common/mutex: Use C11 atomic operations.

Use C11 atomic operations to implement the mutex instead
of hard-coded intrinsics. This generates more efficient
assembly on newer ARM architectures by taking advantage
of the new LDA/STL instructions (and their exclusive variants),
which avoid full memory barriers while still providing
memory ordering guarantees.

Signed-off-by: iabdalkader <i.abdalkader@gmail.com>
This commit is contained in:
iabdalkader 2025-07-25 12:13:04 +02:00
parent a88d5e5b0c
commit 2c4b318ff9
2 changed files with 44 additions and 86 deletions

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@ -1,7 +1,7 @@
/*
* SPDX-License-Identifier: MIT
*
* Copyright (C) 2013-2024 OpenMV, LLC.
* Copyright (C) 2013-2025 OpenMV, LLC.
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
@ -22,89 +22,39 @@
* THE SOFTWARE.
*
* Mutex implementation.
* This is a standard implementation of mutexs on ARM processors following the ARM guide.
* http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dai0321a/BIHEJCHB.html
*
* Note: The Cortex-M0/M0+ does Not have the Load/Store exclusive instructions, on these
* CPUs the locking function is implemented with atomic access using disable/enable IRQs.
*/
#include "mutex.h"
#include "cmsis_compiler.h"
#include "py/mphal.h"
#include "common/mutex.h"
void mutex_init0(omv_mutex_t *mutex) {
__DMB();
mutex->tid = 0;
mutex->lock = 0;
mutex->last_tid = 0;
void mutex_init0(mutex_t *m) {
atomic_store_explicit(&m->tid, 0, memory_order_relaxed);
atomic_flag_clear_explicit(&m->lock, memory_order_relaxed);
}
static void _mutex_lock(omv_mutex_t *mutex, uint32_t tid, bool blocking) {
#if (__ARM_ARCH < 7)
do {
__disable_irq();
if (mutex->lock == 0) {
mutex->lock = 1;
mutex->tid = tid;
}
__enable_irq();
} while (mutex->tid != tid && blocking);
#else
do {
// Attempt to lock the mutex
if (__LDREXW(&mutex->lock) == 0) {
if (__STREXW(1, &mutex->lock) == 0) {
// Set TID if mutex is locked
mutex->tid = tid;
}
}
} while (mutex->tid != tid && blocking);
#endif
__DMB();
void mutex_lock(mutex_t *m, size_t tid) {
while (atomic_flag_test_and_set_explicit(&m->lock, memory_order_acquire));
atomic_store_explicit(&m->tid, tid, memory_order_release);
}
void mutex_lock(omv_mutex_t *mutex, uint32_t tid) {
_mutex_lock(mutex, tid, true);
}
int mutex_try_lock(omv_mutex_t *mutex, uint32_t tid) {
// If the mutex is already locked by the current thread then
// release it and return without locking, otherwise try to lock it.
if (mutex->tid == tid) {
mutex_unlock(mutex, tid);
} else {
_mutex_lock(mutex, tid, false);
bool mutex_try_lock(mutex_t *m, size_t tid) {
if (!atomic_flag_test_and_set_explicit(&m->lock, memory_order_acquire)) {
atomic_store_explicit(&m->tid, tid, memory_order_release);
return true;
}
return (mutex->tid == tid);
return false;
}
int mutex_try_lock_alternate(omv_mutex_t *mutex, uint32_t tid) {
if (mutex->last_tid != tid) {
if (mutex_try_lock(mutex, tid)) {
mutex->last_tid = tid;
return 1;
bool mutex_try_lock_fair(mutex_t *m, size_t tid) {
if (atomic_load_explicit(&m->tid, memory_order_acquire) != tid) {
if (!atomic_flag_test_and_set_explicit(&m->lock, memory_order_acquire)) {
atomic_store_explicit(&m->tid, tid, memory_order_release);
return true;
}
}
return 0;
return false;
}
int mutex_lock_timeout(omv_mutex_t *mutex, uint32_t tid, uint32_t timeout) {
mp_uint_t tick_start = mp_hal_ticks_ms();
while ((mp_hal_ticks_ms() - tick_start) >= timeout) {
if (mutex_try_lock(mutex, tid)) {
return 1;
}
__WFI();
}
return 0;
}
void mutex_unlock(omv_mutex_t *mutex, uint32_t tid) {
if (mutex->tid == tid) {
__DMB();
mutex->tid = 0;
mutex->lock = 0;
void mutex_unlock(mutex_t *m, size_t tid) {
if (atomic_load_explicit(&m->tid, memory_order_acquire) == tid) {
atomic_flag_clear_explicit(&m->lock, memory_order_release);
}
}

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@ -1,7 +1,7 @@
/*
* SPDX-License-Identifier: MIT
*
* Copyright (C) 2013-2024 OpenMV, LLC.
* Copyright (C) 2013-2025 OpenMV, LLC.
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
@ -26,19 +26,27 @@
#ifndef __MUTEX_H__
#define __MUTEX_H__
#include <stdint.h>
#define MUTEX_TID_IDE (1 << 0)
#define MUTEX_TID_OMV (1 << 1)
#include <stdbool.h>
#include <stddef.h>
#include <stdatomic.h>
// Conflicts with picosdk
#define mutex_t omv_mutex_t
typedef enum {
MUTEX_TID_IDE = 1,
MUTEX_TID_OMV = 2
} mutex_tid_t;
typedef volatile struct {
uint32_t tid;
uint32_t lock;
uint32_t last_tid;
} omv_mutex_t;
atomic_size_t tid;
atomic_flag lock;
} mutex_t;
void mutex_init0(omv_mutex_t *mutex);
void mutex_lock(omv_mutex_t *mutex, uint32_t tid);
int mutex_try_lock(omv_mutex_t *mutex, uint32_t tid);
int mutex_try_lock_alternate(omv_mutex_t *mutex, uint32_t tid);
int mutex_lock_timeout(omv_mutex_t *mutex, uint32_t tid, uint32_t timeout);
void mutex_unlock(omv_mutex_t *mutex, uint32_t tid);
#endif /* __MUTEX_H__ */
void mutex_init0(mutex_t *mutex);
void mutex_lock(mutex_t *mutex, size_t tid);
bool mutex_try_lock(mutex_t *mutex, size_t tid);
// Prevents a thread from locking twice in a row.
bool mutex_try_lock_fair(mutex_t *mutex, size_t tid);
void mutex_unlock(mutex_t *mutex, size_t tid);
#endif // __MUTEX_H__