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Add Watchdog trait #13

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Add Watchdog trait #13

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a71a9c9
Trait to feed watchdog
williampMSFT Mar 9, 2026
8dcd438
send
williampMSFT Mar 9, 2026
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2 changes: 2 additions & 0 deletions embedded-mcu-hal/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,3 +5,5 @@ pub mod time;
/// Traits for NVRAM (Non-Volatile Random Access Memory) storage and management.
mod nvram;
pub use nvram::{Nvram, NvramStorage};

pub mod watchdog;
21 changes: 21 additions & 0 deletions embedded-mcu-hal/src/watchdog.rs
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@@ -0,0 +1,21 @@
//! Traits for interactions with a processor's watchdog timer.

/// Feeds an existing watchdog to ensure the processor isn't reset.
pub trait Watchdog: Send {
/// An enumeration of `Watchdog` errors.
///
type Error: core::fmt::Debug;

/// Restarts the countdown on the watchdog. This must be done once the watchdog is started
/// to prevent the processor being reset.
///
fn feed(&mut self) -> Result<(), Self::Error>;
}

impl<T: Watchdog> Watchdog for &mut T {
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@williampMSFT williampMSFT Mar 9, 2026 •
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This looked odd to my eye, but apparently this pattern was established in embedded-hal by rust-embedded/embedded-hal#310. I guess the idea is that this lets a function that takes an impl Watchdog as an argument be passed a &mut impl Watchdog and still work? It's not clear to me why you wouldn't just say that functions have to declare that their argument type is &mut impl Watchdog instead, but I think we want to align on what embedded-hal is doing, so I went with it. If anyone knows what the upside of doing this is I'd be interested in your take on it :)

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@kurtjd kurtjd Mar 10, 2026

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Yeah as we discussed offline, I think this pattern makes sense in some contexts/for some traits, but for a Watchdog specifically I can't think of a particular use case. Though I don't think it will necessarily hurt to have it here anyway as if someone really wants to pass an &mut impl Watchdog to a generic function there's nothing necessarily unsafe or problematic about that, since the compiler will just complain if they try to do anything funny.

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@kurtjd kurtjd Mar 10, 2026

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Though I do understand your concern that the blanket impl means a function that takes an impl Watchdog means we can't be certain if it will take an owned T or a &T and don't know if the watchdog will be dropped and thus disabled. I guess my thoughts are the user is responsible for understanding that (e.g. if they pass an owned watchdog they should understand it will be dropped).

type Error = T::Error;

fn feed(&mut self) -> Result<(), Self::Error> {
T::feed(self)
}
}