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executor: add Pender, rework Cargo features.

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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).
This commit is contained in:
Dario Nieuwenhuis
2023-04-03 01:18:27 +02:00
parent b41ee47115
commit d3c4e4a20a
50 changed files with 667 additions and 522 deletions
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242
embassy-executor/src/arch/cortex_m.rs
View File

@ -1,59 +1,209 @@
use core::arch::asm;
use core::marker::PhantomData;
use core::ptr;
#[cfg(feature = "executor-thread")]
pub use thread::*;
#[cfg(feature = "executor-thread")]
mod thread {
use core::arch::asm;
use core::marker::PhantomData;
use super::{raw, Spawner};
#[cfg(feature = "nightly")]
pub use embassy_macros::main_cortex_m as main;
/// Thread mode executor, using WFE/SEV.
///
/// This is the simplest and most common kind of executor. It runs on
/// thread mode (at the lowest priority level), and uses the `WFE` ARM instruction
/// to sleep when it has no more work to do. When a task is woken, a `SEV` instruction
/// is executed, to make the `WFE` exit from sleep and poll the task.
///
/// This executor allows for ultra low power consumption for chips where `WFE`
/// triggers low-power sleep without extra steps. If your chip requires extra steps,
/// you may use [`raw::Executor`] directly to program custom behavior.
pub struct Executor {
inner: raw::Executor,
not_send: PhantomData<*mut ()>,
}
use crate::raw::{Pender, PenderInner};
use crate::{raw, Spawner};
impl Executor {
/// Create a new Executor.
pub fn new() -> Self {
Self {
inner: raw::Executor::new(|_| unsafe { asm!("sev") }, ptr::null_mut()),
not_send: PhantomData,
#[derive(Copy, Clone)]
pub(crate) struct ThreadPender;
impl ThreadPender {
pub(crate) fn pend(self) {
unsafe { core::arch::asm!("sev") }
}
}
/// Run the executor.
/// Thread mode executor, using WFE/SEV.
///
/// The `init` closure is called with a [`Spawner`] that spawns tasks on
/// this executor. Use it to spawn the initial task(s). After `init` returns,
/// the executor starts running the tasks.
/// This is the simplest and most common kind of executor. It runs on
/// thread mode (at the lowest priority level), and uses the `WFE` ARM instruction
/// to sleep when it has no more work to do. When a task is woken, a `SEV` instruction
/// is executed, to make the `WFE` exit from sleep and poll the task.
///
/// To spawn more tasks later, you may keep copies of the [`Spawner`] (it is `Copy`),
/// for example by passing it as an argument to the initial tasks.
///
/// This function requires `&'static mut self`. This means you have to store the
/// Executor instance in a place where it'll live forever and grants you mutable
/// access. There's a few ways to do this:
///
/// - a [StaticCell](https://docs.rs/static_cell/latest/static_cell/) (safe)
/// - a `static mut` (unsafe)
/// - a local variable in a function you know never returns (like `fn main() -> !`), upgrading its lifetime with `transmute`. (unsafe)
///
/// This function never returns.
pub fn run(&'static mut self, init: impl FnOnce(Spawner)) -> ! {
init(self.inner.spawner());
/// This executor allows for ultra low power consumption for chips where `WFE`
/// triggers low-power sleep without extra steps. If your chip requires extra steps,
/// you may use [`raw::Executor`] directly to program custom behavior.
pub struct Executor {
inner: raw::Executor,
not_send: PhantomData<*mut ()>,
}
impl Executor {
/// Create a new Executor.
pub fn new() -> Self {
Self {
inner: raw::Executor::new(Pender(PenderInner::Thread(ThreadPender))),
not_send: PhantomData,
}
}
/// Run the executor.
///
/// The `init` closure is called with a [`Spawner`] that spawns tasks on
/// this executor. Use it to spawn the initial task(s). After `init` returns,
/// the executor starts running the tasks.
///
/// To spawn more tasks later, you may keep copies of the [`Spawner`] (it is `Copy`),
/// for example by passing it as an argument to the initial tasks.
///
/// This function requires `&'static mut self`. This means you have to store the
/// Executor instance in a place where it'll live forever and grants you mutable
/// access. There's a few ways to do this:
///
/// - a [StaticCell](https://docs.rs/static_cell/latest/static_cell/) (safe)
/// - a `static mut` (unsafe)
/// - a local variable in a function you know never returns (like `fn main() -> !`), upgrading its lifetime with `transmute`. (unsafe)
///
/// This function never returns.
pub fn run(&'static mut self, init: impl FnOnce(Spawner)) -> ! {
init(self.inner.spawner());
loop {
unsafe {
self.inner.poll();
asm!("wfe");
};
}
}
}
}
#[cfg(feature = "executor-interrupt")]
pub use interrupt::*;
#[cfg(feature = "executor-interrupt")]
mod interrupt {
use core::cell::UnsafeCell;
use core::mem::MaybeUninit;
use atomic_polyfill::{AtomicBool, Ordering};
use cortex_m::interrupt::InterruptNumber;
use cortex_m::peripheral::NVIC;
use crate::raw::{self, Pender, PenderInner};
#[derive(Clone, Copy)]
pub(crate) struct InterruptPender(u16);
impl InterruptPender {
pub(crate) fn pend(self) {
// STIR is faster, but is only available in v7 and higher.
#[cfg(not(armv6m))]
{
let mut nvic: cortex_m::peripheral::NVIC = unsafe { core::mem::transmute(()) };
nvic.request(self);
}
#[cfg(armv6m)]
cortex_m::peripheral::NVIC::pend(self);
}
}
unsafe impl cortex_m::interrupt::InterruptNumber for InterruptPender {
fn number(self) -> u16 {
self.0
}
}
/// 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) -> 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.");
}
loop {
unsafe {
self.inner.poll();
asm!("wfe");
};
(&mut *self.executor.get())
.as_mut_ptr()
.write(raw::Executor::new(Pender(PenderInner::Interrupt(InterruptPender(
irq.number(),
)))))
}
let executor = unsafe { (&*self.executor.get()).assume_init_ref() };
unsafe { NVIC::unmask(irq) }
executor.spawner().make_send()
}
}
}