embassy-time-driver using RTC interrupts #825

stillinbeta · 2025-03-11T02:42:06Z

Summary

These changes implement the embassy-time-driver interface, used by Embassy for scheduling and a prerequisite for the Embassy runtime.

These changes are confined to the embassy-time feature.

I have only tested these changes on the pyportal board (see examples provided).

Checklist

All new or modified code is well documented, especially public items
No new warnings or clippy suggestions have been introduced - CI will deny clippy warnings by default! You may #[allow] certain lints where reasonable, but ideally justify those with a short comment.

If Adding a new Board

Board CI added to crates.json
Board is properly following "Tier 2" conventions, unless otherwise decided to be "Tier 1"

If Adding a new cargo `feature` to the HAL

Feature is added to the test matrix for applicable boards / PACs in crates.json

Note

The crate changelogs should no longer be manually updated! Changelogs are now automatically generated. Instead:

If your PR is contained to a single crate, or a single feature:
- Nothing else to do; your PR will likely be squashed down to a single commit.
- Please consider using conventional commmit phrasing in the PR title.
If your PR brings in large, sweeping changes across multiple crates:
- Organize your commits such that each commit only touches a single crate, or a single feature across multiple crates. Please don't create commits that span multiple features over multiple crates.
- Use conventional commmits for your commit messages.

hal/src/rtc/mod.rs

stillinbeta · 2025-03-25T15:10:18Z

hal/src/rtc/embassy/mod.rs

+        if RtcMode0::check_interrupt_flag::<Compare0>(&rtc) {
+            // Due to synchronization delay, the RTC may be slightly behind
+            // Assume the current time is the time the interrupt is set for
+            let now = RtcMode0::get_compare(&rtc, 0) as u64;


@sjroe solved this by setting the prescaler to four, thus ensuring the resolution was coarse enough to not cause issues. I like my solution better, but am open to suggestions

update interrupt handling code close up modes Remove unneeded examples don't need semihosting remove rtt-target roll back config.toml

stillinbeta · 2025-03-27T02:47:00Z

boards/pyportal/examples/blinky_interrupt.rs

@@ -0,0 +1,163 @@
+//! Turn on and off with an LED


This could potentially be moved to another PR. I wrote this while debugging my interrupt code, and thought it might be a useful example for others in the future.

hal/src/rtc/modes.rs

jbeaurivage

Thanks for the PR @stillinbeta! I intend to review this shortly. In the meantime, could you revert these two changes? Thanks!

jbeaurivage · 2025-04-23T18:12:43Z

boards/pyportal/.cargo/config.toml

-runner = "hf2 elf"
-# runner = 'probe-rs run --chip ATSAMD51J20A'


Could you please revert this?

jbeaurivage · 2025-04-23T18:13:30Z

boards/pyportal/Cargo.toml

+# version = "0.21.0"
+path = "../../hal"


Same here, we'd like to keep pyportal a Tier 2 boarrd

Not sure exactly how to manage this, then. Should I have the PR to add embassy-time support be a stand-alone PR, then send another PR once there's a HAL release with the examples?

Yep, that would be the way to go! The second PR could already be opened, it's just a matter of timing of when we can merge it.

ritikmishra · 2025-06-08T10:14:05Z

hal/src/rtc/embassy.rs

+        let at = match u32::try_from(at) {
+            Ok(at) => at,
+            _ if at == u64::MAX => u32::MAX,
+            Err(_) => return false,
+        };
+
+        RtcMode0::set_compare(rtc, 0, at);
+        true


i am experiencing race condition in this implementation where it is possible for the RTC counter to advance past at while COMP0 is being set

the [embassy timer queue implementation for stm32 microcontrollers] tries to prevent this from happening by avoiding setting alarms for timestamps in the very near future:

…some minor changes made for the embassy time driver (see PR atsamd-rs#825).

kyp44 · 2025-06-14T02:26:06Z

As I'm interested in this getting merged, I had a good look at at and tested it. Here are some comments/questions:

The implementation is well done, and I appreciate that it utilizes the RTC modes abstraction layer instead of accessing the registers directly.
I tested this both on a Metro M0 (SAMD21G) and the PyGamer (SAMD51J) and it works really well.
For safety reasons, it seems like the driver init function should require the pac::Rtc as not doing so allows the user to simultaneously use the Rtc, which would be bad. Doing so would also allow init to not need to be unsafe. Is there particular a reason why this was not done?
init requires proof of the RTC clock being configured (e.g. RtcClock for thumbv6m chips), there are a couple of concerns with this:
a. For thumbv7 chips, this requires v2 of the clock API, which is not well support yet throughout the rest of the HAL, making it difficult to actually use for most projects. Perhaps an alternative init function could be added (and later removed after full migration) that does not require proof so as to be compatible with v1 on thumbv7 chips. Edit: Issue clock::v2 API migration discussion and tracking #912 tracks the progress of the clock v2 API migration.
b. This allows the user to configure the RTC clock to be whatever clock rate they like. However, embassy will always assume that the rate is 32.768 kHz due to passing the tick-hz-32_768 flag to embassy-time-drive. Unfortunately, unlike RTIC, it seems like the only way to specify the time driver tick rate is via these feature flags. We could just allow the user to set this flag themselves in their embassy-time dependency, but, annoyingly, this defaults to 1 MHz if nothing is specified, which will result in odd problems if the user is not aware they need to pass this themselves. An alternative would to for the driver to initialize the Rtc clock itself, always to the same rate, but this does not really seem possible to do for thumbv6 chips in a way that avoids at best a runtime panic. I believe with v2 (thumbv7 targets only right now) this could be done with compile-time assurances by simply passing in the RTC clock token.
As the embassy time counter is inherently a u64 while the RTC only supports u32, it would be good to enhance this with half-period counting (HPC) as the RTIC monotonic uses, otherwise tasks could stall around the 36-hour mark. This is an enhancement that could be added later that would not affect the API at all. The correct way to do this would probably be a single abstraction that incorporates HPC and can be used by both the embassy time driver and the RTIC monotonic. This is something I am certainly willing to take a crack at after this gets merged.

