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/************************************************************************/
/* */
/* File: sem.c */
/* Description: semaphore P and V operations. */
/* Version: 1.0 */
/* Author: Otto Mattik */
/* */
/* (C)Copyright Otto Mattik 2014-2021. */
/* */
/* This file is a part of 'armen' (a tiny operating system). */
/* 'armen' is distributed under the CeCILL-V2.1 licence. For more */
/* details about this licence, please visit the website cecill.info */
/* */
/************************************************************************/
#ifdef USE_SEM
#include "core.h"
/*
* initialize a semaphore
*
* input:
* sem address of semaphore
* value initial value for semaphore
* output:
*/
void sem_init( sem_t* sem, uint8_t value )
{
((_sem_t*)sem)->lock = 0;
((_sem_t*)sem)->value =
((_sem_t*)sem)->count = value;
}
/*
* P operation
*
* input:
* sem address of semaphore
* output:
* O if success, otherwise -1
*/
void sem_wait( sem_t* sem )
{
while( test_and_set( sem ) != 0 ) ;
if( ((_sem_t*)sem)->count == 0 )
{
((_sem_t*)sem)->lock = 0;
_threads[_cur_thread].sem = sem;
wait_event( EVENT_SEM );
}
else
{
--((_sem_t*)sem)->count;
((_sem_t*)sem)->lock = 0;
}
}
/*
* V operation
*
* input:
* sem address of semaphore
* output:
* O if success, otherwise -1
*/
void sem_post( sem_t* sem )
{
while( test_and_set( sem ) != 0 ) ;
if( ((_sem_t*)sem)->count != ((_sem_t*)sem)->value )
{
++((_sem_t*)sem)->count;
_wakeup( EVENT_SEM, sem );
}
((_sem_t*)sem)->lock = 0;
}
#endif
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