Q: How to use Wait::wait_for_low and avoid the race condition between interrupt setup and pin triggering?

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Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
25/100
Issue type
Documentation
Clarity
Needs clarification
Activity status
Stale
Tech stack
rust
Domain
embedded-iot

Research direction

Start with embedded-hal-async/src/digital.rs at the Wait trait and compare the esp-hal GPIO implementation linked in the report. Determine whether the trait needs usage guidance or an API change to make interrupt setup safe before triggering activity, then document or specify the intended sequence and its completion criteria.

Written by the indexing model from the issue text.

Description

Hi folks,

I am trying to detect a brief pulse using embedded-hal-async GPIO Wait trait. The methods like wait_for_low are perfect for that in general (https://github.com/rust-embedded/embedded-hal/blob/master/embedded-hal-async/src/digital.rs#L34)

However most of the implementations I have seen configure the interrupt within the wait_for_low method which means it must first be polled at least once (but sometimes more) before the interrupt is set up properly. See for example how the esp waits for the setup to be possible here https://github.com/esp-rs/esp-hal/blob/87d501766f178a2dd812c382ca257d268ee266ad/esp-hal/src/gpio/mod.rs#L2242

Now, I have a device where the pulse can disappear on its own and I need to detect it reliably. I have custom code that first sets up the interrupt and only then triggers the behavior. This works, but I would like to rewrite my custom code to adhere to the embedded-hal-async traits.

Do you have any idea about how to use the wait_for_low in this way? First set-up the interrupts, then do something outside to trigger the activity and then wait for the interrupt to happen?

The code I have right know looks roughly like this:

let w = WaitForPin::listen(gpio, pin, LOW);
device.start()
w.await;

TLDR: How to use Wait::wait_for_low and avoid the race condition between interrupt setup and pin triggering?

Dominant language
Rust
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