嵌入式操作系统内核原理和开发(实时系统中的定时器).doc

软件英才网 软件行业驰名招聘网站嵌入式操作系统内核原理和开发（实时系统中的定时器） 关于定时器的内容，其实我们之前也讨论过，也书写过相应的代码，但是表达得比较晦涩，效率也比较低。所以我们这里重新再讲一下定时器的相关代码，看看嵌入式系统中的定时器是怎么实现的。在我们之前讨论线程延时的时候就使用hash的方法，将不同的线程归类到不同的延时队列当中，并且按照时间长短先后排列，这样在最短的时间内就可以寻找到最合适的线程了。本质上，线程延时和定时器的基本原理是一样的。唯一的区别就是，线程延时响应的优先级要高一些，而定时器一般由独立线程完成，rawos也是这么做的。cpp view plaincopy1 void timer_task(void *pa) 2 3 RAW_U16 position; 4 LIST *timer_head_ptr; 5 LIST *iter; 6 LIST *iter_temp; 7 RAW_TIMER *timer_ptr; 8 9 timer_sem.count = 0; 10 11 while (1) 12 13 /*timer task will be blocked after call this function*/ 14 raw_semaphore_get(&timer_sem, RAW_WAIT_FOREVER); 15 16 /*Disable the system schedule we do not need disable interrupt since nothing to do with interrupt*/ 17 raw_disable_sche(); 18 19 /*calculate which timer_head*/ 20 raw_timer_count+; 21 position = (RAW_U16)(raw_timer_count & (TIMER_HEAD_NUMBERS - 1) ); 22 timer_head_ptr = &timer_headposition; 23 24 iter =timer_head_ptr-next; 25 26 while (RAW_TRUE) 27 /*if timer exits*/ 28 if (iter !=timer_head_ptr) 29 /*Must use iter_temp because iter may be remove later.*/ 30 iter_temp = iter-next; 31 timer_ptr = list_entry(iter, RAW_TIMER, timer_list); 32 33 /*if timeout*/ 34 if (raw_timer_count = timer_ptr-match) 35 36 /*remove form timer list*/ 37 timer_list_remove(timer_ptr); 38 /*if timer is reschedulable*/ 39 if (timer_ptr-reschedule_ticks) 40 /*Sort by remain time*/ 41 timer_ptr-remain = timer_ptr-reschedule_ticks; 42 43 timer_ptr-match = raw_timer_count + timer_ptr-remain; 44 position = (RAW_U16)(timer_ptr-match & (TIMER_HEAD_NUMBERS - 1); 45 timer_ptr-to_head = &timer_headposition; 46 timer_list_priority_insert(&timer_headposition, timer_ptr); 47 48 49 50 /*Any way both condition need to call registered timer function*/ 51 52 if (timer_ptr-raw_timeout_function) 53 timer_ptr-raw_timeout_function(timer_ptr-raw_timeout_param); 54 55 56 57 iter = iter_temp; 58 59 60 else 61 62 break; 63 64 65 66 67 /*exit because timer is not exit*/ 68 else 69 70 break; 71 72 73 74 75 raw_enable_sche(); 76 77 78 由于基本原理和之前的线程延时是一样的，所以这里就不重复了。定时器的基本操作其实也不多，主要包括定时器创建、启动定时器、修改定时器、关闭定时器、删除定时器共五个基本函数，大家可以和我一起慢慢看过来。cpp view plaincopy79 RAW_U16 raw_timer_create(RAW_TIMER *timer_ptr, RAW_U8 *name_ptr, 80 RAW_VOID (*expiration_function)(RAW_U32), RAW_U32 expiration_input, 81 RAW_U32 initial_ticks, RAW_U32 reschedule_ticks, RAW_U8 auto_activate) 82 83 84 85 #if (RAW_TIMER_FUNCTION_CHECK 0) 86 87 if (timer_ptr = 0) 88 return RAW_NULL_OBJECT; 89 90 91 if (expiration_function = 0) 92 return RAW_NULL_POINTER; 93 94 95 #endif 96 97 timer_ptr-name = name_ptr; 98 timer_ptr-raw_timeout_function = expiration_function; 99 timer_ptr-raw_timeout_param = expiration_input; 100 timer_ptr-init_count = initial_ticks; 101 timer_ptr-reschedule_ticks = reschedule_ticks; 102 timer_ptr-remain = 0; 103 timer_ptr-match = 0; 104 timer_ptr-timer_state = TIMER_DEACTIVE; 105 timer_ptr-to_head = 0; 106 107 list_init(&timer_ptr-timer_list); 108 109 if (auto_activate) 110 111 raw_timer_activate(timer_ptr); 112 113 114 return RAW_SUCCESS; 115 116 创建定时器的操作很简单，主要是把输入的参数存入到RAW_TIMER结构里面。