Note: This PR makes a few changes to the RTC modes abstraction. I also made some changes and additions with my RTC fixes in PR #845. In that PR I've already merged the changes from this one, so that version should take precedence in the event of any conflicts.

Edit: For my own purposes, I'm maintaining this branch in my fork that I am keeping up to date with atsamd-rs/atsamd:master (via rebasing) and have correctly merged in the changes from PR #845 discussed above. Since this is rebased, I don't know that a PR against stillinbeta/atsamd:embassy-interrupt would work correctly.

…some minor changes made for the embassy time driver (see PR atsamd-rs#825).

stillinbeta force-pushed the embassy-interrupt branch from d853b9d to 85a1edf Compare March 11, 2025 02:47

stillinbeta commented Mar 11, 2025

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hal/src/rtc/mod.rs Outdated Show resolved Hide resolved

stillinbeta force-pushed the embassy-interrupt branch from b046fc1 to 651dd87 Compare March 25, 2025 14:44

stillinbeta commented Mar 25, 2025

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stillinbeta force-pushed the embassy-interrupt branch 2 times, most recently from 6247d9a to 9182bd0 Compare March 27, 2025 02:34

stillinbeta added 9 commits March 26, 2025 19:42

it works don't touch anything

56d4df1

blinky interrupt

d96518b

Working embassy-interrupt implementation (for at least one board)

1c74c91

update interrupt handling code close up modes Remove unneeded examples don't need semihosting remove rtt-target roll back config.toml

fmt and cleanup

aeadd82

fix blinky interrupt example

0688717

cargo fmt (with line wrapping now)

f63fcd7

Fmt and moving stuff

8107d35

comments and lints

f4e131b

Move initialising the embassy driver to a macro

f2af62e

stillinbeta force-pushed the embassy-interrupt branch from 9182bd0 to f2af62e Compare March 27, 2025 02:42

stillinbeta marked this pull request as ready for review March 27, 2025 02:42

stillinbeta commented Mar 27, 2025

View reviewed changes

hal/src/rtc/modes.rs Outdated Show resolved Hide resolved

Comments and tidying for rtc modes

836de18

stillinbeta marked this pull request as draft March 27, 2025 03:46

stillinbeta changed the title ~~(wip) embassy-time-driver using RTC interrupts~~ embassy-time-driver using RTC interrupts Mar 27, 2025

stillinbeta force-pushed the embassy-interrupt branch from 8126267 to 2ccaefe Compare March 27, 2025 03:49

stillinbeta added 2 commits March 26, 2025 20:57

Add embassy-time to crates.json

4645859

Require a token of rtc configuration

a78cb55

stillinbeta force-pushed the embassy-interrupt branch from 2ccaefe to a78cb55 Compare March 28, 2025 01:54

stillinbeta added 2 commits March 27, 2025 19:12

lints and fmt

c813b1c

Remove sync_wait!

3d7a961

stillinbeta force-pushed the embassy-interrupt branch from 1a81ae9 to 3d7a961 Compare March 28, 2025 02:43

stillinbeta marked this pull request as ready for review March 28, 2025 02:47

jbeaurivage requested changes Apr 23, 2025

View reviewed changes

ritikmishra added a commit to ritikmishra/atsamd that referenced this pull request Jun 4, 2025

squash atsamd-rs#825

c0e3159

ritikmishra reviewed Jun 8, 2025

View reviewed changes

kyp44 added a commit to kyp44/atsamd that referenced this pull request Jun 13, 2025

feat(rtc): Further tweaks made to the RTC modes abstraction, merging …

8f3c80b

…some minor changes made for the embassy time driver (see PR atsamd-rs#825).

kyp44 added a commit to kyp44/atsamd that referenced this pull request Jun 13, 2025

feat(rtc): Further tweaks made to the RTC modes abstraction, merging …

dbb700b

…some minor changes made for the embassy time driver (see PR atsamd-rs#825).

kyp44 added a commit to kyp44/atsamd that referenced this pull request Jun 18, 2025

feat(rtc): Further tweaks made to the RTC modes abstraction, merging …

36eb91c

…some minor changes made for the embassy time driver (see PR atsamd-rs#825).

kyp44 added a commit to kyp44/atsamd that referenced this pull request Jun 20, 2025

feat(rtc): Further tweaks made to the RTC modes abstraction, merging …

2ad09d8

…some minor changes made for the embassy time driver (see PR atsamd-rs#825).

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stillinbeta commented Mar 11, 2025 •

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		runner = "hf2 elf"
		# runner = 'probe-rs run --chip ATSAMD51J20A'

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Summary

Checklist

If Adding a new Board

If Adding a new cargo feature to the HAL

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