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// 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");
}
}
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