14 files changed, 72 insertions, 170 deletions

diff --git a/embassy-stm32/CHANGELOG.md b/embassy-stm32/CHANGELOG.md
index df832d15f..8e3e802a4 100644
--- a/embassy-stm32/CHANGELOG.md
+++ b/embassy-stm32/CHANGELOG.md
@@ -7,6 +7,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased - ReleaseDate
 
+- feat: allow embassy_executor::main for low power
 - feat: Add waveform methods to ComplementaryPwm
 - fix: Avoid generating timer update events when updating the frequency ([#4890](https://github.com/embassy-rs/embassy/pull/4890))
 - chore: cleanup low-power add time
diff --git a/embassy-stm32/src/lib.rs b/embassy-stm32/src/lib.rs
index 6e492946a..7c3770643 100644
--- a/embassy-stm32/src/lib.rs
+++ b/embassy-stm32/src/lib.rs
@@ -649,10 +649,7 @@ fn init_hw(config: Config) -> Peripherals {
             rcc::init_rcc(cs, config.rcc);
 
             #[cfg(feature = "low-power")]
-            crate::rtc::init_rtc(cs, config.rtc);
-
-            #[cfg(feature = "low-power")]
-            crate::time_driver::get_driver().set_min_stop_pause(cs, config.min_stop_pause);
+            rtc::init_rtc(cs, config.rtc, config.min_stop_pause);
         }
 
         p
diff --git a/embassy-stm32/src/low_power.rs b/embassy-stm32/src/low_power.rs
index 36c7e2242..cf8f2b393 100644
--- a/embassy-stm32/src/low_power.rs
+++ b/embassy-stm32/src/low_power.rs
@@ -14,7 +14,7 @@
 //!
 //! Since entering and leaving low-power modes typically incurs a significant latency, the
 //! low-power executor will only attempt to enter when the next timer event is at least
-//! [`time_driver::MIN_STOP_PAUSE`] in the future.
+//! [`time_driver::min_stop_pause`] in the future.
 //!
 //! Currently there is no macro analogous to `embassy_executor::main` for this executor;
 //! consequently one must define their entrypoint manually. Moreover, you must relinquish control
@@ -22,21 +22,16 @@
 //!
 //! ```rust,no_run
 //! use embassy_executor::Spawner;
-//! use embassy_stm32::low_power::Executor;
+//! use embassy_stm32::low_power;
 //! use embassy_stm32::rtc::{Rtc, RtcConfig};
-//! use static_cell::StaticCell;
+//! use embassy_time::Duration;
 //!
-//! #[cortex_m_rt::entry]
-//! fn main() -> ! {
-//!     Executor::take().run(|spawner| {
-//!         spawner.spawn(unwrap!(async_main(spawner)));
-//!     });
-//! }
-//!
-//! #[embassy_executor::task]
+//! #[embassy_executor::main(executor = "low_power::Executor")]
 //! async fn async_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);
@@ -45,11 +40,9 @@
 //! }
 //! ```
 
-// TODO: Usage of `static mut` here is unsound. Fix then remove this `allow`.`
-#![allow(static_mut_refs)]
-
 use core::arch::asm;
 use core::marker::PhantomData;
+use core::mem;
 use core::sync::atomic::{Ordering, compiler_fence};
 
 use cortex_m::peripheral::SCB;
@@ -57,11 +50,12 @@ use critical_section::CriticalSection;
 use embassy_executor::*;
 
 use crate::interrupt;
+use crate::rcc::{REFCOUNT_STOP1, REFCOUNT_STOP2};
 use crate::time_driver::get_driver;
 
 const THREAD_PENDER: usize = usize::MAX;
 
-static mut EXECUTOR: Option<Executor> = None;
+static mut EXECUTOR_TAKEN: bool = false;
 
