atomic-polyfill

• Update to critical-section v1.0

• Bump critical-section dependency from 0.2 to 1.0.

  This is a breaking change if you were relying on the default implementations available on critical-section 0.2.7 and earlier. They have been removed in critical-section 0.2.8 because they were unsound, since there's no way to guarantee they're correct for the target in use (for example for multi-core embedded targets). Since critical-section 0.2.8 just forwards to 1.0 now, we decided to change atomic-polyfill to use 1.0 directly.

  If you're seeing a linker error like undefined symbol: _critical_section_1_0_acquire, you're affected. To fix it:

  • If your target supports std: Add the critical-section dependency to Cargo.toml enabling the std feature.

    [dependencies]
    critical-section = { version = "1.1", features = ["std"]}
    

  • For single-core Cortex-M targets in privileged mode:

    [dependencies]
    cortex-m = { version = "0.7.6", features = ["critical-section-single-core"]}
    

  • For single-hart RISC-V targets in privileged mode:

    [dependencies]
    riscv = { version = "0.10", features = ["critical-section-single-hart"]}
    

  • For other targets: check if your HAL or architecture-support crate has a critical-section 1.0 implementation available. Otherwise, provide your own.

• Fix AtomicPtr accidentally not being available when not polyfilled.

• Switch to only two polyfill levels.

The "CAS" level which uses atomic load/store and critical-section based CAS was not sound, because critical-section guarantees only "no other critical section can run concurrently", not "no other code can run concurrently". Therefore a CS-based CAS can still race a native atomic store.

• Added AVR support.

• Added support for xtensa (ESP chips), with and without ESP-IDF.
• Reexport core::sync::atomic::* as-is for unknown targets, to avoid build failures if they don't have full atomic support.

• Add polyfill support for thumbv4t targets. (Nintendo Game Boy Advance)
• Added get_mut() to AtomicBool.
• Added into_inner() to all atomics
• Added fmt::Debug impl to AtomicBool, AtomicPtr.
• Added fmt::Pointer impl to AtomicPtr.
• Added From<*mut T> impl to AtomicPtr.
• Added RefUnwindSafe impl to all atomics.

• Updated critical-section to v0.2.5. Fixes std implementation to allow reentrant (nested) critical sections. This would previously deadlock.

• Added support for RISC-V.
• Added support for "full polyfill" level, where load/stores are polyfilled, not just CAS operations.
• Added support for AtomicU64, AtomicI64.

• Only import cortex-m when needed (#4)
• Fix panic on fetch_update due to incorrect ordering (#5)

• Added missing reexport of fence and compiler_fence in polyfilled mode.

• Added polyfills for AtomicU8, AtomicU16, AtomicUsize, AtomicI8, AtomicI16, AtomicI32, AtomicIsize

• First release