117 lines
4.1 KiB
Rust
117 lines
4.1 KiB
Rust
//! Executor specific to cortex-m devices.
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use core::cell::UnsafeCell;
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use core::mem::MaybeUninit;
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use atomic_polyfill::{AtomicBool, Ordering};
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use cortex_m::interrupt::InterruptNumber;
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use cortex_m::peripheral::NVIC;
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pub use embassy_executor::*;
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#[derive(Clone, Copy)]
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struct N(u16);
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unsafe impl cortex_m::interrupt::InterruptNumber for N {
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fn number(self) -> u16 {
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self.0
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}
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}
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fn pend_by_number(n: u16) {
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cortex_m::peripheral::NVIC::pend(N(n))
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}
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/// Interrupt mode executor.
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///
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/// This executor runs tasks in interrupt mode. The interrupt handler is set up
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/// to poll tasks, and when a task is woken the interrupt is pended from software.
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///
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/// This allows running async tasks at a priority higher than thread mode. One
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/// use case is to leave thread mode free for non-async tasks. Another use case is
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/// to run multiple executors: one in thread mode for low priority tasks and another in
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/// interrupt mode for higher priority tasks. Higher priority tasks will preempt lower
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/// priority ones.
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///
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/// It is even possible to run multiple interrupt mode executors at different priorities,
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/// by assigning different priorities to the interrupts. For an example on how to do this,
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/// See the 'multiprio' example for 'embassy-nrf'.
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///
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/// To use it, you have to pick an interrupt that won't be used by the hardware.
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/// Some chips reserve some interrupts for this purpose, sometimes named "software interrupts" (SWI).
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/// If this is not the case, you may use an interrupt from any unused peripheral.
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///
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/// It is somewhat more complex to use, it's recommended to use the thread-mode
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/// [`Executor`] instead, if it works for your use case.
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pub struct InterruptExecutor {
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started: AtomicBool,
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executor: UnsafeCell<MaybeUninit<raw::Executor>>,
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}
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unsafe impl Send for InterruptExecutor {}
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unsafe impl Sync for InterruptExecutor {}
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impl InterruptExecutor {
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/// Create a new, not started `InterruptExecutor`.
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#[inline]
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pub const fn new() -> Self {
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Self {
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started: AtomicBool::new(false),
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executor: UnsafeCell::new(MaybeUninit::uninit()),
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}
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}
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/// Executor interrupt callback.
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///
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/// # Safety
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///
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/// You MUST call this from the interrupt handler, and from nowhere else.
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pub unsafe fn on_interrupt(&'static self) {
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let executor = unsafe { (&*self.executor.get()).assume_init_ref() };
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executor.poll();
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}
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/// Start the executor.
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///
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/// This initializes the executor, enables the interrupt, and returns.
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/// The executor keeps running in the background through the interrupt.
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///
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/// This returns a [`SendSpawner`] you can use to spawn tasks on it. A [`SendSpawner`]
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/// is returned instead of a [`Spawner`](embassy_executor::Spawner) because the executor effectively runs in a
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/// different "thread" (the interrupt), so spawning tasks on it is effectively
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/// sending them.
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///
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/// To obtain a [`Spawner`](embassy_executor::Spawner) for this executor, use [`Spawner::for_current_executor()`](embassy_executor::Spawner::for_current_executor()) from
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/// a task running in it.
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///
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/// # Interrupt requirements
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///
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/// You must write the interrupt handler yourself, and make it call [`on_interrupt()`](Self::on_interrupt).
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///
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/// This method already enables (unmasks) the interrupt, you must NOT do it yourself.
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///
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/// You must set the interrupt priority before calling this method. You MUST NOT
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/// do it after.
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///
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pub fn start(&'static self, irq: impl InterruptNumber) -> SendSpawner {
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if self
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.started
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.compare_exchange(false, true, Ordering::Acquire, Ordering::Relaxed)
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.is_err()
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{
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panic!("InterruptExecutor::start() called multiple times on the same executor.");
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}
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unsafe {
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(&mut *self.executor.get()).as_mut_ptr().write(raw::Executor::new(
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|ctx| pend_by_number(ctx as u16),
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irq.number() as *mut (),
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))
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}
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let executor = unsafe { (&*self.executor.get()).assume_init_ref() };
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unsafe { NVIC::unmask(irq) }
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executor.spawner().make_send()
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}
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}
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