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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>
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/*
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* SPDX-License-Identifier: MIT
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*
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* Copyright (C) 2013-2024 OpenMV, LLC.
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* Copyright (C) 2013-2025 OpenMV, LLC.
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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@ -22,89 +22,39 @@
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* THE SOFTWARE.
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*
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* Mutex implementation.
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* This is a standard implementation of mutexs on ARM processors following the ARM guide.
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* http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dai0321a/BIHEJCHB.html
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*
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* Note: The Cortex-M0/M0+ does Not have the Load/Store exclusive instructions, on these
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* CPUs the locking function is implemented with atomic access using disable/enable IRQs.
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*/
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#include "mutex.h"
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#include "cmsis_compiler.h"
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#include "py/mphal.h"
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#include "common/mutex.h"
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void mutex_init0(omv_mutex_t *mutex) {
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__DMB();
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mutex->tid = 0;
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mutex->lock = 0;
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mutex->last_tid = 0;
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void mutex_init0(mutex_t *m) {
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atomic_store_explicit(&m->tid, 0, memory_order_relaxed);
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atomic_flag_clear_explicit(&m->lock, memory_order_relaxed);
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}
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static void _mutex_lock(omv_mutex_t *mutex, uint32_t tid, bool blocking) {
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#if (__ARM_ARCH < 7)
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do {
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__disable_irq();
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if (mutex->lock == 0) {
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mutex->lock = 1;
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mutex->tid = tid;
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}
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__enable_irq();
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} while (mutex->tid != tid && blocking);
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#else
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do {
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// Attempt to lock the mutex
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if (__LDREXW(&mutex->lock) == 0) {
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if (__STREXW(1, &mutex->lock) == 0) {
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// Set TID if mutex is locked
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mutex->tid = tid;
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}
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}
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} while (mutex->tid != tid && blocking);
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#endif
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__DMB();
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void mutex_lock(mutex_t *m, size_t tid) {
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while (atomic_flag_test_and_set_explicit(&m->lock, memory_order_acquire));
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atomic_store_explicit(&m->tid, tid, memory_order_release);
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}
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void mutex_lock(omv_mutex_t *mutex, uint32_t tid) {
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_mutex_lock(mutex, tid, true);
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}
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int mutex_try_lock(omv_mutex_t *mutex, uint32_t tid) {
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// If the mutex is already locked by the current thread then
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// release it and return without locking, otherwise try to lock it.
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if (mutex->tid == tid) {
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mutex_unlock(mutex, tid);
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} else {
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_mutex_lock(mutex, tid, false);
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bool mutex_try_lock(mutex_t *m, size_t tid) {
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if (!atomic_flag_test_and_set_explicit(&m->lock, memory_order_acquire)) {
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atomic_store_explicit(&m->tid, tid, memory_order_release);
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return true;
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}
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return (mutex->tid == tid);
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return false;
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}
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int mutex_try_lock_alternate(omv_mutex_t *mutex, uint32_t tid) {
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if (mutex->last_tid != tid) {
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if (mutex_try_lock(mutex, tid)) {
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mutex->last_tid = tid;
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return 1;
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bool mutex_try_lock_fair(mutex_t *m, size_t tid) {
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if (atomic_load_explicit(&m->tid, memory_order_acquire) != tid) {
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if (!atomic_flag_test_and_set_explicit(&m->lock, memory_order_acquire)) {
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atomic_store_explicit(&m->tid, tid, memory_order_release);
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return true;
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}
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}
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return 0;
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return false;
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}
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int mutex_lock_timeout(omv_mutex_t *mutex, uint32_t tid, uint32_t timeout) {
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mp_uint_t tick_start = mp_hal_ticks_ms();
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while ((mp_hal_ticks_ms() - tick_start) >= timeout) {
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if (mutex_try_lock(mutex, tid)) {
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return 1;
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}
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__WFI();
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}
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return 0;
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}
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void mutex_unlock(omv_mutex_t *mutex, uint32_t tid) {
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if (mutex->tid == tid) {
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__DMB();
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mutex->tid = 0;
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mutex->lock = 0;
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void mutex_unlock(mutex_t *m, size_t tid) {
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if (atomic_load_explicit(&m->tid, memory_order_acquire) == tid) {
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atomic_flag_clear_explicit(&m->lock, memory_order_release);
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}
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}
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@ -1,7 +1,7 @@
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/*
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* SPDX-License-Identifier: MIT
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*
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* Copyright (C) 2013-2024 OpenMV, LLC.
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* Copyright (C) 2013-2025 OpenMV, LLC.
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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@ -26,19 +26,27 @@
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#ifndef __MUTEX_H__
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#define __MUTEX_H__
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#include <stdint.h>
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#define MUTEX_TID_IDE (1 << 0)
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#define MUTEX_TID_OMV (1 << 1)
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#include <stdbool.h>
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#include <stddef.h>
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#include <stdatomic.h>
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// Conflicts with picosdk
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#define mutex_t omv_mutex_t
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typedef enum {
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MUTEX_TID_IDE = 1,
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MUTEX_TID_OMV = 2
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} mutex_tid_t;
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typedef volatile struct {
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uint32_t tid;
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uint32_t lock;
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uint32_t last_tid;
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} omv_mutex_t;
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atomic_size_t tid;
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atomic_flag lock;
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} mutex_t;
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void mutex_init0(omv_mutex_t *mutex);
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void mutex_lock(omv_mutex_t *mutex, uint32_t tid);
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int mutex_try_lock(omv_mutex_t *mutex, uint32_t tid);
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int mutex_try_lock_alternate(omv_mutex_t *mutex, uint32_t tid);
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int mutex_lock_timeout(omv_mutex_t *mutex, uint32_t tid, uint32_t timeout);
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void mutex_unlock(omv_mutex_t *mutex, uint32_t tid);
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#endif /* __MUTEX_H__ */
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void mutex_init0(mutex_t *mutex);
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void mutex_lock(mutex_t *mutex, size_t tid);
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bool mutex_try_lock(mutex_t *mutex, size_t tid);
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// Prevents a thread from locking twice in a row.
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bool mutex_try_lock_fair(mutex_t *mutex, size_t tid);
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void mutex_unlock(mutex_t *mutex, size_t tid);
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#endif // __MUTEX_H__
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