Does not compile for target thumbv6em-none-eabi

[domtac]

Hello,

I am trying to add deluge to my cortex-m0 target using the thumbv6em-none-eabi toolchain.
Whereas I can compile everything easily with the thumbv7em-none-eabihf toolchain, the version 6 toolchain does give me the following error:

$ cargo build --target thumbv6em-none-eabi

   Compiling delog v0.1.6 (/Users/dominiktacke/Projects/rust/embedded/delog)
error[E0599]: no method named `fetch_add` found for reference `&'static AtomicUsize` in the current scope
   --> src/logger.rs:512:29
    |
512 |         delogger.attempts().fetch_add(1, Ordering::SeqCst);
    |                             ^^^^^^^^^ method not found in `&'static AtomicUsize`

error[E0599]: no method named `fetch_add` found for reference `&'static AtomicUsize` in the current scope
   --> src/logger.rs:519:34
    |
519 |             delogger.successes().fetch_add(1, Ordering::SeqCst);
    |                                  ^^^^^^^^^ method not found in `&'static AtomicUsize`

error[E0599]: no method named `compare_exchange` found for reference `&'static AtomicUsize` in the current scope
   --> src/logger.rs:538:47
    |
538 |             let previous = delogger.claimed().compare_exchange(
    |                                               ^^^^^^^^^^^^^^^^ method not found in `&'static AtomicUsize`

error[E0599]: no method named `fetch_add` found for reference `&'static AtomicUsize` in the current scope
   --> src/logger.rs:587:30
    |
587 |         delogger.successes().fetch_add(1, Ordering::SeqCst);
    |                              ^^^^^^^^^ method not found in `&'static AtomicUsize`

error[E0599]: no method named `fetch_add` found for reference `&'static AtomicUsize` in the current scope
   --> src/logger.rs:599:24
    |
599 |     delogger.flushes().fetch_add(1, Ordering::SeqCst);
    |                        ^^^^^^^^^ method not found in `&'static AtomicUsize`

For more information about this error, try `rustc --explain E0599`.
error: could not compile `delog` due to 5 previous errors

Tried this on a Mac M1 as well as in the rust:latest docker with the same result.

Ideas are highly appreciated

[elpiel]

As stated in the docs, these methods are only supported on platforms that support atomic operations on usize:

Note: This method is only available on platforms that support atomic operations on usize.

https://doc.rust-lang.org/stable/core/sync/atomic/struct.AtomicUsize.html#method.compare_exchange

One way to fix this would be to use https://docs.rs/atomic-polyfill/latest/atomic_polyfill/struct.AtomicUsize.html instead which also uses critical_section as dependency.
I don't see 6em supported but 6m is