3 files changed, 34 insertions, 22 deletions

diff --git a/embassy-nrf/src/time_driver.rs b/embassy-nrf/src/time_driver.rs
index 0d03ad529..bc2c8a3c1 100644
--- a/embassy-nrf/src/time_driver.rs
+++ b/embassy-nrf/src/time_driver.rs
@@ -245,19 +245,23 @@ impl Driver for RtcDriver {
 
     fn set_alarm(&self, alarm: AlarmHandle, timestamp: u64) -> bool {
         critical_section::with(|cs| {
-            let t = self.now();
-
-            // If alarm timestamp has passed don't set the alarm and return `false` to indicate that.
-            if timestamp <= t {
-                return false;
-            }
-
             let n = alarm.id() as _;
             let alarm = self.get_alarm(cs, alarm);
             alarm.timestamp.set(timestamp);
 
             let r = rtc();
 
+            let t = self.now();
+            if timestamp <= t {
+                // If alarm timestamp has passed the alarm will not fire.
+                // Disarm the alarm and return `false` to indicate that.
+                r.intenclr.write(|w| unsafe { w.bits(compare_n(n)) });
+
+                alarm.timestamp.set(u64::MAX);
+
+                return false;
+            }
+
             // If it hasn't triggered yet, setup it in the compare channel.
 
             // Write the CC value regardless of whether we're going to enable it now or not.
diff --git a/embassy-rp/src/timer.rs b/embassy-rp/src/timer.rs
index 8f280f550..80efd779f 100644
--- a/embassy-rp/src/timer.rs
+++ b/embassy-rp/src/timer.rs
@@ -71,13 +71,6 @@ impl Driver for TimerDriver {
     fn set_alarm(&self, alarm: AlarmHandle, timestamp: u64) -> bool {
         let n = alarm.id() as usize;
         critical_section::with(|cs| {
-            let now = self.now();
-
-            // If alarm timestamp has passed don't set the alarm and return `false` to indicate that.
-            if timestamp <= now {
-                return false;
-            }
-
             let alarm = &self.alarms.borrow(cs)[n];
             alarm.timestamp.set(timestamp);
 
@@ -87,7 +80,18 @@ impl Driver for TimerDriver {
             // it is checked if the alarm time has passed.
             unsafe { pac::TIMER.alarm(n).write_value(timestamp as u32) };
 
-            true
+            let now = self.now();
+            if timestamp <= now {
+                // If alarm timestamp has passed the alarm will not fire.
+                // Disarm the alarm and return `false` to indicate that.
+                unsafe { pac::TIMER.armed().write(|w| w.set_armed(1 << n)) }
+
+                alarm.timestamp.set(u64::MAX);
+
+                false
+            } else {
+                true
+            }
         })
     }
 }
diff --git a/embassy-stm32/src/time_driver.rs b/embassy-stm32/src/time_driver.rs
index e4c266e7f..ab55cc081 100644
--- a/embassy-stm32/src/time_driver.rs
+++ b/embassy-stm32/src/time_driver.rs
@@ -294,19 +294,23 @@ impl Driver for RtcDriver {
 
     fn set_alarm(&self, alarm: AlarmHandle, timestamp: u64) -> bool {
         critical_section::with(|cs| {
-            let t = self.now();
-
-            // If alarm timestamp has passed don't set the alarm and return `false` to indicate that.
-            if timestamp <= t {
-                return false;
-            }
-
             let r = T::regs_gp16();
 
             let n = alarm.id() as _;
             let alarm = self.get_alarm(cs, alarm);
             alarm.timestamp.set(timestamp);
 
+            let t = self.now();
+            if timestamp <= t {
+                // If alarm timestamp has passed the alarm will not fire.
+                // Disarm the alarm and return `false` to indicate that.
+                unsafe { r.dier().modify(|w| w.set_ccie(n + 1, false)) };
+
+                alarm.timestamp.set(u64::MAX);
+
+                return false;
+            }
+
             let safe_timestamp = timestamp.max(t + 3);
 
             // Write the CCR value regardless of whether we're going to enable it now or not.