use C abi for syscalls

abi_sys/src/lib.rs

@@ -29,63 +29,49 @@ pub enum CallAbiTable {
     GenRand = 5,
 }
 
-pub type PrintAbi = extern "Rust" fn(msg: &str);
+pub type PrintAbi = extern "C" fn(ptr: *const u8, len: usize);
 
 #[allow(unused)]
 pub fn print(msg: &str) {
-    unsafe {
+    let f: PrintAbi = unsafe { core::mem::transmute(CALL_ABI_TABLE[CallAbiTable::Print as usize]) };
-        let ptr = CALL_ABI_TABLE[CallAbiTable::Print as usize];
+    f(msg.as_ptr(), msg.len());
-        let f: PrintAbi = core::mem::transmute(ptr);
-        f(msg);
-    }
 }
 
-pub type SleepAbi = extern "Rust" fn(ms: u64);
+pub type SleepAbi = extern "C" fn(ms: u64);
 
 #[allow(unused)]
 pub fn sleep(ms: u64) {
-    unsafe {
+    let f: SleepAbi = unsafe { core::mem::transmute(CALL_ABI_TABLE[CallAbiTable::Sleep as usize]) };
-        let ptr = CALL_ABI_TABLE[CallAbiTable::Sleep as usize];
-        let f: SleepAbi = core::mem::transmute(ptr);
     f(ms);
-    }
 }
 
-pub type LockDisplay = extern "Rust" fn(lock: bool);
+pub type LockDisplay = extern "C" fn(lock: bool);
 
 #[allow(unused)]
 pub fn lock_display(lock: bool) {
-    unsafe {
+    let f: LockDisplay =
-        let ptr = CALL_ABI_TABLE[CallAbiTable::LockDisplay as usize];
+        unsafe { core::mem::transmute(CALL_ABI_TABLE[CallAbiTable::LockDisplay as usize]) };
-        let f: LockDisplay = core::mem::transmute(ptr);
     f(lock);
-    }
 }
 
-pub type DrawIterAbi = extern "Rust" fn(pixels: &[Pixel<Rgb565>]);
+pub type DrawIterAbi = extern "C" fn(ptr: *const Pixel<Rgb565>, len: usize);
 
 #[allow(unused)]
 pub fn draw_iter(pixels: &[Pixel<Rgb565>]) {
-    unsafe {
+    let f: DrawIterAbi =
-        let ptr = CALL_ABI_TABLE[CallAbiTable::DrawIter as usize];
+        unsafe { core::mem::transmute(CALL_ABI_TABLE[CallAbiTable::DrawIter as usize]) };
-        let f: DrawIterAbi = core::mem::transmute(ptr);
+    f(pixels.as_ptr(), pixels.len());
-        f(pixels);
-    }
 }
 
-pub type GetKeyAbi = extern "Rust" fn() -> Option<KeyEvent>;
+pub type GetKeyAbi = extern "C" fn() -> KeyEvent;
 
 #[allow(unused)]
-pub fn get_key() -> Option<KeyEvent> {
+pub fn get_key() -> KeyEvent {
-    unsafe {
+    let f: GetKeyAbi =
-        let ptr = CALL_ABI_TABLE[CallAbiTable::GetKey as usize];
+        unsafe { core::mem::transmute(CALL_ABI_TABLE[CallAbiTable::GetKey as usize]) };
-        let f: GetKeyAbi = core::mem::transmute(ptr);
     f()
-    }
 }
 
-pub type GenRand = extern "Rust" fn(req: &mut RngRequest);
-
 #[repr(C)]
 pub enum RngRequest {
     U32(u32),
@@ -93,6 +79,8 @@ pub enum RngRequest {
     Bytes { ptr: *mut u8, len: usize },
 }
 
+pub type GenRand = extern "C" fn(req: &mut RngRequest);
+
 #[allow(unused)]
 pub fn gen_rand(req: &mut RngRequest) {
     unsafe {

kernel/src/abi.rs

@@ -1,4 +1,6 @@
-use abi_sys::{DrawIterAbi, GetKeyAbi, LockDisplay, PrintAbi, RngRequest, SleepAbi};
+use abi_sys::{
+    DrawIterAbi, GenRand, GetKeyAbi, LockDisplay, Modifiers, PrintAbi, RngRequest, SleepAbi,
+};
 use core::sync::atomic::Ordering;
 use embassy_rp::clocks::{RoscRng, clk_sys_freq};
 use embedded_graphics::{Pixel, draw_target::DrawTarget, pixelcolor::Rgb565};
@@ -9,18 +11,20 @@ use crate::{
     display::{FB_PAUSED, FRAMEBUFFER},
 };
 
