80 lines
1.9 KiB
C
80 lines
1.9 KiB
C
/*
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* This file is part of the libopencm3 project.
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*
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* Copyright (C) 2012 Fergus Noble <fergusnoble@gmail.com>
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*
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* This library is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Lesser General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public License
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* along with this library. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include <libopencm3/cm3/sync.h>
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/* DMB is supported on CM0 */
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void __dmb()
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{
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__asm__ volatile ("dmb");
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}
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/* Those are defined only on CM3 or CM4 */
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#if defined(__ARM_ARCH_7M__) || defined(__ARM_ARCH_7EM__)
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uint32_t __ldrex(volatile uint32_t *addr)
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{
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uint32_t res;
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__asm__ volatile ("ldrex %0, [%1]" : "=r" (res) : "r" (addr));
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return res;
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}
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uint32_t __strex(uint32_t val, volatile uint32_t *addr)
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{
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uint32_t res;
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__asm__ volatile ("strex %0, %2, [%1]"
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: "=&r" (res) : "r" (addr), "r" (val));
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return res;
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}
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void mutex_lock(mutex_t *m)
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{
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while (!mutex_trylock(m));
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}
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/* returns 1 if the lock was acquired */
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uint32_t mutex_trylock(mutex_t *m)
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{
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uint32_t status = 1;
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/* If the mutex is unlocked. */
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if (__ldrex(m) == MUTEX_UNLOCKED) {
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/* Try to lock it. */
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status = __strex(MUTEX_LOCKED, m);
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}
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/* Execute the mysterious Data Memory Barrier instruction! */
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__dmb();
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/* Did we get the lock? If not then try again
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* by calling this function once more. */
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return status == 0;
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}
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void mutex_unlock(mutex_t *m)
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{
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/* Ensure accesses to protected resource are finished */
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__dmb();
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/* Free the lock. */
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*m = MUTEX_UNLOCKED;
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}
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#endif
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