Initial vendor packages

Signed-off-by: Valentin Popov <valentin@popov.link>

vendor/portable-atomic/src/imp/interrupt/armv6m.rs

@@ -0,0 +1,48 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+// Adapted from https://github.com/rust-embedded/cortex-m.
+//
+// Generated asm:
+// - armv6-m https://godbolt.org/z/YxME38xcM
+
+#[cfg(not(portable_atomic_no_asm))]
+use core::arch::asm;
+
+pub(super) use core::sync::atomic;
+
+pub(super) type State = u32;
+
+/// Disables interrupts and returns the previous interrupt state.
+#[inline]
+pub(super) fn disable() -> State {
+    let r: State;
+    // SAFETY: reading the priority mask register and disabling interrupts are safe.
+    // (see module-level comments of interrupt/mod.rs on the safety of using privileged instructions)
+    unsafe {
+        // Do not use `nomem` and `readonly` because prevent subsequent memory accesses from being reordered before interrupts are disabled.
+        asm!(
+            "mrs {0}, PRIMASK",
+            "cpsid i",
+            out(reg) r,
+            options(nostack, preserves_flags),
+        );
+    }
+    r
+}
+
+/// Restores the previous interrupt state.
+///
+/// # Safety
+///
+/// The state must be the one retrieved by the previous `disable`.
+#[inline]
+pub(super) unsafe fn restore(r: State) {
+    if r & 0x1 == 0 {
+        // SAFETY: the caller must guarantee that the state was retrieved by the previous `disable`,
+        // and we've checked that interrupts were enabled before disabling interrupts.
+        unsafe {
+            // Do not use `nomem` and `readonly` because prevent preceding memory accesses from being reordered after interrupts are enabled.
+            asm!("cpsie i", options(nostack, preserves_flags));
+        }
+    }
+}