stm32: fix rtc wakeup timing and add dbg

embassy-stm32/Cargo.toml

@@ -8,7 +8,7 @@ license = "MIT OR Apache-2.0"
 src_base = "https://github.com/embassy-rs/embassy/blob/embassy-stm32-v$VERSION/embassy-stm32/src/"
 src_base_git = "https://github.com/embassy-rs/embassy/blob/$COMMIT/embassy-stm32/src/"
 
-features = ["nightly", "defmt", "unstable-pac", "unstable-traits", "exti", "time-driver-any", "time", "low-power"]
+features = ["nightly", "defmt", "unstable-pac", "unstable-traits", "exti", "time-driver-any", "time", "low-power", "rtc-debug"]
 flavors = [
     { regex_feature = "stm32f0.*", target = "thumbv6m-none-eabi" },
     { regex_feature = "stm32f1.*", target = "thumbv7m-none-eabi" },
@@ -90,6 +90,7 @@ defmt = ["dep:defmt", "bxcan/unstable-defmt", "embassy-sync/defmt", "embassy-emb
 
 exti = []
 low-power = [ "dep:embassy-executor", "embassy-executor/arch-cortex-m" ]
+rtc-debug = []
 embassy-executor = []
 
 ## Automatically generate `memory.x` file using [`stm32-metapac`](https://docs.rs/stm32-metapac/)

embassy-stm32/src/low_power.rs

@@ -89,6 +89,9 @@ impl Executor {
 
         self.time_driver.resume_time();
         trace!("low power: resume time");
+
+        #[cfg(feature = "rtc-debug")]
+        cortex_m::asm::bkpt();
     }
 
     pub(self) fn stop_with_rtc(&mut self, rtc: &'static Rtc) {
@@ -118,6 +121,7 @@ impl Executor {
         }
 
         trace!("low power: enter stop...");
+        #[cfg(not(feature = "rtc-debug"))]
         self.scb.set_sleepdeep();
     }
 
@@ -140,6 +144,9 @@ impl Executor {
     ///
     /// This function never returns.
     pub fn run(&'static mut self, init: impl FnOnce(Spawner)) -> ! {
+        #[cfg(feature = "rtc-debug")]
+        trace!("low power: rtc debug enabled");
+
         init(unsafe { EXECUTOR.as_mut().unwrap() }.inner.spawner());
 
         loop {

embassy-stm32/src/rcc/f4.rs

@@ -17,7 +17,7 @@ use crate::{peripherals, Peripheral};
 pub const HSI_FREQ: Hertz = Hertz(16_000_000);
 
 /// LSI speed
-pub const LSI_FREQ: Hertz = Hertz(32_000);
+pub const LSI_FREQ: Hertz = Hertz(32_768);
 
 /// Clocks configuration
 #[non_exhaustive]

embassy-stm32/src/rtc/mod.rs

@@ -47,6 +47,18 @@ struct RtcInstant {
     subsecond: u16,
 }
 
+#[cfg(all(feature = "low-power", feature = "defmt"))]
+impl defmt::Format for RtcInstant {
+    fn format(&self, fmt: defmt::Formatter) {
+        defmt::write!(
+            fmt,
+            "{}:{}",
+            self.second,
+            RTC::regs().prer().read().prediv_s() - self.subsecond,
+        )
+    }
+}
+
 #[cfg(feature = "low-power")]
 impl core::ops::Sub for RtcInstant {
     type Output = embassy_time::Duration;
@@ -174,7 +186,7 @@ impl Rtc {
         let second = bcd2_to_byte((tr.st(), tr.su()));
 
         // Unlock the registers
-        r.dr();
+        r.dr().read();
 
         RtcInstant { second, subsecond }
     }

embassy-stm32/src/rtc/v2.rs

@@ -1,7 +1,5 @@
 use stm32_metapac::rtc::vals::{Init, Osel, Pol};
 
