Enable RTC-based Time Alarm functionality #542

Ctru14 · 2026-01-13T22:59:12Z

Enables access to the RTC alarm registers to provide an interrupt-based time alarm on the RTC peripheral. This allows for a lower power floor as the OsTimer can be shut down for longer periods in favor of an RTC wake.

Added the following to the RTC peripheral:

set_alarm() function
clear_alarm() function
RTC() interrupt handler on match
register_alarm_waker() function for use in Future::poll

rtc-alarm.rs demo added to RT685 EVK examples showing the custom RtcAlarm struct/Future needed to implement the alarm based on the consumer's peripheral synchronization

Demo results:

269.753145 [INFO ] RTC set time: Datetime { data: UncheckedDatetime { year: 2026, month: January, day: 12, hour: 16, minute: 0, second: 0, nanosecond: 0 } } (rtc_alarm src/bin/rtc-alarm.rs:56)
269.753381 [INFO ] Current time before alarm: Datetime { data: UncheckedDatetime { year: 2026, month: January, day: 12, hour: 16, minute: 0, second: 0, nanosecond: 0 } } (rtc_alarm src/bin/rtc-alarm.rs:61)
269.753466 [INFO ] Waiting 5 seconds... (rtc_alarm src/bin/rtc-alarm.rs:63)
274.753764 [INFO ] Current time after waiting: Datetime { data: UncheckedDatetime { year: 2026, month: January, day: 12, hour: 16, minute: 0, second: 4, nanosecond: 0 } } (rtc_alarm src/bin/rtc-alarm.rs:66)
274.753879 [INFO ] Setting alarm to trigger in 10 seconds... (rtc_alarm src/bin/rtc-alarm.rs:72)
274.754072 [INFO ] Waiting for alarm... (rtc_alarm src/bin/rtc-alarm.rs:81)
274.754231 [INFO ] Alarm pending at time Datetime { data: UncheckedDatetime { year: 2026, month: January, day: 12, hour: 16, minute: 0, second: 4, nanosecond: 0 } }, expires at 1768233614 (rtc_alarm src/bin/rtc-alarm.rs:26)
283.918927 [INFO ] Alarm triggered! Wake time: Datetime { data: UncheckedDatetime { year: 2026, month: January, day: 12, hour: 16, minute: 0, second: 14, nanosecond: 0 } } (rtc_alarm src/bin/rtc-alarm.rs:86)
283.919091 [INFO ] Alarm cleared (rtc_alarm src/bin/rtc-alarm.rs:90)

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Pull request overview

This PR enables RTC alarm functionality to allow interrupt-based time alarms, providing a lower power floor by allowing the OsTimer to be shut down in favor of RTC-based wakeups.

Changes:

Added set_alarm() and clear_alarm() methods to RtcDatetimeClock for configuring alarm interrupts
Implemented RTC interrupt handler to wake tasks when alarms fire
Added example demonstrating the alarm functionality with a custom Future implementation

Reviewed changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated 3 comments.

File	Description
src/rtc.rs	Added alarm functionality including set/clear methods, static waker, and interrupt handler
examples/rt685s-evk/src/bin/rtc-alarm.rs	New example demonstrating RTC alarm usage with custom Future implementation
examples/rt685s-evk/README.md	Updated documentation to use generic `[device]` placeholder

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src/rtc.rs

…docs, clear interrupts in handler

…ffset

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examples/rt685s-evk/src/bin/rtc-alarm.rs

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src/rtc.rs

Connor Truono added 2 commits January 13, 2026 11:01

Enable time alarm future and interrupt using the RTC peripheral

7e5e158

Move RtcAlarm structure out of RTC peripheral to user defined space

1b2e8af

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fmt fixes

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jerrysxie assigned felipebalbi Jan 13, 2026

jerrysxie added this to Embedded Controller Jan 13, 2026

Address Copilot PR feedback on set_alarm

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Connor Truono added 2 commits January 13, 2026 15:14

Disable interrupt within critical section in clear_alarm

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Fix trailing whitespace

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Connor Truono added 2 commits January 13, 2026 16:06

Ban access to static waker via function, mark methods as mut, update …

cb5e79d

…docs, clear interrupts in handler

Add separate APIs for setting the alarm at a time and at a relative o…

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…ffset

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Fix doc formatting

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register_alarm_waker added to hide the static AtomicWaker

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Address PR feedback on return types, critical section, and ordering

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Connor Truono added 2 commits January 14, 2026 14:21

Clarify alarm documentation

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Disable 1Hz alarm bit in interrupt handler

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DIsable RTC interrupt in alarm interrupt handler

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Ctru14 mentioned this pull request Jan 14, 2026

Datetime implementations for From and Into u64 OpenDevicePartnership/embedded-mcu#12

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Remove Datetime conversions from set_alarm APIs

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Fix doc return type

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felipebalbi approved these changes Jan 15, 2026

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This was referenced Jan 15, 2026

Enable multiple RTC time alarms to addresses set_alarm unsound potential #545

Open

RTC time alarm behavior of updating the time while a wait_from_now timer is active #546

Open

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Ctru14 closed this Jan 15, 2026

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Ctru14 reopened this Jan 15, 2026

felipebalbi merged commit fbf7df4 into OpenDevicePartnership:main Jan 15, 2026
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Ctru14 deleted the connortruono/rtc-alarm branch January 15, 2026 17:58

Enable RTC-based Time Alarm functionality #542

Enable RTC-based Time Alarm functionality #542

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Ctru14 commented Jan 13, 2026 •

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