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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) 1989-1999.

 *  On-Line Applications Research Corporation (OAR).

 *

 *  The license and distribution terms for this file may be

 *  found in the file LICENSE in this distribution or at

 *  http://www.OARcorp.com/rtems/license.html.

 *

 *  $Id: lock.c,v 1.2 2001-09-27 11:59:40 chris Exp $

 */

#include <rtems.h>

#include <bsp.h>

#include <shm_driver.h>

#ifndef lint

static char _sccsid[] = "@(#)lock.c 04/08/96     1.1\n";

#endif

/*

 *  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;

  rtems_unsigned32 *lockptr = &lq_cb->lock;

  rtems_unsigned32 lock_value;

  lock_value = 0x80000000;

  rtems_interrupt_disable( isr_level );

    Shm_isrstat = isr_level;

    while ( lock_value ) {

      asm volatile( ""

                         : "=r" (lockptr), "=r" (lock_value)

                         : "0" (lockptr),  "1" (lock_value)

                  );

      /*

       *  If not available, then may want to delay to reduce load on lock.

       */

      if ( lock_value )

        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 );

}