From 561bef45e771fe5a012805038d0b7750a9beb93d Mon Sep 17 00:00:00 2001
From: Emil Fresk <emil.fresk@gmail.com>
Date: Wed, 3 Aug 2022 11:17:29 +0200
Subject: [PATCH] async idle working

---
 examples/async-idle.rs     | 51 +++++++++++++++++++++++++++++++++++
 macros/src/codegen/idle.rs | 20 +++++++++++---
 src/export.rs              | 54 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 121 insertions(+), 4 deletions(-)
 create mode 100644 examples/async-idle.rs

diff --git a/examples/async-idle.rs b/examples/async-idle.rs
new file mode 100644
index 0000000000..0161a2eca4
--- /dev/null
+++ b/examples/async-idle.rs
@@ -0,0 +1,51 @@
+#![no_main]
+#![no_std]
+#![feature(type_alias_impl_trait)]
+
+use panic_semihosting as _;
+
+// NOTES:
+//
+// - Async tasks cannot have `#[lock_free]` resources, as they can interleve and each async
+//   task can have a mutable reference stored.
+// - Spawning an async task equates to it being polled once.
+
+#[rtic::app(device = lm3s6965, dispatchers = [SSI0, UART0], peripherals = true)]
+mod app {
+    use cortex_m_semihosting::{debug, hprintln};
+    use systick_monotonic::*;
+
+    #[shared]
+    struct Shared {}
+
+    #[local]
+    struct Local {}
+
+    #[monotonic(binds = SysTick, default = true)]
+    type MyMono = Systick<100>;
+
+    #[init]
+    fn init(cx: init::Context) -> (Shared, Local, init::Monotonics) {
+        hprintln!("init").unwrap();
+
+        (
+            Shared {},
+            Local {},
+            init::Monotonics(Systick::new(cx.core.SYST, 12_000_000)),
+        )
+    }
+
+    #[idle]
+    async fn idle(_: idle::Context) -> ! {
+        hprintln!("idle");
+
+        for i in 0..2 {
+            monotonics::delay(100.millis()).await;
+            hprintln!("async delay {}").ok();
+        }
+
+        debug::exit(debug::EXIT_SUCCESS);
+
+        loop {}
+    }
+}
diff --git a/macros/src/codegen/idle.rs b/macros/src/codegen/idle.rs
index 83b85d7ba6..64189a3287 100644
--- a/macros/src/codegen/idle.rs
+++ b/macros/src/codegen/idle.rs
@@ -63,10 +63,15 @@ pub fn codegen(
         let attrs = &idle.attrs;
         let context = &idle.context;
         let stmts = &idle.stmts;
+        let async_ = if idle.is_async {
+            quote!(async)
+        } else {
+            quote!()
+        };
         let user_idle = Some(quote!(
             #(#attrs)*
             #[allow(non_snake_case)]
-            fn #name(#context: #name::Context) -> ! {
+            #async_ fn #name(#context: #name::Context) -> ! {
                 use rtic::Mutex as _;
                 use rtic::mutex::prelude::*;
 
@@ -74,9 +79,16 @@ pub fn codegen(
             }
         ));
 
-        let call_idle = quote!(#name(
-            #name::Context::new(&rtic::export::Priority::new(0))
-        ));
+        let call_idle = if idle.is_async {
+            quote!(
+                let idle_task = #name(#name::Context::new(&rtic::export::Priority::new(0)));
+                rtic::export::idle_executor::IdleExecutor::new(idle_task).run();
+            )
+        } else {
+            quote!(#name(
+                #name::Context::new(&rtic::export::Priority::new(0))
+            ))
+        };
 
         (mod_app, root_idle, user_idle, call_idle)
     } else {
diff --git a/src/export.rs b/src/export.rs
index 08101cdd49..1d17d46b02 100644
--- a/src/export.rs
+++ b/src/export.rs
@@ -21,6 +21,60 @@ pub use heapless::BinaryHeap;
 pub use heapless::Vec;
 pub use rtic_monotonic as monotonic;
 
+pub mod idle_executor {
+    use core::{
+        future::Future,
+        pin::Pin,
+        task::{Context, Poll, RawWaker, RawWakerVTable, Waker},
+    };
+
+    fn no_op(_: *const ()) {}
+    fn no_op_clone(_: *const ()) -> RawWaker {
+        noop_raw_waker()
+    }
+
+    static IDLE_WAKER_TABLE: RawWakerVTable = RawWakerVTable::new(no_op_clone, no_op, no_op, no_op);
+
+    #[inline]
+    fn noop_raw_waker() -> RawWaker {
+        RawWaker::new(core::ptr::null(), &IDLE_WAKER_TABLE)
+    }
+
+    pub struct IdleExecutor<T>
+    where
+        T: Future,
+    {
+        idle: T,
+    }
+
+    impl<T> IdleExecutor<T>
+    where
+        T: Future,
+    {
+        #[inline(always)]
+        pub fn new(idle: T) -> Self {
+            Self { idle }
+        }
+
+        #[inline(always)]
+        pub fn run(&mut self) -> ! {
+            let w = unsafe { Waker::from_raw(noop_raw_waker()) };
+            let mut ctxt = Context::from_waker(&w);
+            loop {
+                match unsafe { Pin::new_unchecked(&mut self.idle) }.poll(&mut ctxt) {
+                    Poll::Pending => {
+                        // All ok!
+                    }
+                    Poll::Ready(_) => {
+                        // The idle executor will never return
+                        unreachable!()
+                    }
+                }
+            }
+        }
+    }
+}
+
 pub mod executor {
     use core::{
         future::Future,