-#[cfg(feature = "low-power")]
-use super::RtcInstant;
 use super::{sealed, RtcConfig};
 use crate::pac::rtc::Rtc;
 use crate::peripherals::RTC;
@@ -77,6 +75,21 @@ impl super::Rtc {
     /// start the wakeup alarm and wtih a duration that is as close to but less than
     /// the requested duration, and record the instant the wakeup alarm was started
     pub(crate) fn start_wakeup_alarm(&self, requested_duration: embassy_time::Duration) {
+        #[cfg(feature = "rtc-debug")]
+        if critical_section::with(|cs| {
+            if let Some(instant) = self.stop_time.borrow(cs).take() {
+                self.stop_time.borrow(cs).replace(Some(instant));
+
+                Some(())
+            } else {
+                None
+            }
+        })
+        .is_some()
+        {
+            return;
+        }
+
         use embassy_time::{Duration, TICK_HZ};
 
         use crate::rcc::get_freqs;
@@ -86,17 +99,14 @@ impl super::Rtc {
         let rtc_ticks = requested_duration.as_ticks() * rtc_hz / TICK_HZ;
         let prescaler = WakeupPrescaler::compute_min((rtc_ticks / u16::MAX as u64) as u32);
 
-        // adjust the rtc ticks to the prescaler
+        // adjust the rtc ticks to the prescaler and subtract one rtc tick
         let rtc_ticks = rtc_ticks / (<WakeupPrescaler as Into<u32>>::into(prescaler) as u64);
         let rtc_ticks = if rtc_ticks >= u16::MAX as u64 {
             u16::MAX - 1
         } else {
             rtc_ticks as u16
-        };
-
-        let duration = Duration::from_ticks(
-            rtc_ticks as u64 * TICK_HZ * (<WakeupPrescaler as Into<u32>>::into(prescaler) as u64) / rtc_hz,
-        );
+        }
+        .saturating_sub(1);
 
         self.write(false, |regs| {
             regs.cr().modify(|w| w.set_wute(false));
@@ -104,11 +114,21 @@ impl super::Rtc {
             while !regs.isr().read().wutwf() {}
 
             regs.cr().modify(|w| w.set_wucksel(prescaler.into()));
+            regs.wutr().write(|w| w.set_wut(rtc_ticks));
             regs.cr().modify(|w| w.set_wute(true));
             regs.cr().modify(|w| w.set_wutie(true));
         });
 
-        trace!("rtc: start wakeup alarm for {} ms", duration.as_millis());
+        trace!(
+            "rtc: start wakeup alarm for {} ms (psc: {}, ticks: {}) at {}",
+            Duration::from_ticks(
+                rtc_ticks as u64 * TICK_HZ * (<WakeupPrescaler as Into<u32>>::into(prescaler) as u64) / rtc_hz,
+            )
+            .as_millis(),
+            <WakeupPrescaler as Into<u32>>::into(prescaler),
+            rtc_ticks,
+            self.instant(),
+        );
 
         critical_section::with(|cs| assert!(self.stop_time.borrow(cs).replace(Some(self.instant())).is_none()))
     }
@@ -119,7 +139,10 @@ impl super::Rtc {
     pub(crate) fn stop_wakeup_alarm(&self) -> Option<embassy_time::Duration> {
         use crate::interrupt::typelevel::Interrupt;
 
-        trace!("rtc: stop wakeup alarm...");
+        trace!("rtc: stop wakeup alarm at {}", self.instant());
+
+        #[cfg(feature = "rtc-debug")]
+        return None;
 
         self.write(false, |regs| {
             regs.cr().modify(|w| w.set_wutie(false));

embassy-stm32/src/time_driver.rs

@@ -363,6 +363,7 @@ impl RtcDriver {
                     .start_wakeup_alarm(time_until_next_alarm);
             });
 
+            #[cfg(not(feature = "rtc-debug"))]
             T::regs_gp16().cr1().modify(|w| w.set_cen(false));
 
             Ok(())
@@ -374,6 +375,7 @@ impl RtcDriver {
     pub(crate) fn resume_time(&self) {
         self.stop_wakeup_alarm();
 
+        #[cfg(not(feature = "rtc-debug"))]
         T::regs_gp16().cr1().modify(|w| w.set_cen(true));
     }
 }

tests/stm32/src/bin/stop.rs

@@ -46,8 +46,10 @@ async fn async_main(_spawner: Spawner) {
 
     stop_with_rtc(rtc);
 
-    info!("Waiting 5 seconds");
-    Timer::after(Duration::from_secs(5)).await;
+    info!("Waiting...");
+    Timer::after(Duration::from_secs(2)).await;
+    info!("Waiting...");
+    Timer::after(Duration::from_secs(3)).await;
 
     info!("Test OK");
     cortex_m::asm::bkpt();