1 // SPDX-License-Identifier: Apache-2.0 OR MIT
2
3 /*
4 Adapted from https://github.com/rust-embedded/msp430.
5
6 See also src/imp/msp430.rs.
7
8 Refs: https://www.ti.com/lit/ug/slau208q/slau208q.pdf
9 */
10
11 #[cfg(not(portable_atomic_no_asm))]
12 use core::arch::asm;
13
14 pub(super) use super::super::msp430 as atomic;
15
16 pub(super) type State = u16;
17
18 /// Disables interrupts and returns the previous interrupt state.
19 #[inline(always)]
disable() -> State20 pub(super) fn disable() -> State {
21 let r: State;
22 // SAFETY: reading the status register and disabling interrupts are safe.
23 // (see module-level comments of interrupt/mod.rs on the safety of using privileged instructions)
24 unsafe {
25 // Do not use `nomem` and `readonly` because prevent subsequent memory accesses from being reordered before interrupts are disabled.
26 // Do not use `preserves_flags` because DINT modifies the GIE (global interrupt enable) bit of the status register.
27 #[cfg(not(portable_atomic_no_asm))]
28 asm!(
29 "mov R2, {0}",
30 "dint {{ nop",
31 out(reg) r,
32 options(nostack),
33 );
34 #[cfg(portable_atomic_no_asm)]
35 {
36 llvm_asm!("mov R2, $0" : "=r"(r) ::: "volatile");
37 llvm_asm!("dint { nop" ::: "memory" : "volatile");
38 }
39 }
40 r
41 }
42
43 /// Restores the previous interrupt state.
44 ///
45 /// # Safety
46 ///
47 /// The state must be the one retrieved by the previous `disable`.
48 #[inline(always)]
restore(r: State)49 pub(super) unsafe fn restore(r: State) {
50 // SAFETY: the caller must guarantee that the state was retrieved by the previous `disable`,
51 unsafe {
52 // This clobbers the entire status register, but we never explicitly modify
53 // flags within a critical session, and the only flags that may be changed
54 // within a critical session are the arithmetic flags that are changed as
55 // a side effect of arithmetic operations, etc., which LLVM recognizes,
56 // so it is safe to clobber them here.
57 // See also the discussion at https://github.com/taiki-e/portable-atomic/pull/40.
58 //
59 // Do not use `nomem` and `readonly` because prevent preceding memory accesses from being reordered after interrupts are enabled.
60 // Do not use `preserves_flags` because MOV modifies the status register.
61 #[cfg(not(portable_atomic_no_asm))]
62 asm!("nop {{ mov {0}, R2 {{ nop", in(reg) r, options(nostack));
63 #[cfg(portable_atomic_no_asm)]
64 llvm_asm!("nop { mov $0, R2 { nop" :: "r"(r) : "memory" : "volatile");
65 }
66 }
67