Enable RTC-based Time Alarm functionality by Ctru14 · Pull Request #542 · OpenDevicePartnership/embassy-imxrt

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)

Copilot

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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…docs, clear interrupts in handler

…ffset

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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

Copilot AI review requested due to automatic review settings January 13, 2026 22:59

Ctru14 requested a review from a team as a code owner January 13, 2026 22:59

Ctru14 requested review from RobertZ2011, gjpmsft, kurtjd and madeleyneVaca January 13, 2026 22:59

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fmt fixes

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williampMSFT reviewed Jan 13, 2026

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jerrysxie assigned felipebalbi Jan 13, 2026

jerrysxie added this to ODP Backlog Jan 13, 2026

Address Copilot PR feedback on set_alarm

11a3de9

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

Disable interrupt within critical section in clear_alarm

0d7a96e

Fix trailing whitespace

1407181

Copilot AI review requested due to automatic review settings January 13, 2026 23:19

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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…

2a8e309

…ffset

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Fix doc formatting

97bd30b

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register_alarm_waker added to hide the static AtomicWaker

d53cb80

williampMSFT previously approved these changes Jan 14, 2026

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felipebalbi reviewed Jan 14, 2026

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

628d09b

Copilot AI review requested due to automatic review settings January 14, 2026 22:13

Ctru14 dismissed williampMSFT’s stale review via 628d09b January 14, 2026 22:13

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

Clarify alarm documentation

1fda1f9

Disable 1Hz alarm bit in interrupt handler

3fc8ac9

Copilot AI review requested due to automatic review settings January 14, 2026 22:32

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DIsable RTC interrupt in alarm interrupt handler

7bef2e4

Ctru14 mentioned this pull request Jan 14, 2026

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

Closed

Remove Datetime conversions from set_alarm APIs

c307c04

Copilot AI review requested due to automatic review settings January 14, 2026 23:49

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Fix doc return type

a341e2b

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

williampMSFT approved these changes Jan 15, 2026

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Ctru14 closed this Jan 15, 2026

github-project-automation Bot moved this to Done in ODP Backlog Jan 15, 2026

Ctru14 reopened this Jan 15, 2026

felipebalbi merged commit fbf7df4 into OpenDevicePartnership:main Jan 15, 2026
22 checks passed

Ctru14 deleted the connortruono/rtc-alarm branch January 15, 2026 17:58

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Ctru14 commented Jan 13, 2026 •

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