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NIIBE Yutaka
291
ChibiOS_2.0.2/os/kernel/src/chsem.c
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291
ChibiOS_2.0.2/os/kernel/src/chsem.c
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/*
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ChibiOS/RT - Copyright (C) 2006,2007,2008,2009,2010 Giovanni Di Sirio.
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This file is part of ChibiOS/RT.
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ChibiOS/RT is free software; you can redistribute it and/or modify
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it under the terms of the GNU 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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ChibiOS/RT 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 General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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---
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A special exception to the GPL can be applied should you wish to distribute
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a combined work that includes ChibiOS/RT, without being obliged to provide
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the source code for any proprietary components. See the file exception.txt
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for full details of how and when the exception can be applied.
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*/
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/**
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* @file chsem.c
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* @brief Semaphores code.
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*
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* @addtogroup semaphores
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* @details Semaphores related APIs and services.
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*
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* <h2>Operation mode</h2>
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* Semaphores are a flexible synchronization primitive, ChibiOS/RT
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* implements semaphores in their "counting semaphores" variant as
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* defined by Edsger Dijkstra plus several enhancements like:
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* - Wait operation with timeout.
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* - Reset operation.
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* - Atomic wait+signal operation.
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* - Return message from the wait operation (OK, RESET, TIMEOUT).
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* .
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* The binary semaphores variant can be easily implemented using
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* counting semaphores.<br>
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* Operations defined for semaphores:
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* - <b>Signal</b>: The semaphore counter is increased and if the
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* result is non-positive then a waiting thread is removed from
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* the semaphore queue and made ready for execution.
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* - <b>Wait</b>: The semaphore counter is decreased and if the result
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* becomes negative the thread is queued in the semaphore and
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* suspended.
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* - <b>Reset</b>: The semaphore counter is reset to a non-negative
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* value and all the threads in the queue are released.
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* .
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* Semaphores can be used as guards for mutual exclusion zones
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* (note that mutexes are recommended for this kind of use) but
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* also have other uses, queues guards and counters as example.<br>
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* Semaphores usually use a FIFO queuing strategy but it is possible
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* to make them order threads by priority by enabling
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* @p CH_USE_SEMAPHORES_PRIORITY in @p chconf.h.<br>
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* In order to use the Semaphores APIs the @p CH_USE_SEMAPHORES
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* option must be enabled in @p chconf.h.
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* @{
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*/
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#include "ch.h"
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#if CH_USE_SEMAPHORES
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#if CH_USE_SEMAPHORES_PRIORITY
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#define sem_insert(tp, qp) prio_insert(tp, qp)
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#else
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#define sem_insert(tp, qp) queue_insert(tp, qp)
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#endif
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/**
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* @brief Initializes a semaphore with the specified counter value.
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*
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* @param[out] sp pointer to a @p Semaphore structure
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* @param[in] n initial value of the semaphore counter. Must be
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* non-negative.
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*/
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void chSemInit(Semaphore *sp, cnt_t n) {
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chDbgCheck((sp != NULL) && (n >= 0), "chSemInit");
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queue_init(&sp->s_queue);
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sp->s_cnt = n;
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}
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/**
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* @brief Performs a reset operation on the semaphore.
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* @note The released threads can recognize they were waked up by a reset
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* rather than a signal because the @p chSemWait() will return
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* @p RDY_RESET instead of @p RDY_OK.
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*
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* @param[in] sp pointer to a @p Semaphore structure
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* @param[in] n the new value of the semaphore counter. The value must
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* be non-negative.
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*/
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void chSemReset(Semaphore *sp, cnt_t n) {
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chSysLock();
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chSemResetI(sp, n);
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chSchRescheduleS();
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chSysUnlock();
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}
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/**
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* @brief Performs a reset operation on the semaphore.
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* @note The released threads can recognize they were waked up by a reset
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* rather than a signal because the @p chSemWait() will return
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* @p RDY_RESET instead of @p RDY_OK.
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* @note This function does not reschedule.
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*
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* @param[in] sp pointer to a @p Semaphore structure
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* @param[in] n the new value of the semaphore counter. The value must
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* be non-negative.
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*/
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void chSemResetI(Semaphore *sp, cnt_t n) {
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cnt_t cnt;
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chDbgCheck((sp != NULL) && (n >= 0), "chSemResetI");
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cnt = sp->s_cnt;
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sp->s_cnt = n;
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while (++cnt <= 0)
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chSchReadyI(lifo_remove(&sp->s_queue))->p_u.rdymsg = RDY_RESET;
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}
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/**
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* @brief Performs a wait operation on a semaphore.
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*
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* @param[in] sp pointer to a @p Semaphore structure
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* @retval RDY_OK if the semaphore was signaled or not taken.
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* @retval RDY_RESET if the semaphore was reset using @p chSemReset().
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*/
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msg_t chSemWait(Semaphore *sp) {
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msg_t msg;
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chSysLock();
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msg = chSemWaitS(sp);
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chSysUnlock();
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return msg;
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}
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/**
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* @brief Performs a wait operation on a semaphore.