 /// Prevent the device from going into the stop mode if held
 pub struct DeviceBusy(StopMode);
@@ -182,42 +176,47 @@ impl Into<Lpms> for StopMode {
 pub struct Executor {
     inner: raw::Executor,
     not_send: PhantomData<*mut ()>,
-    scb: SCB,
 }
 
 impl Executor {
     /// Create a new Executor.
-    pub fn take() -> &'static mut Self {
-        critical_section::with(|_| unsafe {
-            assert!(EXECUTOR.is_none());
-
-            EXECUTOR = Some(Self {
-                inner: raw::Executor::new(THREAD_PENDER as *mut ()),
-                not_send: PhantomData,
-                scb: cortex_m::Peripherals::steal().SCB,
-            });
-
-            let executor = EXECUTOR.as_mut().unwrap();
+    pub fn new() -> Self {
+        unsafe {
+            if EXECUTOR_TAKEN {
+                panic!("Low power executor can only be taken once.");
+            } else {
+                EXECUTOR_TAKEN = true;
+            }
+        }
 
-            executor
-        })
+        Self {
+            inner: raw::Executor::new(THREAD_PENDER as *mut ()),
+            not_send: PhantomData,
+        }
     }
 
     pub(crate) unsafe fn on_wakeup_irq() {
         critical_section::with(|cs| {
             #[cfg(stm32wlex)]
             {
-                let extscr = crate::pac::PWR.extscr().read();
+                use crate::pac::rcc::vals::Sw;
+                use crate::pac::{PWR, RCC};
+                use crate::rcc::{RCC_CONFIG, init as init_rcc};
+
+                let extscr = PWR.extscr().read();
                 if extscr.c1stop2f() || extscr.c1stopf() {
                     // when we wake from any stop mode we need to re-initialize the rcc
-                    crate::rcc::apply_resume_config();
+                    while RCC.cfgr().read().sws() != Sw::MSI {}
+
+                    init_rcc(RCC_CONFIG.unwrap());
+
                     if extscr.c1stop2f() {
                         // when we wake from STOP2, we need to re-initialize the time driver
-                        crate::time_driver::init_timer(cs);
+                        get_driver().init_timer(cs);
                         // reset the refcounts for STOP2 and STOP1 (initializing the time driver will increment one of them for the timer)
                         // and given that we just woke from STOP2, we can reset them
-                        crate::rcc::REFCOUNT_STOP2 = 0;
-                        crate::rcc::REFCOUNT_STOP1 = 0;
+                        REFCOUNT_STOP2 = 0;
+                        REFCOUNT_STOP1 = 0;
                     }
                 }
             }
@@ -226,11 +225,15 @@ impl Executor {
         });
     }
 
+    const fn get_scb() -> SCB {
+        unsafe { mem::transmute(()) }
+    }
+
     fn stop_mode(_cs: CriticalSection) -> Option<StopMode> {
-        if unsafe { crate::rcc::REFCOUNT_STOP2 == 0 && crate::rcc::REFCOUNT_STOP1 == 0 } {
+        if unsafe { REFCOUNT_STOP2 == 0 && REFCOUNT_STOP1 == 0 } {
             trace!("low power: stop 2");
             Some(StopMode::Stop2)
-        } else if unsafe { crate::rcc::REFCOUNT_STOP1 == 0 } {
+        } else if unsafe { REFCOUNT_STOP1 == 0 } {
             trace!("low power: stop 1");
             Some(StopMode::Stop1)
         } else {
@@ -240,7 +243,7 @@ impl Executor {
     }
 
     #[allow(unused_variables)]
-    fn configure_stop(&mut self, stop_mode: StopMode) {
+    fn configure_stop(&self, stop_mode: StopMode) {
         #[cfg(any(stm32l4, stm32l5, stm32u5, stm32u0, stm32wba, stm32wlex))]
         crate::pac::PWR.cr1().modify(|m| m.set_lpms(stop_mode.into()));
         #[cfg(stm32h5)]
@@ -251,8 +254,8 @@ impl Executor {
         });
     }
 