-// ensure the abi and the kernel fn signatures are the same
 const _: PrintAbi = print;
-const _: SleepAbi = sleep;
+pub extern "C" fn print(ptr: *const u8, len: usize) {
-const _: LockDisplay = lock_display;
+    // SAFETY: caller guarantees `ptr` is valid for `len` bytes
-const _: DrawIterAbi = draw_iter;
+    let slice = unsafe { core::slice::from_raw_parts(ptr, len) };
-const _: GetKeyAbi = get_key;
 
-pub extern "Rust" fn print(msg: &str) {
+    if let Ok(msg) = core::str::from_utf8(slice) {
-    defmt::info!("{:?}", msg);
+        defmt::info!("print: {}", msg);
+    } else {
+        defmt::warn!("print: <invalid utf8>");
+    }
 }
 
-pub extern "Rust" fn sleep(ms: u64) {
+const _: SleepAbi = sleep;
+pub extern "C" fn sleep(ms: u64) {
     let cycles_per_ms = clk_sys_freq() / 1000;
     let total_cycles = ms * cycles_per_ms as u64;
 
@@ -29,20 +33,33 @@ pub extern "Rust" fn sleep(ms: u64) {
     }
 }
 
-pub extern "Rust" fn lock_display(lock: bool) {
+const _: LockDisplay = lock_display;
+pub extern "C" fn lock_display(lock: bool) {
     FB_PAUSED.store(lock, Ordering::Relaxed);
 }
 
+const _: DrawIterAbi = draw_iter;
 // TODO: maybe return result
-pub extern "Rust" fn draw_iter(pixels: &[Pixel<Rgb565>]) {
+pub extern "C" fn draw_iter(pixels: *const Pixel<Rgb565>, len: usize) {
+    let pixels = unsafe { core::slice::from_raw_parts(pixels, len) };
     unsafe { FRAMEBUFFER.draw_iter(pixels.iter().copied()).unwrap() }
 }
 
-pub extern "Rust" fn get_key() -> Option<KeyEvent> {
+const _: GetKeyAbi = get_key;
-    unsafe { KEY_CACHE.dequeue() }
+pub extern "C" fn get_key() -> KeyEvent {
+    if let Some(event) = unsafe { KEY_CACHE.dequeue() } {
+        event
+    } else {
+        KeyEvent {
+            key: abi_sys::KeyCode::Unknown(0),
+            state: abi_sys::KeyState::Idle,
+            mods: Modifiers::empty(),
+        }
+    }
 }
 
-pub extern "Rust" fn gen_rand(req: &mut RngRequest) {
+const _: GenRand = gen_rand;
+pub extern "C" fn gen_rand(req: &mut RngRequest) {
     let mut rng = RoscRng;
 
     match req {

shared/src/lib.rs

@@ -14,6 +14,7 @@ pub mod keyboard {
     }
 
     #[derive(Debug)]
+    #[repr(C)]
     pub struct KeyEvent {
         pub key: KeyCode,
         pub state: KeyState,
@@ -22,6 +23,7 @@ pub mod keyboard {
 
     #[cfg_attr(feature = "defmt", derive(defmt::Format))]
     #[derive(Debug, Clone, Copy, PartialEq, Eq)]
+    #[repr(u8)]
     pub enum KeyState {
         Idle = 0,
         Pressed = 1,

user-apps/calculator/src/main.rs

@@ -2,7 +2,7 @@
 #![no_main]
 
 extern crate alloc;
-use abi::{KeyCode, display::Display, get_key, lock_display, print};
+use abi::{KeyCode, KeyState, display::Display, get_key, lock_display, print};
 use alloc::{format, string::String, vec, vec::Vec};
 use core::panic::PanicInfo;
 use embedded_graphics::{
@@ -105,7 +105,8 @@ pub fn main() {
             lock_display(false);
         }
 
-        if let Some(event) = get_key() {
+        let event = get_key();
+        if event.state != KeyState::Idle {
             match event.key {
                 KeyCode::Char(ch) => {
                     input.push(ch);

user-apps/snake/src/main.rs

@@ -3,7 +3,7 @@
 
 extern crate alloc;
 use abi::{
-    KeyCode, Rng,
+    KeyCode, KeyState, Rng,
     display::{Display, SCREEN_HEIGHT, SCREEN_WIDTH},
     get_key, lock_display, print, sleep,
 };
@@ -46,7 +46,8 @@ pub fn main() {
     );
 
     loop {
-        if let Some(event) = get_key() {
+        let event = get_key();
+        if event.state != KeyState::Idle {
             let direction = match event.key {
                 KeyCode::Up => Direction::Up,
                 KeyCode::Down => Direction::Down,
@@ -56,7 +57,7 @@ pub fn main() {
                 _ => Direction::None,
             };
             game.set_direction(direction);
-        }
+        };
 
         // ensure all draws show up at once
         lock_display(true);