<Reader>>> = Lazy::new(|| Mutex::new(None));
+static WRITER: Lazy<Mutex<Option<Writer>>> = Lazy::new(|| Mutex::new(None));
+
+struct Reader;
+
+struct Writer;
+
+impl fmt::Write for Writer {
+    fn write_str(&mut self, s: &str) -> fmt::Result {
+        for c in s.chars() {
+            self.write_byte(c as u8);
+        }
+        Ok(())
+    }
+}
+
+impl Writer {
+    unsafe fn write_success(&self) -> bool {
+        inb(PORT + 5) & 0x20 != 0
+    }
+
+    pub fn write_byte(&self, data: u8) {
+        unsafe {
+            while !self.write_success() {}
+            outb(PORT, data);
+        }
+    }
+}
+
+pub fn init() -> Result<(), &'static str> {
+    test()?;
+
+    if READER.lock().is_none() {
+        *READER.lock() = Some(Reader);
+    }
+
+    if WRITER.lock().is_none() {
+        *WRITER.lock() = Some(Writer);
+    }
+
+    Ok(())
+}
+
+pub fn test() -> Result<(), &'static str> {
+    outb(PORT + 1, 0x00); // Disable all interrupts
+    outb(PORT + 3, 0x80); // Enable DLAB (set baud rate divisor)
+    outb(PORT, 0x03); // Set divisor to 3 (lo byte) 38400 baud
+    outb(PORT + 1, 0x00); //                  (hi byte)
+    outb(PORT + 3, 0x03); // 8 bits, no parity, one stop bit
+    outb(PORT + 2, 0xC7); // Enable FIFO, clear them, with 14-bytethreshold
+    outb(PORT + 4, 0x0B); // IRQs enabled, RTS/DSR set
+    outb(PORT + 4, 0x1E); // Set in loopback mode, test the serial chip
+    outb(PORT, 0xAE); // Test serial chip (send byte 0xAE and check if serial returns same byte)
+
+    if inb(PORT) != 0xAE {
+        return Err("serial test failed");
+    }
+
+    outb(PORT + 4, 0x0F);
+
+    Ok(())
+}
+
+impl Reader {
+    pub fn read_str_to_buffer(&mut self) {
+        unsafe {
+            while !self.read_ready() {}
+
+            BUFFER_LEN.store(0, Ordering::SeqCst);
+
+            while BUFFER_LEN.load(Ordering::SeqCst) < 256 {
+                let c = self.read();
+                BUFFER[BUFFER_LEN.load(Ordering::SeqCst)] = c;
+                if c as char == '\r' {
+                    break;
+                }
+                BUFFER_LEN.fetch_add(1, Ordering::SeqCst);
+            }
+
+            serial_println!("returning")
+        }
+    }
+
+    unsafe fn read_ready(&self) -> bool {
+        inb(PORT + 5) & 1 != 0
+    }
+
+    pub fn read(&self) -> u8 {
+        unsafe {
+            while !self.read_ready() {}
+            inb(PORT)
+        }
+    }
+}

libk/src/drivers/kalloc/allocator.rs

@@ -0,0 +1,45 @@
+use linked_list_allocator::LockedHeap;
+use x86_64::{
+    VirtAddr,
+    structures::paging::{
+        FrameAllocator, Mapper, Page, PageTableFlags, Size4KiB, mapper::MapToError,
+    },
+};
+
+/// We are currently using a linked list heap allocator which uses our underlying page allocator.
+pub type FoundryAllocator = LockedHeap;
+
+#[global_allocator]
+/// This is now Rust's global allocator, so we can use stuff requiring heap allocations.
+static ALLOCATOR: FoundryAllocator = FoundryAllocator::empty();
+
+pub const HEAP_START: usize = 0x4444_4444_0000;
+pub const HEAP_SIZE: usize = 1000 * 1024;
+
+/// Sets up the heap using the backing page frame allocator.
+pub fn init_heap(
+    mapper: &mut impl Mapper<Size4KiB>,
+    frame_allocator: &mut impl FrameAllocator<Size4KiB>,
+) -> Result<(), MapToError<Size4KiB>> {
+    let range = {
+        let heap_start = VirtAddr::new(HEAP_START as u64);
+        let heap_end = heap_start + HEAP_SIZE as u64 - 1u64;
+        let heap_start_page = Page::<Size4KiB>::containing_address(heap_start);
+        let heap_end_page = Page::<Size4KiB>::containing_address(heap_end);
+        Page::range_inclusive(heap_start_page, heap_end_page)
+    };
+
+    for page in range {
+        let frame = frame_allocator
+            .allocate_frame()
+            .ok_or(MapToError::FrameAllocationFailed)?;
+        let flags = PageTableFlags::PRESENT | PageTableFlags::WRITABLE;
+        unsafe { mapper.map_to(page, frame, flags, frame_allocator)?.flush() };
+    }
+
+    unsafe {
+        ALLOCATOR.lock().init(HEAP_START as *mut u8, HEAP_SIZE);
+    }
+
+    Ok(())
+}

