Document embedded-hal-bus features in README.md and Cargo.toml

Author: 9names

embedded-hal-bus/Cargo.toml

@@ -15,11 +15,24 @@ repository = "https://github.com/rust-embedded/embedded-hal"
 version = "0.2.0"
 
 [features]
+# Enable shared bus implementations using `std::sync::Mutex`, and implement `std::error::Error` for `DeviceError`
 std = []
+# Enable shared bus implementations that require Atomic CAS operations
 atomic-device = []
+# Enable `embedded-hal-async` support.
 async = ["dep:embedded-hal-async"]
+# Derive `defmt::Format` from `defmt` 0.3 for enums and structs. See https://github.com/knurling-rs/defmt for more info
 defmt-03 = ["dep:defmt-03", "embedded-hal/defmt-03", "embedded-hal-async?/defmt-03"]
+# Enable critical-section feature in portable-atomic.
+#
+# `portable-atomic` emulates atomic CAS functionality, allowing `embedded-hal-bus` to use `atomic-device` on hardware that does not natively support atomic CAS.
+# This feature requires a critical-section implementation, which is most often provided by your arch crate (cortex-m / riscv / msp430 / avr-device / etc) when the `critical-section-single-core` feature is enabled.
+# A list of critical-section impls is available [in the critical section docs](https://github.com/rust-embedded/critical-section?tab=readme-ov-file#usage-in-no-std-binaries)
 portable-atomic-critical-section = ["atomic-device", "portable-atomic/critical-section"]
+# Enable unsafe-assume-single-core feature of portable-atomic.
+# 
+# `portable-atomic` emulates atomic CAS functionality, allowing `embedded-hal-bus` to use `atomic-device` on hardware that does not natively support atomic CAS.
+#  This feature is only safe on single core systems
 portable-atomic-unsafe-assume-single-core = ["atomic-device", "portable-atomic/unsafe-assume-single-core"]
 
 [dependencies]

embedded-hal-bus/README.md

@@ -30,10 +30,20 @@ provides mechanisms to obtain multiple `I2c` instances out of a single `I2c` ins
 
 ## Optional Cargo features
 
-- **`std`**: enable shared bus implementations using `std::sync::Mutex`, and implement
-  `std::error::Error` for `DeviceError`.
 - **`async`**: enable `embedded-hal-async` support.
+- **`atomic-device`**: enable shared bus implementations that require Atomic CAS operations.
 - **`defmt-03`**: Derive `defmt::Format` from `defmt` 0.3 for enums and structs.
+- **`portable-atomic-critical-section`**: Enable critical-section feature in portable-atomic.
+
+  `portable-atomic` emulates atomic CAS functionality, allowing `embedded-hal-bus` to use `atomic-device` on hardware that does not natively support atomic CAS.
+  This feature requires a critical-section implementation, which is most often provided by your arch crate (cortex-m / riscv / msp430 / avr-device / etc) when the `critical-section-single-core` feature is enabled.
+  A list of critical-section impls is available [in the critical section docs](https://github.com/rust-embedded/critical-section?tab=readme-ov-file#usage-in-no-std-binaries)
+- **`portable-atomic-unsafe-assume-single-core`**: Enable unsafe-assume-single-core feature of portable-atomic.
+
+  `portable-atomic` emulates atomic CAS functionality, allowing `embedded-hal-bus` to use `atomic-device` on hardware that does not natively support atomic CAS.
+  This feature is only safe on single core systems
+- **`std`**: enable shared bus implementations using `std::sync::Mutex`, and implement
+  `std::error::Error` for `DeviceError`.
 
 ## Minimum Supported Rust Version (MSRV)