Compatibility with ATMEGA architecture

[chuckberrypi]

The docs say that this project maintains hal crates for various architectures (RP2040, STM, NRF), but that "you can still use HALs from other projects with Embassy." Does this mean that I can use embassy with an ATMEGA32u4 microcontroller I have, or can I only use it with the architectures listed on the embassy-executor documentation? If I can use it with the ATMEGA32u4 chip, any tips on getting rid of the error I am getting:

| #[embassy_executor::main]
|                     ^^^^ could not find \`main\` in \`embassy_executor\`

[enbyted]

Embassy-executor has some platform-dependent code required to support it, kind of like any embedded operating system.

Arguably it should not be very difficult to create a thread-mode (i.e. endless loop in main function) executor for AVR.

Regarding the error you're getting - the main macro is only defined if you select a valid architecture --> that's because it needs to know which platform-specific executor to use.

I'm not an embassy expert (just started using it a couple weeks ago on a toy project actually), but to me it looks like to add basic AVR support you'd need at least:

• Add executor implementation to embassy-executor/src/arch/ - look at the cortex_m implementation for reference. Probably skip the interrupt executor --> make it fail if enabled.
• Implement __pender in the same file
• Add the main macro support to embassy-executor-macros

The simplest executor you can make is one that will do:

pub fn run(&'static mut self, init: impl FnOnce(Spawner)) -> ! {
    init(self.inner.spawner());
    loop { unsafe {self.iner.pool(); } }
}

For testing you can just start with using embassy_executor::raw::Executor (docs)

I did not even try to compile below code (never tried rust on AVR), but you could try something along those lines:

use embassy_executor::raw;
use static_cell::StaticCell;

static EXECUTOR: raw::Executor = StaticCell::new();

#[export_name = "__pender"]
/// Required by raw::Executor, but can do nothing
fn pender(_context: *mut ()) {}

pub fn main()
{
  let executor = EXECUTOR.init(raw::Executor::new(ptr::null_mut()));
  let _spawner = executor.spawner();

  loop { 
    unsafe { executor.pool(); } 
  }
}

[jamesmunns]

Note that there is a PR open to add some support for AVR: https://github.com/embassy-rs/embassy/pull/2273