延时操作是操作系统中经常遇到的一种情形。延时的原因很多,有的时候是为了等待外设芯片处理结束,有的时候是为了暂时释放cpu的使用权,有的就是为了希望在一段时间获取资源,如果没法在单位时间内获取,放弃等待。但是不管怎么说,延时都是操作系统必不可少的一个工作。下面我们就看看延时是怎么实现的,
static void tick_list_priority_insert(LIST *head, RAW_TASK_OBJ *task_ptr) { RAW_U32 val; LIST *q,*start, *end; RAW_TASK_OBJ *task_iter_temp; start = end = head; val = task_ptr->tick_remain; for (q = start->next; q != end; q = q->next) { task_iter_temp = list_entry(q, RAW_TASK_OBJ, tick_list); /*sorted by remain time*/ if ((task_iter_temp->tick_match - raw_tick_count) > val) { break; } } list_insert(q, &task_ptr->tick_list); } void tick_list_insert(RAW_TASK_OBJ *task_ptr, RAW_U32 time) { LIST *tick_head_ptr; RAW_U16 spoke; if (time) { task_ptr->tick_match = raw_tick_count + time; task_ptr->tick_remain = time; spoke = (RAW_U16)(task_ptr->tick_match & (TICK_HEAD_ARRAY - 1) ); tick_head_ptr = &tick_head[spoke]; tick_list_priority_insert(tick_head_ptr, task_ptr); task_ptr->tick_head = tick_head_ptr; } } |
延时的代码其实不是很多,所以我在这里把最重要的两个函数给粘贴到这里了。因为每个线程都有可能延时,那么怎么处理这些线程之间的关系就是我们需要做的事情了。我们看到了,我们直接用tick_match表示线程需要等待的那个时间点就可以了。当然,tick是不断增加的,我们可以把尾数相同的线程按照高低顺序排列在一起,这样在对应的tick到来的时候,就直接按照尾数查找就可以了,tick_list_priority_insert就是干了这么一件事情。
那么,tick什么时候到期呢?到期又该怎么处理呢,我们接着往下看,
void tick_list_update(void) { LIST *tick_head_ptr; RAW_TASK_OBJ *p_tcb; LIST *iter; LIST *iter_temp; RAW_U16 spoke; RAW_SR_ALLOC(); RAW_CRITICAL_ENTER(); raw_tick_count++; spoke = (RAW_U16)(raw_tick_count & (TICK_HEAD_ARRAY - 1) ); tick_head_ptr = &tick_head[spoke]; iter = tick_head_ptr->next; while (RAW_TRUE) { /*search all the time list if possible*/ if (iter != tick_head_ptr) { iter_temp = iter->next; p_tcb = list_entry(iter, RAW_TASK_OBJ, tick_list); /*Since time list is sorted by remain time, so just campare the absolute time*/ if (raw_tick_count == p_tcb->tick_match) { switch (p_tcb->task_state) { case RAW_DLY: p_tcb->block_status = RAW_B_OK; p_tcb->task_state = RAW_RDY; tick_list_remove(p_tcb); add_ready_list(&raw_ready_queue, p_tcb); break; case RAW_PEND_TIMEOUT: p_tcb->block_status = RAW_B_TIMEOUT; p_tcb->task_state = RAW_RDY; p_tcb->block_obj = 0; tick_list_remove(p_tcb); /*remove task on the block list because task is timeout*/ list_delete(&p_tcb->task_list); add_ready_list(&raw_ready_queue, p_tcb); break; case RAW_PEND_TIMEOUT_SUSPENDED: p_tcb->block_status = RAW_B_TIMEOUT; p_tcb->task_state = RAW_SUSPENDED; p_tcb->block_obj = 0; tick_list_remove(p_tcb); /*remove task on the block list because task is timeout*/ list_delete(&p_tcb->task_list); break; case RAW_DLY_SUSPENDED: p_tcb->task_state = RAW_SUSPENDED; p_tcb->block_status = RAW_B_OK; tick_list_remove(p_tcb); break; default: #if (CONFIG_RAW_ASSERT > 0) RAW_ASSERT(0); #endif break; } iter = iter_temp; } /*if current task time out absolute time is not equal current system time, just break because timer list is sorted*/ else { break; } } /*finish all the time list search */ else { break; } } RAW_CRITICAL_EXIT(); } |