-    fn configure_pwr(&mut self) {
-        self.scb.clear_sleepdeep();
+    fn configure_pwr(&self) {
+        Self::get_scb().clear_sleepdeep();
         // Clear any previous stop flags
         #[cfg(stm32wlex)]
         crate::pac::PWR.extscr().modify(|w| {
@@ -271,7 +274,7 @@ impl Executor {
             self.configure_stop(stop_mode);
 
             #[cfg(not(feature = "low-power-debug-with-sleep"))]
-            self.scb.set_sleepdeep();
+            Self::get_scb().set_sleepdeep();
         });
     }
 
@@ -294,12 +297,11 @@ impl Executor {
     ///
     /// This function never returns.
     pub fn run(&'static mut self, init: impl FnOnce(Spawner)) -> ! {
-        let executor = unsafe { EXECUTOR.as_mut().unwrap() };
-        init(executor.inner.spawner());
+        init(self.inner.spawner());
 
         loop {
             unsafe {
-                executor.inner.poll();
+                self.inner.poll();
                 self.configure_pwr();
                 asm!("wfe");
                 #[cfg(stm32wlex)]
diff --git a/embassy-stm32/src/rcc/l.rs b/embassy-stm32/src/rcc/l.rs
index 584957c6d..2e1cbd702 100644
--- a/embassy-stm32/src/rcc/l.rs
+++ b/embassy-stm32/src/rcc/l.rs
@@ -1,6 +1,3 @@
-#[cfg(all(feature = "low-power", stm32wlex))]
-use core::mem::MaybeUninit;
-
 #[cfg(any(stm32l0, stm32l1))]
 pub use crate::pac::pwr::vals::Vos as VoltageScale;
 use crate::pac::rcc::regs::Cfgr;
@@ -14,42 +11,6 @@ use crate::time::Hertz;
 /// HSI speed
 pub const HSI_FREQ: Hertz = Hertz(16_000_000);
 
-/// Saved RCC Config
-///
-/// Used when exiting STOP2 to re-enable clocks to their last configured state
-/// for chips that need it.
-#[cfg(all(feature = "low-power", stm32wlex))]
-static mut RESUME_RCC_CONFIG: MaybeUninit<Config> = MaybeUninit::uninit();
-
-/// Set the rcc config to be restored when exiting STOP2
-///
-/// Safety: Sets a mutable global.
-#[cfg(all(feature = "low-power", stm32wlex))]
-pub(crate) unsafe fn set_resume_config(config: Config) {
-    trace!("rcc set_resume_config()");
-    RESUME_RCC_CONFIG = MaybeUninit::new(config);
-}
-
-/// Get the rcc config to be restored when exiting STOP2
-///
-/// Safety: Reads a mutable global.
-#[cfg(all(feature = "low-power", stm32wlex))]
-pub(crate) unsafe fn get_resume_config() -> Config {
-    *(*core::ptr::addr_of_mut!(RESUME_RCC_CONFIG)).assume_init_ref()
-}
-
-#[cfg(all(feature = "low-power", stm32wlex))]
-/// Safety: should only be called from low power executable just after resuming from STOP2
-pub(crate) unsafe fn apply_resume_config() {
-    trace!("rcc apply_resume_config()");
-
-    while RCC.cfgr().read().sws() != Sysclk::MSI {}
-
-    let config = get_resume_config();
-
-    init(config);
-}
-
 #[derive(Clone, Copy, Eq, PartialEq)]
 pub enum HseMode {
     /// crystal/ceramic oscillator (HSEBYP=0)
@@ -193,10 +154,6 @@ fn msi_enable(range: MSIRange) {
 }
 
 pub(crate) unsafe fn init(config: Config) {
-    // save the rcc config because if we enter stop 2 we need to re-apply it on wakeup
-    #[cfg(all(feature = "low-power", stm32wlex))]
-    set_resume_config(config);
-
     // Switch to MSI to prevent problems with PLL configuration.
     if !RCC.cr().read().msion() {
         // Turn on MSI and configure it to 4MHz.
diff --git a/embassy-stm32/src/rcc/mod.rs b/embassy-stm32/src/rcc/mod.rs
index ca7c28cbc..66ee06e17 100644
--- a/embassy-stm32/src/rcc/mod.rs
+++ b/embassy-stm32/src/rcc/mod.rs
@@ -49,6 +49,9 @@ pub(crate) static mut REFCOUNT_STOP1: u32 = 0;
 /// May be read without a critical section
 pub(crate) static mut REFCOUNT_STOP2: u32 = 0;
 
