executor: add Pender, rework Cargo features.

This introduces a `Pender` struct with enum cases for thread-mode, interrupt-mode and
custom callback executors. This avoids calls through function pointers when using only
the thread or interrupt executors. Faster, and friendlier to `cargo-call-stack`.

`embassy-executor` now has `arch-xxx` Cargo features to select the arch and to enable
the builtin executors (thread and interrupt).

2 files changed, 1 insertions, 117 deletions

diff --git a/embassy-cortex-m/src/executor.rs b/embassy-cortex-m/src/executor.rs
deleted file mode 100644
index 558539e73..000000000
--- a/embassy-cortex-m/src/executor.rs
+++ /dev/null
@@ -1,116 +0,0 @@
-//! Executor specific to cortex-m devices.
-
-use core::cell::UnsafeCell;
-use core::mem::MaybeUninit;
-
-use atomic_polyfill::{AtomicBool, Ordering};
-use cortex_m::interrupt::InterruptNumber;
-use cortex_m::peripheral::NVIC;
-pub use embassy_executor::*;
-
-#[derive(Clone, Copy)]
-struct N(u16);
-unsafe impl cortex_m::interrupt::InterruptNumber for N {
-    fn number(self) -> u16 {
-        self.0
-    }
-}
-
-fn pend_by_number(n: u16) {
-    cortex_m::peripheral::NVIC::pend(N(n))
-}
-
-/// 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 InterruptExecutor {
-    started: AtomicBool,
-    executor: UnsafeCell<MaybeUninit<raw::Executor>>,
-}
-
-unsafe impl Send for InterruptExecutor {}
-unsafe impl Sync for InterruptExecutor {}
-
-impl InterruptExecutor {
-    /// 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 InterruptNumber) -> 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(
-                |ctx| pend_by_number(ctx as u16),
-                irq.number() as *mut (),
-            ))
-        }
-
-        let executor = unsafe { (&*self.executor.get()).assume_init_ref() };
-
-        unsafe { NVIC::unmask(irq) }
-
-        executor.spawner().make_send()
-    }
-}
diff --git a/embassy-cortex-m/src/lib.rs b/embassy-cortex-m/src/lib.rs
index fba23367b..e4b713a06 100644
--- a/embassy-cortex-m/src/lib.rs
+++ b/embassy-cortex-m/src/lib.rs
@@ -5,6 +5,6 @@
 // This mod MUST go first, so that the others see its macros.
 pub(crate) mod fmt;
 
-pub mod executor;
+pub use embassy_executor as executor;
 pub mod interrupt;
 pub mod peripheral;