Initial vendor packages

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

vendor/portable-atomic/src/imp/interrupt/msp430.rs

@@ -0,0 +1,64 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+// Adapted from https://github.com/rust-embedded/msp430.
+//
+// See also src/imp/msp430.rs.
+//
+// Refs: https://www.ti.com/lit/ug/slau208q/slau208q.pdf
+
+#[cfg(not(portable_atomic_no_asm))]
+use core::arch::asm;
+
+pub(super) use super::super::msp430 as atomic;
+
+pub(super) type State = u16;
+
+/// Disables interrupts and returns the previous interrupt state.
+#[inline]
+pub(super) fn disable() -> State {
+    let r: State;
+    // SAFETY: reading the status 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.
+        // Do not use `preserves_flags` because DINT modifies the GIE (global interrupt enable) bit of the status register.
+        #[cfg(not(portable_atomic_no_asm))]
+        asm!(
+            "mov R2, {0}",
+            "dint {{ nop",
+            out(reg) r,
+            options(nostack),
+        );
+        #[cfg(portable_atomic_no_asm)]
+        {
+            llvm_asm!("mov R2, $0" : "=r"(r) ::: "volatile");
+            llvm_asm!("dint { nop" ::: "memory" : "volatile");
+        }
+    }
+    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) {
+    // SAFETY: the caller must guarantee that the state was retrieved by the previous `disable`,
+    unsafe {
+        // This clobbers the entire status register, but we never explicitly modify
+        // flags within a critical session, and the only flags that may be changed
+        // within a critical session are the arithmetic flags that are changed as
+        // a side effect of arithmetic operations, etc., which LLVM recognizes,
+        // so it is safe to clobber them here.
+        // See also the discussion at https://github.com/taiki-e/portable-atomic/pull/40.
+        //
+        // Do not use `nomem` and `readonly` because prevent preceding memory accesses from being reordered after interrupts are enabled.
+        // Do not use `preserves_flags` because MOV modifies the status register.
+        #[cfg(not(portable_atomic_no_asm))]
+        asm!("nop {{ mov {0}, R2 {{ nop", in(reg) r, options(nostack));
+        #[cfg(portable_atomic_no_asm)]
+        llvm_asm!("nop { mov $0, R2 { nop" :: "r"(r) : "memory" : "volatile");
+    }
+}