1 | /** |
---|
2 | * @file |
---|
3 | * |
---|
4 | * @ingroup ScoreWatchdog |
---|
5 | * @brief Watchdog Tickle |
---|
6 | */ |
---|
7 | |
---|
8 | /* |
---|
9 | * COPYRIGHT (c) 1989-1999. |
---|
10 | * On-Line Applications Research Corporation (OAR). |
---|
11 | * |
---|
12 | * The license and distribution terms for this file may be |
---|
13 | * found in the file LICENSE in this distribution or at |
---|
14 | * http://www.rtems.com/license/LICENSE. |
---|
15 | */ |
---|
16 | |
---|
17 | #if HAVE_CONFIG_H |
---|
18 | #include "config.h" |
---|
19 | #endif |
---|
20 | |
---|
21 | #include <rtems/system.h> |
---|
22 | #include <rtems/score/isr.h> |
---|
23 | #include <rtems/score/watchdog.h> |
---|
24 | |
---|
25 | void _Watchdog_Tickle( |
---|
26 | Chain_Control *header |
---|
27 | ) |
---|
28 | { |
---|
29 | ISR_Level level; |
---|
30 | Watchdog_Control *the_watchdog; |
---|
31 | Watchdog_States watchdog_state; |
---|
32 | |
---|
33 | /* |
---|
34 | * See the comment in watchdoginsert.c and watchdogadjust.c |
---|
35 | * about why it's safe not to declare header a pointer to |
---|
36 | * volatile data - till, 2003/7 |
---|
37 | */ |
---|
38 | |
---|
39 | _ISR_Disable( level ); |
---|
40 | |
---|
41 | if ( _Chain_Is_empty( header ) ) |
---|
42 | goto leave; |
---|
43 | |
---|
44 | the_watchdog = _Watchdog_First( header ); |
---|
45 | |
---|
46 | /* |
---|
47 | * For some reason, on rare occasions the_watchdog->delta_interval |
---|
48 | * of the head of the watchdog chain is 0. Before this test was |
---|
49 | * added, on these occasions an event (which usually was supposed |
---|
50 | * to have a timeout of 1 tick would have a delta_interval of 0, which |
---|
51 | * would be decremented to 0xFFFFFFFF by the unprotected |
---|
52 | * "the_watchdog->delta_interval--;" operation. |
---|
53 | * This would mean the event would not timeout, and also the chain would |
---|
54 | * be blocked, because a timeout with a very high number would be at the |
---|
55 | * head, rather than at the end. |
---|
56 | * The test "if (the_watchdog->delta_interval != 0)" |
---|
57 | * here prevents this from occuring. |
---|
58 | * |
---|
59 | * We were not able to categorically identify the situation that causes |
---|
60 | * this, but proved it to be true empirically. So this check causes |
---|
61 | * correct behaviour in this circumstance. |
---|
62 | * |
---|
63 | * The belief is that a race condition exists whereby an event at the head |
---|
64 | * of the chain is removed (by a pending ISR or higher priority task) |
---|
65 | * during the _ISR_Flash( level ); in _Watchdog_Insert, but the watchdog |
---|
66 | * to be inserted has already had its delta_interval adjusted to 0, and |
---|
67 | * so is added to the head of the chain with a delta_interval of 0. |
---|
68 | * |
---|
69 | * Steven Johnson - 12/2005 (gcc-3.2.3 -O3 on powerpc) |
---|
70 | */ |
---|
71 | if (the_watchdog->delta_interval != 0) { |
---|
72 | the_watchdog->delta_interval--; |
---|
73 | if ( the_watchdog->delta_interval != 0 ) |
---|
74 | goto leave; |
---|
75 | } |
---|
76 | |
---|
77 | do { |
---|
78 | watchdog_state = _Watchdog_Remove( the_watchdog ); |
---|
79 | |
---|
80 | _ISR_Enable( level ); |
---|
81 | |
---|
82 | switch( watchdog_state ) { |
---|
83 | case WATCHDOG_ACTIVE: |
---|
84 | (*the_watchdog->routine)( |
---|
85 | the_watchdog->id, |
---|
86 | the_watchdog->user_data |
---|
87 | ); |
---|
88 | break; |
---|
89 | |
---|
90 | case WATCHDOG_INACTIVE: |
---|
91 | /* |
---|
92 | * This state indicates that the watchdog is not on any chain. |
---|
93 | * Thus, it is NOT on a chain being tickled. This case should |
---|
94 | * never occur. |
---|
95 | */ |
---|
96 | break; |
---|
97 | |
---|
98 | case WATCHDOG_BEING_INSERTED: |
---|
99 | /* |
---|
100 | * This state indicates that the watchdog is in the process of |
---|
101 | * BEING inserted on the chain. Thus, it can NOT be on a chain |
---|
102 | * being tickled. This case should never occur. |
---|
103 | */ |
---|
104 | break; |
---|
105 | |
---|
106 | case WATCHDOG_REMOVE_IT: |
---|
107 | break; |
---|
108 | } |
---|
109 | |
---|
110 | _ISR_Disable( level ); |
---|
111 | |
---|
112 | the_watchdog = _Watchdog_First( header ); |
---|
113 | } while ( !_Chain_Is_empty( header ) && |
---|
114 | (the_watchdog->delta_interval == 0) ); |
---|
115 | |
---|
116 | leave: |
---|
117 | _ISR_Enable(level); |
---|
118 | } |
---|