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nrf/rtc: fix race when setting alarms too close to now.

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This commit is contained in:
Dario Nieuwenhuis 2021-01-13 03:17:58 +01:00
parent 5229a1991c
commit 6963b314a2
1 changed files with 6 additions and 11 deletions
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17
embassy-nrf/src/rtc.rs
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@ -182,18 +182,13 @@ impl<T: Instance> RTC<T> {
let diff = timestamp - t;
if diff < 0xc00000 {
self.rtc.cc[n].write(|w| unsafe { w.bits(timestamp as u32 & 0xFFFFFF) });
// nrf52 docs say:
// If the COUNTER is N, writing N or N+1 to a CC register may not trigger a COMPARE event.
// 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.
let safe_timestamp = timestamp.max(t + 3);
self.rtc.cc[n].write(|w| unsafe { w.bits(safe_timestamp as u32 & 0xFFFFFF) });
self.rtc.intenset.write(|w| unsafe { w.bits(compare_n(n)) });
// We may have been preempted for arbitrary time between checking if `at` is in the past
// and setting the cc. In that case, we don't know if the cc has triggered.
// So, we check again just in case.
let t = self.now();
if timestamp <= t {
self.trigger_alarm(n, cs);
return;
}
} else {
self.rtc.intenclr.write(|w| unsafe { w.bits(compare_n(n)) });
}