source: rtems/c/src/lib/libbsp/a29k/portsw/shmsupp/lock.c @ 0836603

4.104.114.84.95
Last change on this file since 0836603 was 0836603, checked in by Joel Sherrill <joel.sherrill@…>, on Sep 18, 1996 at 9:13:10 PM

new files submitted by Craig Lebakken (lebakken@…) and Derrick Ostertag
(ostertag@…)

  • Property mode set to 100644
File size: 2.1 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#ifndef lint
25static char _sccsid[] = "@(#)lock.c 04/08/96     1.1\n";
26#endif
27
28/*
29 *  Shm_Initialize_lock
30 *
31 *  Initialize the lock for the specified locked queue.
32 */
33
34void Shm_Initialize_lock(
35  Shm_Locked_queue_Control *lq_cb
36)
37{
38  lq_cb->lock = LQ_UNLOCKED;
39}
40
41/*  void _Shm_Lock( &lq_cb )
42 *
43 *  This shared memory locked queue support routine locks the
44 *  specified locked queue.  It disables interrupts to prevent
45 *  a deadlock condition.
46 */
47
48void Shm_Lock(
49  Shm_Locked_queue_Control *lq_cb
50)
51{
52  rtems_unsigned32 isr_level;
53  rtems_unsigned32 *lockptr = &lq_cb->lock;
54  rtems_unsigned32 lock_value;
55
56  lock_value = 0x80000000;
57  rtems_interrupt_disable( isr_level );
58
59    Shm_isrstat = isr_level;
60    while ( lock_value ) {
61      asm volatile( ""
62                         : "=r" (lockptr), "=r" (lock_value)
63                         : "0" (lockptr),  "1" (lock_value)
64                  );
65      /*
66       *  If not available, then may want to delay to reduce load on lock.
67       */
68
69      if ( lock_value )
70        delay( 10 );   /* approximately 10 microseconds */
71   }
72}
73
74/*
75 *  Shm_Unlock
76 *
77 *  Unlock the lock for the specified locked queue.
78 */
79
80void Shm_Unlock(
81  Shm_Locked_queue_Control *lq_cb
82)
83{
84  rtems_unsigned32 isr_level;
85
86  lq_cb->lock = SHM_UNLOCK_VALUE;
87  isr_level = Shm_isrstat;
88  rtems_interrupt_enable( isr_level );
89}
90
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