+#[cfg(feature = "low-power")]
+pub(crate) static mut RCC_CONFIG: Option<Config> = None;
+
 #[cfg(backup_sram)]
 pub(crate) static mut BKSRAM_RETAINED: bool = false;
 
@@ -408,6 +411,7 @@ pub(crate) fn init_rcc(_cs: CriticalSection, config: Config) {
 
         #[cfg(feature = "low-power")]
         {
+            RCC_CONFIG = Some(config);
             REFCOUNT_STOP2 = 0;
             REFCOUNT_STOP1 = 0;
         }
diff --git a/embassy-stm32/src/rtc/mod.rs b/embassy-stm32/src/rtc/mod.rs
index 116b3c7ed..e88bd7ab2 100644
--- a/embassy-stm32/src/rtc/mod.rs
+++ b/embassy-stm32/src/rtc/mod.rs
@@ -379,13 +379,16 @@ trait SealedInstance {
 }
 
 #[cfg(feature = "low-power")]
-pub(crate) fn init_rtc(cs: CriticalSection, config: RtcConfig) {
+pub(crate) fn init_rtc(cs: CriticalSection, config: RtcConfig, min_stop_pause: embassy_time::Duration) {
+    use crate::time_driver::get_driver;
+
     #[cfg(feature = "_allow-disable-rtc")]
     if config._disable_rtc {
         return;
     }
 
-    crate::time_driver::get_driver().set_rtc(cs, Rtc::new_inner(config));
+    get_driver().set_rtc(cs, Rtc::new_inner(config));
+    get_driver().set_min_stop_pause(cs, min_stop_pause);
 
     trace!("low power: stop with rtc configured");
 }
diff --git a/embassy-stm32/src/time_driver.rs b/embassy-stm32/src/time_driver.rs
index 6d93b430a..0b75aef92 100644
--- a/embassy-stm32/src/time_driver.rs
+++ b/embassy-stm32/src/time_driver.rs
@@ -245,7 +245,7 @@ embassy_time_driver::time_driver_impl!(static DRIVER: RtcDriver = RtcDriver {
 impl RtcDriver {
     /// initialize the timer, but don't start it.  Used for chips like stm32wle5
     /// for low power where the timer config is lost in STOP2.
-    fn init_timer(&'static self, cs: critical_section::CriticalSection) {
+    pub(crate) fn init_timer(&'static self, cs: critical_section::CriticalSection) {
         let r = regs_gp16();
 
         rcc::enable_and_reset_with_cs::<T>(cs);
@@ -516,8 +516,3 @@ pub(crate) const fn get_driver() -> &'static RtcDriver {
 pub(crate) fn init(cs: CriticalSection) {
     DRIVER.init(cs)
 }
-
-#[cfg(all(feature = "low-power", stm32wlex))]
-pub(crate) fn init_timer(cs: CriticalSection) {
-    DRIVER.init_timer(cs)
-}
diff --git a/examples/stm32h5/src/bin/stop.rs b/examples/stm32h5/src/bin/stop.rs
index caebc9daf..8d5456b80 100644
--- a/examples/stm32h5/src/bin/stop.rs
+++ b/examples/stm32h5/src/bin/stop.rs
@@ -7,20 +7,12 @@
 use defmt::*;
 use embassy_executor::Spawner;
 use embassy_stm32::gpio::{AnyPin, Level, Output, Speed};
-use embassy_stm32::low_power::Executor;
 use embassy_stm32::rcc::{HSIPrescaler, LsConfig};
-use embassy_stm32::{Config, Peri};
+use embassy_stm32::{Config, Peri, low_power};
 use embassy_time::Timer;
 use {defmt_rtt as _, panic_probe as _};
 