相关的参数包括名称、函数指针、函数参数、初始tick、循环tick、标志参数。当然，由于定时器分为单次定时和循环定时两种，所以这里会有两个参数，如果不是循环定时器，循环tick参数可以不用配置。cpp view plaincopy117 RAW_U16 raw_timer_activate(RAW_TIMER *timer_ptr) 118 119 RAW_U16 position; 120 RAW_SR_ALLOC(); 121 122 #if (RAW_TIMER_FUNCTION_CHECK 0) 123 124 if (timer_ptr = 0) 125 return RAW_NULL_OBJECT; 126 127 128 #endif 129 130 /*Timer state TIMER_ACTIVE TIMER_DELETED is not allowed to delete*/ 131 if (timer_ptr-timer_state = TIMER_ACTIVE) 132 return RAW_TIMER_STATE_INVALID; 133 134 if (timer_ptr-timer_state = TIMER_DELETED) 135 return RAW_TIMER_STATE_INVALID; 136 137 RAW_CRITICAL_ENTER(); 138 timer_ptr-match = raw_timer_count + timer_ptr-init_count; 139 position = (RAW_U16)(timer_ptr-match & (TIMER_HEAD_NUMBERS - 1) ); 140 /*Sort by remain time*/ 141 timer_ptr-remain = timer_ptr-init_count; 142 /*Used by timer delete*/ 143 timer_ptr-to_head = &timer_headposition; 144 145 timer_list_priority_insert(&timer_headposition, timer_ptr); 146 timer_ptr-timer_state = TIMER_ACTIVE; 147 148 RAW_CRITICAL_EXIT(); 149 150 151 return RAW_SUCCESS; 152 153 启动定时器，就是把tick加入到定时器队列当中，看看timer_list_priority_insert这个函数你就明白了。因为整个函数的处理过程涉及到 全局变量timer_head，所以需要在前后面添加中断的处理动作。cpp view plaincopy154 RAW_U16 raw_timer_change(RAW_TIMER *timer_ptr, RAW_U32 initial_ticks, RAW_U32 reschedule_ticks) 155 156 RAW_SR_ALLOC(); 157 158 #if (RAW_TIMER_FUNCTION_CHECK 0) 159 160 if (timer_ptr = 0) 161 return RAW_NULL_OBJECT; 162 163 164 #endif 165 166 /*Only timer state TIMER_DEACTIVE is not allowed here*/ 167 if (timer_ptr-timer_state != TIMER_DEACTIVE) 168 return RAW_TIMER_STATE_INVALID; 169 170 171 if (timer_ptr-timer_state = TIMER_DELETED) 172 return RAW_TIMER_STATE_INVALID; 173 174 175 RAW_CRITICAL_ENTER(); 176 timer_ptr-init_count = initial_ticks; 177 timer_ptr-reschedule_ticks = reschedule_ticks; 178 RAW_CRITICAL_EXIT(); 179 return RAW_SUCCESS; 180 定时器修改函数就是把初始tick和循环tick修改一下，当然如果此时定时器还没有运行，初始tick还有用。但是一旦定时器起作用了，起作用的就只能是循环tick了，这一点大家要好好注意。cpp view plaincopy181 RAW_U16 raw_timer_deactivate(RAW_TIMER *timer_ptr) 182 183 RAW_SR_ALLOC(); 184 185 #if (RAW_TIMER_FUNCTION_CHECK 0) 186 187 if (timer_ptr = 0) 188 return RAW_NULL_OBJECT; 189 190 191 #endif 192 193 /*Timer state TIMER_DEACTIVE TIMER_DELETED is not allowed to delete*/ 194 if (timer_ptr-timer_state = TIMER_DEACTIVE) 195 return RAW_TIMER_STATE_INVALID; 196 197 198 if (timer_ptr-timer_state = TIMER_DELETED) 199 return RAW_TIMER_STATE_INVALID; 200 201 202 203 RAW_CRITICAL_ENTER(); 204 timer_list_remove(timer_ptr); 205 timer_ptr-timer_state = TIMER_DEACTIVE; 206 RAW_CRITICAL_EXIT(); 207 208 return RAW_SUCCESS; 209 210 211 停止定时器，顾名思义就是将定时器从队列中删除，同时设置状态为T