stm32/lp: add refcount

embassy-stm32/build.rs

@@ -356,6 +356,8 @@ fn main() {
                     }
                     fn enable() {
                         critical_section::with(|_| {
+                            #[cfg(feature = "low-power")]
+                            crate::rcc::clock_refcount_add();
                             crate::pac::RCC.#en_reg().modify(|w| w.#set_en_field(true));
                             #after_enable
                         })
@@ -363,6 +365,8 @@ fn main() {
                     fn disable() {
                         critical_section::with(|_| {
                             crate::pac::RCC.#en_reg().modify(|w| w.#set_en_field(false));
+                            #[cfg(feature = "low-power")]
+                            crate::rcc::clock_refcount_sub();
                         })
                     }
                     fn reset() {

embassy-stm32/src/rcc/mod.rs

@@ -26,6 +26,8 @@ use crate::time::Hertz;
 #[cfg_attr(any(rcc_h5, rcc_h50), path = "h5.rs")]
 mod _version;
 pub use _version::*;
+#[cfg(feature = "low-power")]
+use atomic_polyfill::{AtomicU32, Ordering};
 
 #[derive(Clone, Copy, Debug)]
 #[cfg_attr(feature = "defmt", derive(defmt::Format))]
@@ -79,6 +81,25 @@ pub struct Clocks {
     pub rtc: Option<Hertz>,
 }
 
+#[cfg(feature = "low-power")]
+static CLOCK_REFCOUNT: AtomicU32 = AtomicU32::new(0);
+
+#[cfg(feature = "low-power")]
+pub fn low_power_ready() -> bool {
+    CLOCK_REFCOUNT.load(Ordering::SeqCst) == 0
+}
+
+#[cfg(feature = "low-power")]
+pub(crate) fn clock_refcount_add() {
+    // We don't check for overflow because constructing more than u32 peripherals is unlikely
+    CLOCK_REFCOUNT.fetch_add(1, Ordering::Relaxed);
+}
+
+#[cfg(feature = "low-power")]
+pub(crate) fn clock_refcount_sub() {
+    assert!(CLOCK_REFCOUNT.fetch_sub(1, Ordering::Relaxed) != 0);
+}
+
 /// Frozen clock frequencies
 ///
 /// The existence of this value indicates that the clock configuration can no longer be changed