source: rtems/c/src/lib/libbsp/no_cpu/no_bsp/shmsupp/lock.c @ 7f6a24ab

4.104.114.84.95
Last change on this file since 7f6a24ab was ac7d5ef0, checked in by Joel Sherrill <joel.sherrill@…>, on May 11, 1995 at 5:39:37 PM

Initial revision

  • Property mode set to 100644
File size: 2.0 KB
Line 
1/*  Shared Memory Lock Routines
2 *
3 *  This shared memory locked queue support routine need to be
4 *  able to lock the specified locked queue.  Interrupts are
5 *  disabled while the queue is locked to prevent preemption
6 *  and deadlock when two tasks poll for the same lock.
7 *  previous level.
8 *
9 *  COPYRIGHT (c) 1989, 1990, 1991, 1992, 1993, 1994.
10 *  On-Line Applications Research Corporation (OAR).
11 *  All rights assigned to U.S. Government, 1994.
12 *
13 *  This material may be reproduced by or for the U.S. Government pursuant
14 *  to the copyright license under the clause at DFARS 252.227-7013.  This
15 *  notice must appear in all copies of this file and its derivatives.
16 *
17 *  $Id$
18 */
19
20#include <rtems.h>
21#include <bsp.h>
22#include <shm.h>
23
24/*
25 *  Shm_Initialize_lock
26 *
27 *  Initialize the lock for the specified locked queue.
28 */
29
30void Shm_Initialize_lock(
31  Shm_Locked_queue_Control *lq_cb
32)
33{
34  lq_cb->lock = LQ_UNLOCKED;
35}
36
37/*  void _Shm_Lock( &lq_cb )
38 *
39 *  This shared memory locked queue support routine locks the
40 *  specified locked queue.  It disables interrupts to prevent
41 *  a deadlock condition.
42 */
43
44void Shm_Lock(
45  Shm_Locked_queue_Control *lq_cb
46)
47{
48  rtems_unsigned32 isr_level;
49  rtems_unsigned32 *lockptr = &lq_cb->lock;
50  rtems_unsigned32 lock_value;
51
52  lock_value = 0x80000000;
53  rtems_interrupt_disable( isr_level );
54
55    Shm_isrstat = isr_level;
56    while ( lock_value ) {
57      asm volatile( ""
58                         : "=r" (lockptr), "=r" (lock_value)
59                         : "0" (lockptr),  "1" (lock_value)
60                  );
61      /*
62       *  If not available, then may want to delay to reduce load on lock.
63       */
64
65      if ( lock_value )
66        delay( 10 );   /* approximately 10 microseconds */
67   }
68}
69
70/*
71 *  Shm_Unlock
72 *
73 *  Unlock the lock for the specified locked queue.
74 */
75
76void Shm_Unlock(
77  Shm_Locked_queue_Control *lq_cb
78)
79{
80  rtems_unsigned32 isr_level;
81
82  lq_cb->lock = SHM_UNLOCK_VALUE;
83  isr_level = Shm_isrstat;
84  rtems_interrupt_enable( isr_level );
85}
86
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