libk/src/drivers/kalloc/mod.rs

@@ -0,0 +1 @@
+pub mod allocator;

libk/src/drivers/mod.rs

@@ -0,0 +1,3 @@
+pub mod io;
+pub mod kalloc;
+pub mod scheduling;

libk/src/drivers/scheduling/mod.rs

@@ -0,0 +1 @@
+pub mod task;

libk/src/drivers/scheduling/task.rs

@@ -0,0 +1,132 @@
+use alloc::{boxed::Box, collections::BTreeMap, sync::Arc, task::Wake};
+
+use core::sync::atomic::AtomicU64;
+use core::task::Waker;
+use core::task::{Context, Poll};
+use core::{future::Future, pin::Pin};
+use crossbeam::queue::ArrayQueue;
+use x86_64::instructions::interrupts::{self, enable_and_hlt};
+
+pub struct Task {
+    id: TaskId,
+    future: Pin<Box<dyn Future<Output = ()>>>,
+}
+
+impl Task {
+    pub fn new(future: impl Future<Output = ()> + 'static) -> Task {
+        Task {
+            id: TaskId::new(),
+            future: Box::pin(future),
+        }
+    }
+
+    fn poll(&mut self, context: &mut Context) -> Poll<()> {
+        self.future.as_mut().poll(context)
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
+struct TaskId(u64);
+
+impl TaskId {
+    fn new() -> Self {
+        static NEXT: AtomicU64 = AtomicU64::new(0);
+        TaskId(NEXT.fetch_add(1, core::sync::atomic::Ordering::Relaxed))
+    }
+}
+
+pub struct Executor {
+    tasks: BTreeMap<TaskId, Task>,
+    task_queue: Arc<ArrayQueue<TaskId>>,
+    waker_cache: BTreeMap<TaskId, Waker>,
+}
+
+impl Executor {
+    pub fn new() -> Self {
+        Executor {
+            tasks: BTreeMap::new(),
+            task_queue: Arc::new(ArrayQueue::new(100)),
+            waker_cache: BTreeMap::new(),
+        }
+    }
+
+    pub fn spawn(&mut self, task: Task) {
+        let task_id = task.id;
+        if self.tasks.insert(task.id, task).is_some() {
+            panic!("task with same id already in tasks");
+        }
+        self.task_queue.push(task_id).expect("queue full");
+    }
+
+    fn run_ready_tasks(&mut self) {
+        // destructure `self` to avoid borrow checker errors
+        let Self {
+            tasks,
+            task_queue,
+            waker_cache,
+        } = self;
+
+        while let Some(task_id) = task_queue.pop() {
+            let task = match tasks.get_mut(&task_id) {
+                Some(task) => task,
+                None => continue, // task no longer exists
+            };
+            let waker = waker_cache
+                .entry(task_id)
+                .or_insert_with(|| TaskWaker::new(task_id, task_queue.clone()));
+            let mut context = Context::from_waker(waker);
+            match task.poll(&mut context) {
+                Poll::Ready(()) => {
+                    // task done -> remove it and its cached waker
+                    tasks.remove(&task_id);
+                    waker_cache.remove(&task_id);
+                }
+                Poll::Pending => {}
+            }
+        }
+    }
+
+    pub fn run(&mut self) -> ! {
+        loop {
+            self.run_ready_tasks();
+            self.sleep_if_idle();
+        }
+    }
+
+    fn sleep_if_idle(&self) {
+        interrupts::disable();
+        if self.task_queue.is_empty() {
+            enable_and_hlt();
+        } else {
+            interrupts::enable();
+        }
+    }
+}
+
+struct TaskWaker {
+    task_id: TaskId,
+    task_queue: Arc<ArrayQueue<TaskId>>,
+}
+
+impl TaskWaker {
+    fn wake_task(&self) {
+        self.task_queue.push(self.task_id).expect("task_queue full");
+    }
+
+    fn new(task_id: TaskId, task_queue: Arc<ArrayQueue<TaskId>>) -> Waker {
+        Waker::from(Arc::new(TaskWaker {
+            task_id,
+            task_queue,
+        }))
+    }
+}
+
+impl Wake for TaskWaker {
+    fn wake(self: Arc<Self>) {
+        self.wake_task();
+    }
+
+    fn wake_by_ref(self: &Arc<Self>) {
+        self.wake_task();
+    }
+}