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Merge pull request #3705 from embassy-rs/time-driver-fix

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Ensure alarm is re-scheduled if timetamp is in the past
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Dario Nieuwenhuis 2025-01-02 12:39:23 +00:00 committed by GitHub
commit eaa44c3d3f
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1 changed files with 45 additions and 38 deletions
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17
embassy-nrf/src/time_driver.rs
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@ -209,6 +209,7 @@ impl RtcDriver {
let r = rtc(); let r = rtc();
loop {
let t = self.now(); let t = self.now();
if timestamp <= t { if timestamp <= t {
// If alarm timestamp has passed the alarm will not fire. // If alarm timestamp has passed the alarm will not fire.
@ -230,9 +231,9 @@ impl RtcDriver {
// To workaround this, we never write a timestamp smaller than N+3. // To workaround this, we never write a timestamp smaller than N+3.
// N+2 is not safe because rtc can tick from N to N+1 between calling now() and writing cc. // N+2 is not safe because rtc can tick from N to N+1 between calling now() and writing cc.
// //
// It is impossible for rtc to tick more than once because // Since the critical section does not guarantee that a higher prio interrupt causes
// - this code takes less time than 1 tick // this to be delayed, we need to re-check how much time actually passed after setting the
// - it runs with interrupts disabled so nothing else can preempt it. // alarm, and retry if we are within the unsafe interval still.
// //
// This means that an alarm can be delayed for up to 2 ticks (from t+1 to t+3), but this is allowed // This means that an alarm can be delayed for up to 2 ticks (from t+1 to t+3), but this is allowed
// by the Alarm trait contract. What's not allowed is triggering alarms *before* their scheduled time, // by the Alarm trait contract. What's not allowed is triggering alarms *before* their scheduled time,
@ -243,13 +244,19 @@ impl RtcDriver {
let diff = timestamp - t; let diff = timestamp - t;
if diff < 0xc00000 { if diff < 0xc00000 {
r.intenset().write(|w| w.0 = compare_n(n)); r.intenset().write(|w| w.0 = compare_n(n));
// If we have not passed the timestamp, we can be sure the alarm will be invoked. Otherwise,
// we need to retry setting the alarm.
if self.now() + 2 <= timestamp {
return true;
}
} else { } else {
// If it's too far in the future, don't setup the compare channel yet. // If it's too far in the future, don't setup the compare channel yet.
// It will be setup later by `next_period`. // It will be setup later by `next_period`.
r.intenclr().write(|w| w.0 = compare_n(n)); r.intenclr().write(|w| w.0 = compare_n(n));
return true;
}
} }
true
} }
} }