Add implementation for critical-section 1.0, for cortex-m v0.7.x

.github/workflows/ci.yml

@@ -13,13 +13,19 @@ jobs:
       matrix:
         # All generated code should be running on stable now
         rust: [stable]
+        features: ["", "critical-section-single-core"]
 
         include:
           # Test MSRV
           - rust: 1.38.0
+            features: ""
 
           # Test nightly but don't fail
           - rust: nightly
+            features: ""
+            experimental: true
+          - rust: nightly
+            features: "critical-section-single-core"
             experimental: true
     steps:
       - uses: actions/checkout@v2
@@ -29,6 +35,6 @@ jobs:
           toolchain: ${{ matrix.rust }}
           override: true
       - name: Run tests
-        run: cargo test --all
+        run: cargo test --all --features "${{ matrix.features }}"
 
 # FIXME: test on macOS and Windows

.github/workflows/clippy.yml

@@ -23,3 +23,4 @@ jobs:
       - uses: actions-rs/clippy-check@v1
         with:
           token: ${{ secrets.GITHUB_TOKEN }}
+          args: --features critical-section-single-core

CHANGELOG.md

@@ -7,6 +7,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ## [Unreleased]
 
+- Added `critical-section-single-core` feature which provides an implementation for the `critical_section` crate for single-core systems, based on disabling all interrupts. (#448)
+
 ## [v0.7.5] - 2022-05-15
 
 ### Deprecated

Cargo.toml

@@ -17,6 +17,7 @@ links = "cortex-m"  # prevent multiple versions of this crate to be linked toget
 
 [dependencies]
 bare-metal = { version = "0.2.4", features = ["const-fn"] }
+critical-section = { version = "1.0.0", optional = true }
 volatile-register = "0.2.0"
 bitfield = "0.13.2"
 embedded-hal = "0.2.4"
@@ -32,6 +33,7 @@ cm7-r0p1 = ["cm7"]
 inline-asm = []
 linker-plugin-lto = []
 std = []
+critical-section-single-core = ["critical-section/restore-state-bool"]
 
 [workspace]
 members = ["xtask", "cortex-m-semihosting", "panic-semihosting", "panic-itm"]

src/critical_section.rs

@@ -0,0 +1,25 @@
+#[cfg(all(cortex_m, feature = "critical-section-single-core"))]
+mod single_core_critical_section {
+    use critical_section::{set_impl, Impl, RawRestoreState};
+
+    use crate::interrupt;
+    use crate::register::primask;
+
+    struct SingleCoreCriticalSection;
+    set_impl!(SingleCoreCriticalSection);
+
+    unsafe impl Impl for SingleCoreCriticalSection {
+        unsafe fn acquire() -> RawRestoreState {
+            let was_active = primask::read().is_active();
+            interrupt::disable();
+            was_active
+        }
+
+        unsafe fn release(was_active: RawRestoreState) {
+            // Only re-enable interrupts if they were enabled before the critical section.
+            if was_active {
+                interrupt::enable()
+            }
+        }
+    }
+}

src/lib.rs

@@ -90,6 +90,7 @@ mod macros;
 pub mod asm;
 #[cfg(armv8m)]
 pub mod cmse;
+mod critical_section;
 pub mod delay;
 pub mod interrupt;
 #[cfg(all(not(armv6m), not(armv8m_base)))]

xtask/tests/ci.rs

@@ -44,20 +44,22 @@ fn build(package: &str, target: &str, features: &[&str]) {
 
 #[rustfmt::skip]
 static PACKAGE_FEATURES: &[(&str, &[&str], &[&str])] = &[
-    ("cortex-m", ALL_TARGETS, &["inline-asm", "cm7-r0p1"]), // no `linker-plugin-lto` since it's experimental
+    ("cortex-m", ALL_TARGETS, &["inline-asm", "cm7-r0p1", "critical-section-single-core"]), // no `linker-plugin-lto` since it's experimental
     ("cortex-m-semihosting", ALL_TARGETS, &["inline-asm", "no-semihosting", "jlink-quirks"]),
     ("panic-semihosting", ALL_TARGETS, &["inline-asm", "exit", "jlink-quirks"]),
     ("panic-itm", NON_BASE_TARGETS, &[]),
 ];
 
-fn check_crates_build(is_nightly: bool) {
+fn check_crates_build(is_nightly: bool, is_msrv: bool) {
     // Build all crates for each supported target.
     for (package, targets, all_features) in PACKAGE_FEATURES {
         for target in *targets {
             // Filters crate features, keeping only those that are supported.
             // Relies on all crates in this repo to use the same convention.
             let should_use_feature = |feat: &str| {
                 match feat {
+                    // critical-section doesn't build in 1.38 due to using `#[doc(include_str!(..))]`
+                    "critical-section-single-core" => !is_msrv,
                     // This is nightly-only, so don't use it on stable.
                     "inline-asm" => is_nightly,
                     // This only affects thumbv7em targets.
@@ -103,8 +105,9 @@ fn main() {
 
     let output = Command::new("rustc").arg("-V").output().unwrap();
     let is_nightly = str::from_utf8(&output.stdout).unwrap().contains("nightly");
+    let is_msrv = str::from_utf8(&output.stdout).unwrap().contains("1.38");
 
-    check_crates_build(is_nightly);
+    check_crates_build(is_nightly, is_msrv);
 
     // Check host-side applications of the crate.
     check_host_side();