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//! STM32-specific `embassy-executor` platform.
//!
//! This module provides an `embassy-executor` platform specific for STM32 chips that integrates [`low_power::sleep()`](crate::low_power::sleep) in the main loop.
//! Read the `embassy-executor` README for information about what "executor platforms" are and how they work.
//!
//! The implementation of the executor platform is equivalent to `platform-cortex-m` in `embassy-executor` other than low-power support.
//!
//! To use it:
//!
//! - Enable feature `executor-thread` and/or `executor-interrupt` in this crate.
//! - **do not** enable features `platform-cortex-m`, `executor-thread` or `executor-interrupt` in the `embassy-executor` crate.
//! - Tell the `main` macro to use this executor like this:
//!
//! ```rust,no_run
//! use embassy_executor::Spawner;
//! use embassy_time::Duration;
//!
//! #[embassy_executor::main(executor = "embassy_stm32::executor::Executor", entry = "cortex_m_rt::entry")]
//! async fn main(spawner: Spawner) {
//! // initialize the platform...
//! let mut config = embassy_stm32::Config::default();
//! // the default value, but can be adjusted
//! config.min_stop_pause = Duration::from_millis(250);
//! // when enabled the power-consumption is much higher during stop, but debugging and RTT is working
//! config.enable_debug_during_sleep = false;
//! let p = embassy_stm32::init(config);
//!
//! // your application here...
//! }
//! ```
#[unsafe(export_name = "__pender")]
#[cfg(any(feature = "executor-thread", feature = "executor-interrupt"))]
fn __pender(context: *mut ()) {
// Safety: `context` is either `usize::MAX` created by `Executor::run`, or a valid interrupt
// request number given to `InterruptExecutor::start`.
let context = context as usize;
#[cfg(feature = "executor-thread")]
// Try to make Rust optimize the branching away if we only use thread mode.
if !cfg!(feature = "executor-interrupt") || context == THREAD_PENDER {
thread::SIGNAL_WORK_THREAD_MODE.store(true, core::sync::atomic::Ordering::SeqCst);
return;
}
#[cfg(feature = "executor-interrupt")]
unsafe {
use cortex_m::interrupt::InterruptNumber;
use cortex_m::peripheral::NVIC;
#[derive(Clone, Copy)]
struct Irq(u16);
unsafe impl InterruptNumber for Irq {
fn number(self) -> u16 {
self.0
}
}
let irq = Irq(context as u16);
// STIR is faster, but is only available in v7 and higher.
#[cfg(not(armv6m))]
{
let mut nvic: NVIC = core::mem::transmute(());
nvic.request(irq);
}
#[cfg(armv6m)]
NVIC::pend(irq);
}
}
#[cfg(feature = "executor-thread")]
pub use thread::*;
#[cfg(feature = "executor-thread")]
mod thread {
pub(super) const THREAD_PENDER: usize = usize::MAX;
use core::marker::PhantomData;
use embassy_executor::{Spawner, raw};
/// global atomic used to keep track of whether there is work to do since sev() is not available on RISCV
pub(crate) static SIGNAL_WORK_THREAD_MODE: core::sync::atomic::AtomicBool =
core::sync::atomic::AtomicBool::new(false);
/// 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 ()>,
}
impl Executor {
/// Create a new Executor.
pub fn new() -> Self {
Self {
inner: raw::Executor::new(THREAD_PENDER as *mut ()),
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();
// we do not care about race conditions between the load and store operations, interrupts
// will only set this value to true.
critical_section::with(|cs| {
// if there is work to do, loop back to polling
if SIGNAL_WORK_THREAD_MODE.load(core::sync::atomic::Ordering::SeqCst) {
SIGNAL_WORK_THREAD_MODE.store(false, core::sync::atomic::Ordering::SeqCst);
} else {
// if not, sleep waiting for interrupt
crate::low_power::sleep(cs);
}
});
// if an interrupt occurred while waiting, it will be serviced here
};
}
}
}
}
#[cfg(feature = "executor-interrupt")]
pub use interrupt::*;
#[cfg(feature = "executor-interrupt")]
mod interrupt {
use core::cell::{Cell, UnsafeCell};
use core::mem::MaybeUninit;
use cortex_m::interrupt::InterruptNumber;
use cortex_m::peripheral::NVIC;
use critical_section::Mutex;
use embassy_executor::raw;
/// 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`](crate::executor::Executor) instead, if it works for your use case.
pub struct InterruptExecutor {
started: Mutex<Cell<bool>>,
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: Mutex::new(Cell::new(false)),
executor: UnsafeCell::new(MaybeUninit::uninit()),
}
}
/// Executor interrupt callback.
///
/// # Safety
///
/// - You MUST call this from the interrupt handler, and from nowhere else.
/// - You must not call this before calling `start()`.
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.
///
/// [`SendSpawner`]: embassy_executor::SendSpawner
pub fn start(&'static self, irq: impl InterruptNumber) -> embassy_executor::SendSpawner {
if critical_section::with(|cs| self.started.borrow(cs).replace(true)) {
panic!("InterruptExecutor::start() called multiple times on the same executor.");
}
unsafe {
(&mut *self.executor.get())
.as_mut_ptr()
.write(raw::Executor::new(irq.number() as *mut ()))
}
let executor = unsafe { (&*self.executor.get()).assume_init_ref() };
unsafe { NVIC::unmask(irq) }
executor.spawner().make_send()
}
/// Get a SendSpawner for this executor
///
/// This returns a [`SendSpawner`](embassy_executor::SendSpawner) you can use to spawn tasks on this
/// executor.
///
/// This MUST only be called on an executor that has already been started.
/// The function will panic otherwise.
pub fn spawner(&'static self) -> embassy_executor::SendSpawner {
if !critical_section::with(|cs| self.started.borrow(cs).get()) {
panic!("InterruptExecutor::spawner() called on uninitialized executor.");
}
let executor = unsafe { (&*self.executor.get()).assume_init_ref() };
executor.spawner().make_send()
}
}
}