semaphore.c

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/*
 *  The contents of this file are subject to the Mozilla Public License
 *  Version 1.0 (the "License"); you may not use this file except in
 *  compliance with the License. You may obtain a copy of the License at
 *  http://www.mozilla.org/MPL/
 *
 *  Software distributed under the License is distributed on an "AS IS"
 *  basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See the
 *  License for the specific language governing rights and limitations
 *  under the License.
 *
 *  The Original Code is legOS code, released October 17, 1999.
 *
 *  The Initial Developer of the Original Code is Markus L. Noga.
 *  Portions created by Markus L. Noga are Copyright (C) 1999
 *  Markus L. Noga. All Rights Reserved.
 *
 *  Contributor(s): Markus L. Noga <markus@noga.de>
 */

#include <semaphore.h>

#ifdef CONF_SEMAPHORES

#include <unistd.h>

//
// Functions
//


wakeup_t sem_event_wait(wakeup_t data) {
        sem_t *sem=(sem_t*) ((unsigned)data);
        
        // we're called by the scheduler, therefore in an IRQ handler,
        // so no worrying about IRQs.
        //
        if(*sem) {
                (*sem)--;
                return 1;                       // sem!=0 -> wakeup
        }
        return 0;
}


int sem_wait(sem_t * sem) {
        // check if semaphore is available, if not, go to sleep
        
        if(sem_trywait(sem))
                if (wait_event(sem_event_wait,(unsigned long) ((unsigned)sem)) == 0)
                        return -1;
        
        return 0;
}

typedef struct {
        sem_t  *sem;
        time_t abs_timeout;
} timeout_sem_data_t;

static wakeup_t sem_event_timeout_wait(wakeup_t data) {
        timeout_sem_data_t *tsem = (timeout_sem_data_t*) ((unsigned)data);
        
        // we're called by the scheduler, therefore in an IRQ handler,
        // so no worrying about IRQs.
        //
        if (*tsem->sem) {
                (*tsem->sem)--;
                return 1;                       // sem!=0 -> wakeup
        }
        
        if (tsem->abs_timeout <= get_system_up_time()) {
                return 2;                       // timeout reached -> wakeup
        }

        return 0;
}

int sem_timedwait(sem_t *sem,
                  const time_t abs_timeout) {
        timeout_sem_data_t data;
        data.sem = sem;
        data.abs_timeout = abs_timeout;
        
        if (sem_trywait(sem)) {
                if (wait_event(sem_event_timeout_wait, 
                               (wakeup_t) ((unsigned) &data)) != 1) {
                        return -1; // timeout reached.
                }
        }
        return 0;
}


int sem_trywait(sem_t * sem);
#ifndef DOXYGEN_SHOULD_SKIP_THIS
__asm__("\n\
.text\n\
.align 1\n\
.globl _sem_trywait\n\
       _sem_trywait:\n\
        stc ccr,r1h                             ; save flags    \n\
        orc #0x80,ccr                           ; block all but NMI\n\
        mov.b @r0,r1l\n\
        beq sem_fail                            ; !=0 -> decrease, return 0\n\
        dec r1l\n\
        mov.b r1l,@r0\n\
        sub.w r0,r0                             ; return 0\n\
        bra sem_ok\n\
\n\
 sem_fail:\n\
        mov #0xffff,r0                          ; else return 0xffff\n\
\n\
 sem_ok:\n\
        ldc r1h,ccr                             ; restore flags\n\
        rts\n\
        ");
#endif // DOXYGEN_SHOULD_SKIP_THIS
        
#endif // CONF_SEMAPHORES

---