1 files changed, 127 insertions, 0 deletions

diff --git a/embassy-executor/src/interrupt.rs b/embassy-executor/src/interrupt.rs
new file mode 100644
index 000000000..f8b0809da
--- /dev/null
+++ b/embassy-executor/src/interrupt.rs
@@ -0,0 +1,127 @@
+//! Interrupt-mode executor.
+
+use core::cell::UnsafeCell;
+use core::mem::MaybeUninit;
+
+use atomic_polyfill::{AtomicBool, Ordering};
+
+use crate::raw::{self, OpaqueInterruptContext, Pender, PenderInner};
+
+/// An interrupt source that can be used to drive an [`InterruptExecutor`].
+// Name pending
+pub trait InterruptContext {
+    /// Creates an opaque identifier for this interrupt.
+    fn context(&self) -> OpaqueInterruptContext;
+
+    /// Sets up the interrupt request.
+    fn enable(&self);
+}
+
+/// Interrupt mode executor.
+///
+/// This executor runs tasks in interrupt mode. The interrupt handler is set up
+/// to poll tasks, and when a task is woken the interrupt is pended from software.
+///
+/// This allows running async tasks at a priority higher than thread mode. One
+/// use case is to leave thread mode free for non-async tasks. Another use case is
+/// to run multiple executors: one in thread mode for low priority tasks and another in
+/// interrupt mode for higher priority tasks. Higher priority tasks will preempt lower
+/// priority ones.
+///
+/// It is even possible to run multiple interrupt mode executors at different priorities,
+/// by assigning different priorities to the interrupts. For an example on how to do this,
+/// See the 'multiprio' example for 'embassy-nrf'.
+///
+/// To use it, you have to pick an interrupt that won't be used by the hardware.
+/// Some chips reserve some interrupts for this purpose, sometimes named "software interrupts" (SWI).
+/// If this is not the case, you may use an interrupt from any unused peripheral.
+///
+/// It is somewhat more complex to use, it's recommended to use the thread-mode
+/// [`Executor`] instead, if it works for your use case.
+pub struct InterruptModeExecutor {
+    started: AtomicBool,
+    executor: UnsafeCell<MaybeUninit<raw::Executor>>,
+}
+
+unsafe impl Send for InterruptModeExecutor {}
+unsafe impl Sync for InterruptModeExecutor {}
+
+impl InterruptModeExecutor {
+    /// Create a new, not started `InterruptExecutor`.
+    #[inline]
+    pub const fn new() -> Self {
+        Self {
+            started: AtomicBool::new(false),
+            executor: UnsafeCell::new(MaybeUninit::uninit()),
+        }
+    }
+
+    /// Executor interrupt callback.
+    ///
+    /// # Safety
+    ///
+    /// You MUST call this from the interrupt handler, and from nowhere else.
+    pub unsafe fn on_interrupt(&'static self) {
+        let executor = unsafe { (&*self.executor.get()).assume_init_ref() };
+        executor.poll();
+    }
+
+    /// Start the executor.
+    ///
+    /// This initializes the executor, enables the interrupt, and returns.
+    /// The executor keeps running in the background through the interrupt.
+    ///
+    /// This returns a [`SendSpawner`] you can use to spawn tasks on it. A [`SendSpawner`]
+    /// is returned instead of a [`Spawner`](embassy_executor::Spawner) because the executor effectively runs in a
+    /// different "thread" (the interrupt), so spawning tasks on it is effectively
+    /// sending them.
+    ///
+    /// To obtain a [`Spawner`](embassy_executor::Spawner) for this executor, use [`Spawner::for_current_executor()`](embassy_executor::Spawner::for_current_executor()) from
+    /// a task running in it.
+    ///
+    /// # Interrupt requirements
+    ///
+    /// You must write the interrupt handler yourself, and make it call [`on_interrupt()`](Self::on_interrupt).
+    ///
+    /// This method already enables (unmasks) the interrupt, you must NOT do it yourself.
+    ///
+    /// You must set the interrupt priority before calling this method. You MUST NOT
+    /// do it after.
+    ///
+    pub fn start(&'static self, irq: impl InterruptContext) -> crate::SendSpawner {
+        if self
+            .started
+            .compare_exchange(false, true, Ordering::Acquire, Ordering::Relaxed)
+            .is_err()
+        {
+            panic!("InterruptExecutor::start() called multiple times on the same executor.");
+        }
+
+        unsafe {
+            (&mut *self.executor.get())
+                .as_mut_ptr()
+                .write(raw::Executor::new(Pender(PenderInner::Interrupt(irq.context()))))
+        }
+
+        let executor = unsafe { (&*self.executor.get()).assume_init_ref() };
+
+        irq.enable();
+
+        executor.spawner().make_send()
+    }
+
+    /// Get a SendSpawner for this executor
+    ///
+    /// This returns a [`SendSpawner`] you can use to spawn tasks on this
+    /// executor.
+    ///
+    /// This MUST only be called on an executor that has already been spawned.
+    /// The function will panic otherwise.
+    pub fn spawner(&'static self) -> crate::SendSpawner {
+        if !self.started.load(Ordering::Acquire) {
+            panic!("InterruptExecutor::spawner() called on uninitialized executor.");
+        }
+        let executor = unsafe { (&*self.executor.get()).assume_init_ref() };
+        executor.spawner().make_send()
+    }
+}