differentiate full vs CAS polyfill

build.rs

@@ -52,10 +52,16 @@ fn main() -> Result<(), Box<dyn Error>> {
         }
     };
 
-    // Let the code know if it should use atomic-polyfill or not
+    // Let the code know if it should use atomic-polyfill or not, and what aspects
+    // of polyfill it requires
     match &target[..] {
-        "thumbv6m-none-eabi" | "riscv32i-unknown-none-elf" | "riscv32imc-unknown-none-elf" => {
-            println!("cargo:rustc-cfg=use_atomic_polyfill");
+        "riscv32i-unknown-none-elf" | "riscv32imc-unknown-none-elf" => {
+            println!("cargo:rustc-cfg=full_atomic_polyfill");
+            println!("cargo:rustc-cfg=cas_atomic_polyfill");
+        }
+
+        "thumbv6m-none-eabi" => {
+            println!("cargo:rustc-cfg=cas_atomic_polyfill");
         }
         _ => {}
     }

src/mpmc.rs

@@ -87,18 +87,18 @@
 
 use core::{cell::UnsafeCell, mem::MaybeUninit};
 
-#[cfg(all(feature = "mpmc_large", not(use_atomic_polyfill)))]
+#[cfg(all(feature = "mpmc_large", not(cas_atomic_polyfill)))]
 type AtomicTargetSize = core::sync::atomic::AtomicUsize;
-#[cfg(all(feature = "mpmc_large", use_atomic_polyfill))]
+#[cfg(all(feature = "mpmc_large", cas_atomic_polyfill))]
 type AtomicTargetSize = atomic_polyfill::AtomicUsize;
-#[cfg(all(not(feature = "mpmc_large"), not(use_atomic_polyfill)))]
+#[cfg(all(not(feature = "mpmc_large"), not(cas_atomic_polyfill)))]
 type AtomicTargetSize = core::sync::atomic::AtomicU8;
-#[cfg(all(not(feature = "mpmc_large"), use_atomic_polyfill))]
+#[cfg(all(not(feature = "mpmc_large"), cas_atomic_polyfill))]
 type AtomicTargetSize = atomic_polyfill::AtomicU8;
 
-#[cfg(not(use_atomic_polyfill))]
+#[cfg(not(cas_atomic_polyfill))]
 type Ordering = core::sync::atomic::Ordering;
-#[cfg(use_atomic_polyfill)]
+#[cfg(cas_atomic_polyfill)]
 type Ordering = atomic_polyfill::Ordering;
 
 #[cfg(feature = "mpmc_large")]

src/pool/llsc.rs

@@ -3,10 +3,10 @@
 pub use core::ptr::NonNull as Ptr;
 use core::{cell::UnsafeCell, ptr};
 
-#[cfg(use_atomic_polyfill)]
+#[cfg(cas_atomic_polyfill)]
 use atomic_polyfill::{AtomicPtr, Ordering};
 
-#[cfg(not(use_atomic_polyfill))]
+#[cfg(not(cas_atomic_polyfill))]
 use core::sync::atomic::{AtomicPtr, Ordering};
 
 /// Unfortunate implementation detail required to use the

src/pool/singleton/arc.rs

@@ -81,10 +81,10 @@ use core::{
     sync::atomic,
 };
 
-#[cfg(use_atomic_polyfill)]
+#[cfg(cas_atomic_polyfill)]
 use atomic_polyfill::{AtomicUsize, Ordering};
 
-#[cfg(not(use_atomic_polyfill))]
+#[cfg(not(cas_atomic_polyfill))]
 use core::sync::atomic::{AtomicUsize, Ordering};
 
 use crate::pool::{self, stack::Ptr, Node};

src/spsc.rs

@@ -2,8 +2,8 @@
 //!
 //! Implementation based on <https://www.codeproject.com/Articles/43510/Lock-Free-Single-Producer-Single-Consumer-Circular>
 //!
-//! NOTE: This module is not available on targets that do *not* support atomic loads, e.g. RISC-V
-//! cores w/o the A (Atomic) extension
+//! NOTE: This module is not available on targets that do *not* support atomic loads and are not
+//! supported by [`atomic_polyfill`]. (e.g., MSP430).
 //!
 //! # Examples
 //!
@@ -84,13 +84,12 @@
 //! - The numbers reported correspond to the successful path (i.e. `Some` is returned by `dequeue`
 //! and `Ok` is returned by `enqueue`).
 
-use core::{
-    cell::UnsafeCell,
-    fmt, hash,
-    mem::MaybeUninit,
-    ptr,
-    sync::atomic::{AtomicUsize, Ordering},
-};
+use core::{cell::UnsafeCell, fmt, hash, mem::MaybeUninit, ptr};
+
+#[cfg(full_atomic_polyfill)]
+use atomic_polyfill::{AtomicUsize, Ordering};
+#[cfg(not(full_atomic_polyfill))]
+use core::sync::atomic::{AtomicUsize, Ordering};
 
 /// A statically allocated single producer single consumer queue with a capacity of `N - 1` elements
 ///