stm32: add executor to low-power mod

embassy-stm32/src/low_power.rs

@@ -1,3 +1,10 @@
+use core::arch::asm;
+use core::marker::PhantomData;
+
+use embassy_executor::*;
+
+const THREAD_PENDER: usize = usize::MAX;
+
 use crate::rtc::{Rtc, RtcInstant};
 
 static mut RTC: Option<&'static Rtc> = None;
@@ -13,3 +20,62 @@ pub fn start_wakeup_alarm(requested_duration: embassy_time::Duration) -> RtcInst
 pub fn stop_wakeup_alarm() -> RtcInstant {
     unsafe { RTC }.unwrap().stop_wakeup_alarm()
 }
+
+/// 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,
+        }
+    }
+
+    fn configure_power(&self) {
+        todo!()
+    }
+
+    /// 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();
+                self.configure_power();
+                asm!("wfe");
+            };
+        }
+    }
+}

embassy-stm32/src/rtc/v2.rs

@@ -162,7 +162,7 @@ impl super::Rtc {
     ///
     /// note: this api is exposed for testing purposes until low power is implemented.
     /// it is not intended to be public
-    pub(crate) fn start_wakeup_alarm(requested_duration: embassy_time::Duration) -> RtcInstant {
+    pub(crate) fn start_wakeup_alarm(&self, requested_duration: embassy_time::Duration) -> RtcInstant {
         use embassy_time::{Duration, TICK_HZ};
 
         use crate::interrupt::typelevel::Interrupt;
@@ -217,7 +217,7 @@ impl super::Rtc {
     ///
     /// note: this api is exposed for testing purposes until low power is implemented.
     /// it is not intended to be public
-    pub(crate) fn stop_wakeup_alarm() -> RtcInstant {
+    pub(crate) fn stop_wakeup_alarm(&self) -> RtcInstant {
         use crate::interrupt::typelevel::Interrupt;
 
         crate::interrupt::typelevel::RTC_WKUP::disable();