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Fix asm::delay() variability due to alignment #587

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Merged
merged 1 commit into from
Apr 14, 2025
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Fix asm::delay() variability due to alignment #587

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4 changes: 4 additions & 0 deletions cortex-m/src/asm.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,10 @@ pub fn delay(cycles: u32) {
let real_cycles = 1 + cycles / 2;
unsafe {
asm!(
// The `bne` on some cores (eg Cortex-M4) will take a different number of instructions
// depending on the alignment of the branch target. Set the alignment of the top of the
// loop to prevent surprising timing changes when the alignment of the delay() changes.
".p2align 3",
// Use local labels to avoid R_ARM_THM_JUMP8 relocations which fail on thumbv6m.
"1:",
"subs {}, #1",
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