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*
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* @param[in] sp pointer to a @p Semaphore structure
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* @retval RDY_OK if the semaphore was signaled or not taken.
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* @retval RDY_RESET if the semaphore was reset using @p chSemReset().
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*/
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msg_t chSemWaitS(Semaphore *sp) {
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chDbgCheck(sp != NULL, "chSemWaitS");
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if (--sp->s_cnt < 0) {
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currp->p_u.wtobjp = sp;
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sem_insert(currp, &sp->s_queue);
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chSchGoSleepS(THD_STATE_WTSEM);
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return currp->p_u.rdymsg;
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}
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return RDY_OK;
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}
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/**
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* @brief Performs a wait operation on a semaphore with timeout specification.
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*
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* @param[in] sp pointer to a @p Semaphore structure
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* @param[in] time the number of ticks before the operation timeouts,
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* the following special values are allowed:
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* - @a TIME_IMMEDIATE immediate timeout.
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* - @a TIME_INFINITE no timeout.
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* .
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* @retval RDY_OK if the semaphore was signaled or not taken.
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* @retval RDY_RESET if the semaphore was reset using @p chSemReset().
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* @retval RDY_TIMEOUT if the semaphore was not signaled or reset within the
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* specified timeout.
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*/
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msg_t chSemWaitTimeout(Semaphore *sp, systime_t time) {
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msg_t msg;
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chSysLock();
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msg = chSemWaitTimeoutS(sp, time);
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chSysUnlock();
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return msg;
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}
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/**
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* @brief Performs a wait operation on a semaphore with timeout specification.
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*
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* @param[in] sp pointer to a @p Semaphore structure
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* @param[in] time the number of ticks before the operation timeouts,
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* the following special values are allowed:
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* - @a TIME_IMMEDIATE immediate timeout.
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* - @a TIME_INFINITE no timeout.
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* .
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* @retval RDY_OK if the semaphore was signaled or not taken.
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* @retval RDY_RESET if the semaphore was reset using @p chSemReset().
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* @retval RDY_TIMEOUT if the semaphore was not signaled or reset within the
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* specified timeout.
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*/
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msg_t chSemWaitTimeoutS(Semaphore *sp, systime_t time) {
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chDbgCheck(sp != NULL, "chSemWaitTimeoutS");
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if (--sp->s_cnt < 0) {
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if (TIME_IMMEDIATE == time) {
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sp->s_cnt++;
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return RDY_TIMEOUT;
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}
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currp->p_u.wtobjp = sp;
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sem_insert(currp, &sp->s_queue);
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return chSchGoSleepTimeoutS(THD_STATE_WTSEM, time);
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}
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return RDY_OK;
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}
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/**
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* @brief Performs a signal operation on a semaphore.
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*
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* @param[in] sp pointer to a @p Semaphore structure
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*/
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void chSemSignal(Semaphore *sp) {
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chDbgCheck(sp != NULL, "chSemSignal");
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chSysLock();
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if (++sp->s_cnt <= 0)
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chSchWakeupS(fifo_remove(&sp->s_queue), RDY_OK);
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chSysUnlock();
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}
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/**
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* @brief Performs a signal operation on a semaphore.
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* @note This function does not reschedule.
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*
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* @param[in] sp pointer to a @p Semaphore structure
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*/
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void chSemSignalI(Semaphore *sp) {
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chDbgCheck(sp != NULL, "chSemSignalI");
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if (++sp->s_cnt <= 0) {
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/* note, it is done this way in order to allow a tail call on
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chSchReadyI().*/
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Thread *tp = fifo_remove(&sp->s_queue);
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tp->p_u.rdymsg = RDY_OK;
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chSchReadyI(tp);
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}
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}
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#if CH_USE_SEMSW
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/**
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* @brief Performs atomic signal and wait operations on two semaphores.
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* @note The function is available only if the @p CH_USE_SEMSW
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* option is enabled in @p chconf.h.
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*
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* @param[in] sps pointer to a @p Semaphore structure to be signaled
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* @param[in] spw pointer to a @p Semaphore structure to be wait on
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* @retval RDY_OK if the semaphore was signaled or not taken.
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* @retval RDY_RESET if the semaphore was reset using @p chSemReset().
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*/
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msg_t chSemSignalWait(Semaphore *sps, Semaphore *spw) {
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msg_t msg;
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chDbgCheck((sps != NULL) && (spw != NULL), "chSemSignalWait");
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chSysLock();
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if (++sps->s_cnt <= 0)
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chSchReadyI(fifo_remove(&sps->s_queue))->p_u.rdymsg = RDY_OK;
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if (--spw->s_cnt < 0) {
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Thread *ctp = currp;
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sem_insert(ctp, &spw->s_queue);
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ctp->p_u.wtobjp = spw;
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chSchGoSleepS(THD_STATE_WTSEM);
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msg = ctp->p_u.rdymsg;
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}
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else {
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chSchRescheduleS();
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msg = RDY_OK;
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}
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chSysUnlock();
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return msg;
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}
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#endif /* CH_USE_SEMSW */
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#endif /* CH_USE_SEMAPHORES */
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/** @} */
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