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;
}
}
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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();
}
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