Does the SPSC implementation really need portable atomics / cas?

[MarcusGrass]

Hi,

I made a somewhat broken migration of a non-thread-safe SPSC to a thread-safe one looking at the SPSC implementation here for guidance.

I came over this part of the docs

This module requires CAS atomic instructions which are not available on all architectures
(e.g. ARMv6-M (thumbv6m-none-eabi) and MSP430 (msp430-none-elf)). These atomics can be
emulated however with portable-atomic, which is
enabled with the cas feature and is enabled by default for thumbv6m-none-eabi and riscv32
targets.

But the implementation doesn't seem to use any CAS-instructions at all.

I'm not that familiar with embedded so maybe there's something I'm missing here, does the SPSC really need portable_atomic (if #[cfg(target_has_atomic_load_store = "ptr")], important caveat`, shouldn't be necessary if the target has atomic load store).