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/* Shared Memory Lock Routines
*
* This shared memory locked queue support routine need to be
* able to lock the specified locked queue. Interrupts are
* disabled while the queue is locked to prevent preemption
* and deadlock when two tasks poll for the same lock.
* previous level.
*
* COPYRIGHT (c) 1989, 1990, 1991, 1992, 1993, 1994.
* On-Line Applications Research Corporation (OAR).
* All rights assigned to U.S. Government, 1994.
*
* This material may be reproduced by or for the U.S. Government pursuant
* to the copyright license under the clause at DFARS 252.227-7013. This
* notice must appear in all copies of this file and its derivatives.
*
* $Id$
*/
#include <rtems.h>
#include <bsp.h>
#include <shm.h>
/*
* Shm_Initialize_lock
*
* Initialize the lock for the specified locked queue.
*/
void Shm_Initialize_lock(
Shm_Locked_queue_Control *lq_cb
)
{
lq_cb->lock = LQ_UNLOCKED;
}
/* void _Shm_Lock( &lq_cb )
*
* This shared memory locked queue support routine locks the
* specified locked queue. It disables interrupts to prevent
* a deadlock condition.
*/
void Shm_Lock(
Shm_Locked_queue_Control *lq_cb
)
{
rtems_unsigned32 isr_level;
volatile rtems_unsigned32 *lockptr = &lq_cb->lock;
rtems_unsigned32 lock_value;
lock_value = SHM_LOCK_VALUE;
rtems_interrupt_disable( isr_level );
Shm_isrstat = isr_level;
while ( 1 ) {
asm volatile( "lock ; xchg (%0),%1"
: "=r" (lockptr), "=r" (lock_value)
: "0" (lockptr), "1" (lock_value)
);
if ( lock_value == SHM_UNLOCK_VALUE )
break;
delay( 10 ); /* approximately 10 microseconds */
}
}
/*
* Shm_Unlock
*
* Unlock the lock for the specified locked queue.
*/
void Shm_Unlock(
Shm_Locked_queue_Control *lq_cb
)
{
rtems_unsigned32 isr_level;
lq_cb->lock = SHM_UNLOCK_VALUE;
isr_level = Shm_isrstat;
rtems_interrupt_enable( isr_level );
}
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