nordic mesh 任务调度实现
nordic mesh的任务调度室基于定时器实现的，有两个链表结构维护任务。
需要注意的是，任务调度的部分接口只能在“bearer event”的中段级别被调用，因此调用的形式是通过设置"bearer event"事件来实现的。
结构及接口 @timer_scheduler.h
任务调度的结构定义如下：
typedef enum
{
TIMER_EVENT_STATE_UNUSED, /**< Not present in the scheduler */
TIMER_EVENT_STATE_ADDED, /**< Added for processing */
TIMER_EVENT_STATE_QUEUED, /**< Queued for firing */
TIMER_EVENT_STATE_RESCHEDULED, /**< Rescheduled, but not resorted */
TIMER_EVENT_STATE_ABORTED, /**< Aborted, but still in the list */
TIMER_EVENT_STATE_IGNORED, /**< Aborted, but added for processing */
TIMER_EVENT_STATE_IN_CALLBACK /**< Currently being called */
} timer_event_state_t;
/**
* Timer event structure for schedulable timers.
*/
typedef struct timer_event
{
volatile timer_event_state_t state; /**< Timer event state. */
timestamp_t timestamp; /**< 定时器激发时间 */
timer_sch_callback_t cb; /**< 定时器激发时的回调函数 */
uint32_t interval; /**< 周期事件的时间间隔，0时表示单次事件 */
void * p_context; /**< 调用回调函数cb时传入的参数 */
struct timer_event* p_next; /**< 指向下一个事件结构的指针，构成链表 */
} timer_event_t;相关的几个接口如下：
/**
* Initializes the scheduler module.
* 在nrf_mesh_init()中被调用
*/
void timer_sch_init(void);
/**
* Schedules a timer event.
*
* @warning This function must be called from @ref BEARER_EVENT "bearer event" IRQ level or lower.
* 该函数必须在BEARER_EVENT的中断优先级上被调用
* @warning The structure parameters must not be changed after the structure has been added to the
* scheduler, as this may cause race conditions. If a change in timing is needed, please use the
* @ref timer_sch_reschedule() function. If any other changes are needed, abort the event, change the
* parameter, and schedule it again.
*
* @param[in] p_timer_evt A pointer to a statically allocated timer event, which will be used as
* context for the schedulable event.
*/
void timer_sch_schedule(timer_event_t* p_timer_evt);
/**
* Aborts a previously scheduled event.
*
* @warning This function must be called from @ref BEARER_EVENT "bearer event" IRQ level or lower.
* 该函数必须在BEARER_EVENT的中断优先级上被调用
* @param[in] p_timer_evt A pointer to a previously scheduled event.
*/
void timer_sch_abort(timer_event_t* p_timer_evt);
/**
* Reschedules a previously scheduled event.
*
* @warning This function must be called from @ref BEARER_EVENT "bearer event" IRQ level or lower.
* 该函数必须在BEARER_EVENT的中断优先级上被调用
* @param[in] p_timer_evt A pointer to a previously scheduled event.
* @param[in] new_timestamp When the event should time out, instead of the old time.
*/
void timer_sch_reschedule(timer_event_t* p_timer_evt, timestamp_t new_timestamp);任务调度实现 @timer_scheduler.c
调度器中维护两个任务链表p_head、p_add_head，当有新的任务加入调度时，首先会加到p_add_head链表中，此时新任务的状态会设置为"TIMER_EVENT_STATE_ADDED"；之后在process_add_list()函数遍历p_add_head链表，将其中状态为"TIMER_EVENT_STATE_ADDED"的任务加入到第一个链表p_head中。定时器激发时会遍历第一个链表，将其中满足运行时间的事件运行。
调度器结构的定义如下：
typedef struct
{
timer_event_t* p_head;
timer_event_t* p_add_head;
uint32_t dirty_events; /**< Events in the fire list that needs processing */
uint32_t event_count;
} scheduler_t;
/**
* Static globals
*/
static volatile scheduler_t m_scheduler; /**<调度器实体 */
static bearer_event_flag_t m_event_flag; /**<bearer event 事件 */需要注意的是，部分定时器接口是在”bearer event“的中断优先级的被调用的。因此，定义了m_event_flag的全局变量，以产生bearer-event事件调用。
timer_sch_init()
调度器初始化函数的实现代码如下，在其中首先将调度器实体全部归零，然后注册了一个bearer-event事件。
void timer_sch_init(void)
{
// 调度器结构置零
memset((scheduler_t*) &m_scheduler, 0, sizeof(m_scheduler));
// 注册一个bearer-event事件
// 当调用函数 bearer_event_flag_set(m_event_flag) 时
// 会产生bearer-event中断，来调用flag_event_cb()回调函数
m_event_flag = bearer_event_flag_add(flag_event_cb);
}bearer-event事件回调函数
static bool flag_event_cb(void)
{
/* 处理被污染的任务
* 被污染的任务要么直接移除
* 需要再次调度的，则加入到p_add_head链表中
*/
process_dirty_events();
/* add all the popped events back in, at their right places.