-#[cortex_m_rt::entry]
-fn main() -> ! {
-    Executor::take().run(|spawner| {
-        spawner.spawn(unwrap!(async_main(spawner)));
-    })
-}
-
-#[embassy_executor::task]
+#[embassy_executor::main(executor = "low_power::Executor")]
 async fn async_main(spawner: Spawner) {
     defmt::info!("Program Start");
 
diff --git a/examples/stm32l5/src/bin/stop.rs b/examples/stm32l5/src/bin/stop.rs
index 3d119f90f..fde804fb7 100644
--- a/examples/stm32l5/src/bin/stop.rs
+++ b/examples/stm32l5/src/bin/stop.rs
@@ -4,20 +4,12 @@
 use defmt::*;
 use embassy_executor::Spawner;
 use embassy_stm32::gpio::{AnyPin, Level, Output, Speed};
-use embassy_stm32::low_power::Executor;
 use embassy_stm32::rcc::LsConfig;
-use embassy_stm32::{Config, Peri};
+use embassy_stm32::{Config, Peri, low_power};
 use embassy_time::Timer;
 use {defmt_rtt as _, panic_probe as _};
 
-#[cortex_m_rt::entry]
-fn main() -> ! {
-    Executor::take().run(|spawner| {
-        spawner.spawn(unwrap!(async_main(spawner)));
-    })
-}
-
-#[embassy_executor::task]
+#[embassy_executor::main(executor = "low_power::Executor")]
 async fn async_main(spawner: Spawner) {
     let mut config = Config::default();
     config.rcc.ls = LsConfig::default_lsi();
diff --git a/examples/stm32wle5/src/bin/adc.rs b/examples/stm32wle5/src/bin/adc.rs
index 4e0574d97..ea91fb063 100644
--- a/examples/stm32wle5/src/bin/adc.rs
+++ b/examples/stm32wle5/src/bin/adc.rs
@@ -6,20 +6,12 @@ use defmt::*;
 use defmt_rtt as _;
 use embassy_executor::Spawner;
 use embassy_stm32::adc::{Adc, SampleTime};
-use embassy_stm32::low_power::Executor;
+use embassy_stm32::low_power;
 use embassy_time::Timer;
 use panic_probe as _;
 use static_cell::StaticCell;
 
-#[cortex_m_rt::entry]
-fn main() -> ! {
-    info!("main: Starting!");
-    Executor::take().run(|spawner| {
-        spawner.spawn(unwrap!(async_main(spawner)));
-    });
-}
-
-#[embassy_executor::task]
+#[embassy_executor::main(executor = "low_power::Executor")]
 async fn async_main(_spawner: Spawner) {
     let mut config = embassy_stm32::Config::default();
     // enable HSI clock
diff --git a/examples/stm32wle5/src/bin/blinky.rs b/examples/stm32wle5/src/bin/blinky.rs
index b2745fdaf..9f0c04672 100644
--- a/examples/stm32wle5/src/bin/blinky.rs
+++ b/examples/stm32wle5/src/bin/blinky.rs
@@ -6,20 +6,12 @@ use defmt::*;
 use defmt_rtt as _;
 use embassy_executor::Spawner;
 use embassy_stm32::gpio::{Level, Output, Speed};
-use embassy_stm32::low_power::Executor;
+use embassy_stm32::low_power;
 use embassy_time::Timer;
 use panic_probe as _;
 use static_cell::StaticCell;
 
