1 | /* Shared Memory Lock Routines |
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2 | * |
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3 | * This shared memory locked queue support routine need to be |
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4 | * able to lock the specified locked queue. Interrupts are |
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5 | * disabled while the queue is locked to prevent preemption |
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6 | * and deadlock when two tasks poll for the same lock. |
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7 | * previous level. |
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8 | * |
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9 | * COPYRIGHT (c) 1989, 1990, 1991, 1992, 1993, 1994. |
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10 | * On-Line Applications Research Corporation (OAR). |
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11 | * All rights assigned to U.S. Government, 1994. |
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12 | * |
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13 | * This material may be reproduced by or for the U.S. Government pursuant |
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14 | * to the copyright license under the clause at DFARS 252.227-7013. This |
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15 | * notice must appear in all copies of this file and its derivatives. |
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16 | * |
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17 | * $Id$ |
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18 | */ |
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19 | |
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20 | #include <rtems.h> |
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21 | #include <bsp.h> |
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22 | #include <shm.h> |
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23 | |
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24 | #ifndef lint |
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25 | static char _sccsid[] = "@(#)lock.c 04/08/96 1.1\n"; |
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26 | #endif |
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27 | |
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28 | /* |
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29 | * Shm_Initialize_lock |
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30 | * |
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31 | * Initialize the lock for the specified locked queue. |
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32 | */ |
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33 | |
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34 | void Shm_Initialize_lock( |
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35 | Shm_Locked_queue_Control *lq_cb |
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36 | ) |
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37 | { |
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38 | lq_cb->lock = LQ_UNLOCKED; |
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39 | } |
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40 | |
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41 | /* void _Shm_Lock( &lq_cb ) |
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42 | * |
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43 | * This shared memory locked queue support routine locks the |
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44 | * specified locked queue. It disables interrupts to prevent |
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45 | * a deadlock condition. |
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46 | */ |
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47 | |
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48 | void Shm_Lock( |
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49 | Shm_Locked_queue_Control *lq_cb |
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50 | ) |
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51 | { |
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52 | rtems_unsigned32 isr_level; |
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53 | rtems_unsigned32 *lockptr = &lq_cb->lock; |
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54 | rtems_unsigned32 lock_value; |
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55 | |
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56 | lock_value = 0x80000000; |
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57 | rtems_interrupt_disable( isr_level ); |
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58 | |
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59 | Shm_isrstat = isr_level; |
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60 | while ( lock_value ) { |
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61 | asm volatile( "" |
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62 | : "=r" (lockptr), "=r" (lock_value) |
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63 | : "0" (lockptr), "1" (lock_value) |
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64 | ); |
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65 | /* |
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66 | * If not available, then may want to delay to reduce load on lock. |
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67 | */ |
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68 | |
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69 | if ( lock_value ) |
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70 | delay( 10 ); /* approximately 10 microseconds */ |
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71 | } |
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72 | } |
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73 | |
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74 | /* |
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75 | * Shm_Unlock |
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76 | * |
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77 | * Unlock the lock for the specified locked queue. |
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78 | */ |
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79 | |
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80 | void Shm_Unlock( |
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81 | Shm_Locked_queue_Control *lq_cb |
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82 | ) |
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83 | { |
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84 | rtems_unsigned32 isr_level; |
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85 | |
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86 | lq_cb->lock = SHM_UNLOCK_VALUE; |
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87 | isr_level = Shm_isrstat; |
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88 | rtems_interrupt_enable( isr_level ); |
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89 | } |
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90 | |
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