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