-#[cortex_m_rt::entry]
-fn main() -> ! {
-    info!("main: Starting!");
-    Executor::take().run(|spawner| {
-        spawner.spawn(unwrap!(async_main(spawner)));
-    });
-}
-
-#[embassy_executor::task]
+#[embassy_executor::main(executor = "low_power::Executor")]
 async fn async_main(_spawner: Spawner) {
     let mut config = embassy_stm32::Config::default();
     // enable HSI clock
diff --git a/examples/stm32wle5/src/bin/button_exti.rs b/examples/stm32wle5/src/bin/button_exti.rs
index db1bff0be..878eca7d0 100644
--- a/examples/stm32wle5/src/bin/button_exti.rs
+++ b/examples/stm32wle5/src/bin/button_exti.rs
@@ -7,19 +7,11 @@ use defmt_rtt as _;
 use embassy_executor::Spawner;
 use embassy_stm32::exti::ExtiInput;
 use embassy_stm32::gpio::Pull;
-use embassy_stm32::low_power::Executor;
+use embassy_stm32::low_power;
 use panic_probe as _;
 use static_cell::StaticCell;
 
-#[cortex_m_rt::entry]
-fn main() -> ! {
-    info!("main: Starting!");
-    Executor::take().run(|spawner| {
-        spawner.spawn(unwrap!(async_main(spawner)));
-    });
-}
-
-#[embassy_executor::task]
+#[embassy_executor::main(executor = "low_power::Executor")]
 async fn async_main(_spawner: Spawner) {
     let mut config = embassy_stm32::Config::default();
     // enable HSI clock
diff --git a/examples/stm32wle5/src/bin/i2c.rs b/examples/stm32wle5/src/bin/i2c.rs
index c31c673c9..68c17a672 100644
--- a/examples/stm32wle5/src/bin/i2c.rs
+++ b/examples/stm32wle5/src/bin/i2c.rs
@@ -6,9 +6,8 @@ use defmt::*;
 use defmt_rtt as _;
 use embassy_executor::Spawner;
 use embassy_stm32::i2c::I2c;
-use embassy_stm32::low_power::Executor;
 use embassy_stm32::time::Hertz;
-use embassy_stm32::{bind_interrupts, i2c, peripherals};
+use embassy_stm32::{bind_interrupts, i2c, low_power, peripherals};
 use embassy_time::{Duration, Timer};
 use panic_probe as _;
 use static_cell::StaticCell;
@@ -18,15 +17,7 @@ bind_interrupts!(struct IrqsI2C{
     I2C2_ER => i2c::ErrorInterruptHandler<peripherals::I2C2>;
 });
 
-#[cortex_m_rt::entry]
-fn main() -> ! {
-    info!("main: Starting!");
-    Executor::take().run(|spawner| {
-        spawner.spawn(unwrap!(async_main(spawner)));
-    });
-}
-
-#[embassy_executor::task]
+#[embassy_executor::main(executor = "low_power::Executor")]
 async fn async_main(_spawner: Spawner) {
     let mut config = embassy_stm32::Config::default();
     // enable HSI clock
diff --git a/tests/stm32/src/bin/stop.rs b/tests/stm32/src/bin/stop.rs
index 1fe65d867..83c375bc5 100644
--- a/tests/stm32/src/bin/stop.rs
+++ b/tests/stm32/src/bin/stop.rs
@@ -7,21 +7,13 @@ mod common;
 
 use chrono::NaiveDate;
 use common::*;
-use cortex_m_rt::entry;
 use embassy_executor::Spawner;
-use embassy_stm32::Config;
-use embassy_stm32::low_power::{Executor, StopMode, stop_ready};
+use embassy_stm32::low_power::{StopMode, stop_ready};
 use embassy_stm32::rcc::LsConfig;
 use embassy_stm32::rtc::Rtc;
+use embassy_stm32::{Config, low_power};
 use embassy_time::Timer;
 
-#[entry]
-fn main() -> ! {
-    Executor::take().run(|spawner| {
-        spawner.spawn(unwrap!(async_main(spawner)));
-    });
-}
-
 #[embassy_executor::task]
 async fn task_1() {
     for _ in 0..9 {
@@ -43,7 +35,7 @@ async fn task_2() {
     cortex_m::asm::bkpt();
 }
 
-#[embassy_executor::task]
+#[embassy_executor::main(executor = "low_power::Executor")]
 async fn async_main(spawner: Spawner) {
     let _ = config();