AVR examples?

[MarkuBu]

I noticed that AVR support is listed in the official documentation

https://docs.embassy.dev/embassy-executor/git/std/index.html#architecture

How far has AVR support progressed? Are there any examples, e.g. for an Arduino Uno?

All I found is this https://github.com/niclashoyer/embassy-avr-blink

Has there been any progress since then?

[lulf]

The only thing that have been added for AVR is support in the embassy-executor. AFAIK no one is actively working on AVR support.

There is no HAL inside embassy, but you might be able to pick a HAL from another crate on crates.io (I can see some atmega PAC and HALs there). There is also a PR here #3696 for adding an example.

[brainstorm]

Well, I have this toy example: https://github.com/brainstorm/embassy-as5600/

And it worked well on Espressif ICs around a year ago, but for AVR I was facing some challenges (panics). Fast forward to today, it does not seem to even compile (it 100% compiled at least back then!):

% rustc --version
rustc 1.87.0-nightly (f04bbc60f 2025-02-20)

% cargo build
(...)
error[E0432]: unresolved import `core::sync::atomic::AtomicPtr`
   --> /Users/rvalls/.cargo/git/checkouts/embassy-c08a80187403f815/0edd45e/embassy-executor/src/raw/mod.rs:31:26
    |
31  | use core::sync::atomic::{AtomicPtr, Ordering};
    |                          ^^^^^^^^^
    |                          |
    |                          no `AtomicPtr` in `sync::atomic`
    |                          help: a similar name exists in the module: `AtomicI8`
    |
    = help: consider importing this struct instead:
            portable_atomic::AtomicPtr
note: found an item that was configured out
   --> /Users/rvalls/.rustup/toolchains/nightly-aarch64-apple-darwin/lib/rustlib/src/rust/library/core/src/sync/atomic.rs:301:12
    |
301 | pub struct AtomicPtr<T> {
    |            ^^^^^^^^^
note: the item is gated behind the `ptr` feature
   --> /Users/rvalls/.rustup/toolchains/nightly-aarch64-apple-darwin/lib/rustlib/src/rust/library/core/src/sync/atomic.rs:295:7
    |
295 | #[cfg(target_has_atomic_load_store = "ptr")]
    |       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

For more information about this error, try `rustc --explain E0432`.
error: could not compile `embassy-executor` (lib) due to 1 previous error
warning: build failed, waiting for other jobs to finish...

/cc @Autofix

[brainstorm]

There are more recent (and seemingly working examples) too over here: https://github.com/simmsb/tyrfing (by @simmsb who seems to be using his own embassy fork?).

[simmsb]

who seems to be using his own embassy fork?

Yeah, I found that 64 bit time caused a significant amount of code to be generated, switching out to a 32 bit reduced code size by quite a bit. Though perhaps there are other ways to prevent to 8 byte load/add/store instruction sequences being inlined everywhere.

On that project I spent a fair amount of time micro-optimising code size, I'll try to remember everything I did:

1. Swapping the embassy timer to a 32 bit
2. Removing the 'don't replace waker if both wake the same task' check here.
3. Using turbowakers (these save quite a lot of code size on AVR)
4. Reducing the number of different future types in use (e.g. by only using future combinators with dyn Future)
5. Preventing inlining of larger async fn futures, as generated future size seems to scale nonlinear with the number of states.