* 该函数遍历第二个链表，将其中的新加的任务添加到第一个链表中
* 第一个链表的任务是根据运行时间排序的，从头到尾运行时间越来越晚
* 即第一个链表的链表头是最先运行的节点
*/
process_add_list();
/* 激发定时器
* 遍历第一个链表，一次运行到达运行时间的任务
* p_head依次后移
*/
fire_timers(timer_now());
/*
* 设置定时器函数下次激发时间
*/
setup_timeout(timer_now());
return true;
}timer_sch_schedule()函数实现如下：
// 任务加入调度时，首先是加入第二个任务链表中
void timer_sch_schedule(timer_event_t* p_timer_evt)
{
NRF_MESH_ASSERT(p_timer_evt != NULL);
NRF_MESH_ASSERT(p_timer_evt->cb != NULL);
uint32_t was_masked;
_DISABLE_IRQS(was_masked);
p_timer_evt->p_next = NULL;
add_to_add_list(p_timer_evt);
_ENABLE_IRQS(was_masked);
bearer_event_flag_set(m_event_flag);
}timer_sch_abort()
终止某个任务
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void timer_sch_abort(timer_event_t* p_timer_evt)
{
NRF_MESH_ASSERT(p_timer_evt != NULL);
uint32_t was_masked;
_DISABLE_IRQS(was_masked);
if (p_timer_evt->state == TIMER_EVENT_STATE_IN_CALLBACK)
{
p_timer_evt->state = TIMER_EVENT_STATE_UNUSED;
}
else if (p_timer_evt->state == TIMER_EVENT_STATE_ADDED)
{
p_timer_evt->state = TIMER_EVENT_STATE_IGNORED;
}
else if (p_timer_evt->state != TIMER_EVENT_STATE_UNUSED)
{
if (!is_dirty_state(p_timer_evt->state))
{
m_scheduler.dirty_events++;
}
p_timer_evt->state = TIMER_EVENT_STATE_ABORTED;
bearer_event_flag_set(m_event_flag);
}
_ENABLE_IRQS(was_masked);
}timer_sch_reschedule()
再次调度
void timer_sch_reschedule(timer_event_t* p_timer_evt, timestamp_t new_timeout)
{
NRF_MESH_ASSERT(p_timer_evt != NULL);
uint32_t was_masked;
_DISABLE_IRQS(was_masked);
/* The events in the added queue will reinsert themselves in the processing. */
if (p_timer_evt->state == TIMER_EVENT_STATE_UNUSED ||
p_timer_evt->state == TIMER_EVENT_STATE_IN_CALLBACK)
{
add_to_add_list(p_timer_evt);
}
else if (p_timer_evt->state == TIMER_EVENT_STATE_ADDED ||
p_timer_evt->state == TIMER_EVENT_STATE_IGNORED)
{
p_timer_evt->state = TIMER_EVENT_STATE_ADDED;
}
else
{
/* Mark the rescheduled event as dirty, will be processed at the next opportunity. */
if (!is_dirty_state(p_timer_evt->state))
{
m_scheduler.dirty_events++;
}
p_timer_evt->state = TIMER_EVENT_STATE_RESCHEDULED;
}
p_timer_evt->timestamp = new_timeout;
bearer_event_flag_set(m_event_flag);
_ENABLE_IRQS(was_masked);
}