openmv/src/omv/common/mutex.c
2021-05-12 23:19:10 +02:00

105 lines
2.5 KiB
C

/*
* This file is part of the OpenMV project.
*
* Copyright (c) 2013-2021 Ibrahim Abdelkader <iabdalkader@openmv.io>
* Copyright (c) 2013-2021 Kwabena W. Agyeman <kwagyeman@openmv.io>
*
* This work is licensed under the MIT license, see the file LICENSE for details.
*
* 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_gcc.h"
#include "py/mphal.h"
void mutex_init0(mutex_t *mutex)
{
__DMB();
mutex->tid = 0;
mutex->lock = 0;
mutex->last_tid = 0;
}
static void _mutex_lock(mutex_t *mutex, uint32_t tid, bool blocking)
{
#if (CPU==cortex-m0)
do {
__disable_irq();
if (mutex->lock == 0) {
mutex->lock = 1;
mutex->tid = tid;
}
__enable_irq();
__WFI();
} while (mutex->tid != tid && blocking);
#else
do {
// Attempt exclusive read
while (__LDREXW(&mutex->lock) != 0);
// Attempt to lock mutex
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 *mutex, uint32_t tid)
{
_mutex_lock(mutex, tid, true);
}
int mutex_try_lock(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);
}
return (mutex->tid == tid);
}
int mutex_try_lock_alternate(mutex_t *mutex, uint32_t tid)
{
if (mutex->last_tid != tid) {
if (mutex_try_lock(mutex, tid)) {
mutex->last_tid = tid;
return 1;
}
}
return 0;
}
int mutex_lock_timeout(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(mutex_t *mutex, uint32_t tid)
{
if (mutex->tid == tid) {
__DMB();
mutex->tid = 0;
mutex->lock = 0;
}
}