首先是wd_start函數，調用該函數是爲了設置一個watchdog定時器。
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: wd_start
*
* Description:
* This function adds a watchdog timer to the active timer queue. The
* specified watchdog function at 'wdentry' will be called from the
* interrupt level after the specified number of ticks has elapsed.
* Watchdog timers may be started from the interrupt level.
*
* Watchdog timers execute in the address environment that was in effect
* when wd_start() is called.
*
* Watchdog timers execute only once.
*
* To replace either the timeout delay or the function to be executed,
* call wd_start again with the same wdog; only the most recent wdStart()
* on a given watchdog ID has any effect.
*
* Input Parameters:
* wdog - watchdog ID
* delay - Delay count in clock ticks
* wdentry - function to call on timeout
* parm1..4 - parameters to pass to wdentry
*
* Returned Value:
* Zero (OK) is returned on success; a negated errno value is return to
* indicate the nature of any failure.
*
* Assumptions:
* The watchdog routine runs in the context of the timer interrupt handler
* and is subject to all ISR restrictions.
*
****************************************************************************/
int wd_start(WDOG_ID wdog, int32_t delay, wdentry_t wdentry, int argc, ...)
{
va_list ap;
FAR struct wdog_s *curr;
FAR struct wdog_s *prev;
FAR struct wdog_s *next;
int32_t now;
irqstate_t flags;
int i;
/* Verify the wdog and setup parameters */
if (wdog == NULL || argc > CONFIG_MAX_WDOGPARMS || delay < 0)
{
return -EINVAL;
}
/* Check if the watchdog has been started. If so, stop it.
* NOTE: There is a race condition here... the caller may receive
* the watchdog between the time that wd_start is called and
* the critical section is established.
*/
flags = enter_critical_section();
if (WDOG_ISACTIVE(wdog))
{
wd_cancel(wdog);
}
/* Save the data in the watchdog structure */
wdog->func = wdentry; /* Function to execute when delay expires */
up_getpicbase(&wdog->picbase);
wdog->argc = argc;
va_start(ap, argc);
for (i = 0; i < argc; i++)
{
wdog->parm[i] = va_arg(ap, wdparm_t);
}
#ifdef CONFIG_DEBUG_FEATURES
for (; i < CONFIG_MAX_WDOGPARMS; i++)
{
wdog->parm[i] = 0;
}
#endif
va_end(ap);
/* Calculate delay+1, forcing the delay into a range that we can handle */
if (delay <= 0)
{
delay = 1;
}
else if (++delay <= 0)
{
delay--;
}
#ifdef CONFIG_SCHED_TICKLESS
/* Cancel the interval timer that drives the timing events. This will cause
* wd_timer to be called which update the delay value for the first time
* at the head of the timer list (there is a possibility that it could even
* remove it).
*/
***(void)sched_timer_cancel();***
#endif
/* Do the easy case first -- when the watchdog timer queue is empty. */
if (g_wdactivelist.head == NULL)
{
#ifdef CONFIG_SCHED_TICKLESS
/* Update clock tickbase */
g_wdtickbase = clock_systimer();
#endif
/* Add the watchdog to the head == tail of the queue. */
sq_addlast((FAR sq_entry_t *)wdog, &g_wdactivelist);
}
/* There are other active watchdogs in the timer queue */
else
{
now = 0;
prev = curr = (FAR struct wdog_s *)g_wdactivelist.head;
/* Advance to positive time */
while ((now += curr->lag) < 0 && curr->next)
{
prev = curr;
curr = curr->next;
}
/* Advance past shorter delays */
while (now <= delay && curr->next)
{
prev = curr;
curr = curr->next;
now += curr->lag;
}
/* Check if the new wdog must be inserted before the curr. */
if (delay < now)
{
/* The relative delay time is smaller or equal to the current delay
* time, so decrement the current delay time by the new relative
* delay time.
*/
delay -= (now - curr->lag);
curr->lag -= delay;
/* Insert the new watchdog in the list */
if (curr == (FAR struct wdog_s *)g_wdactivelist.head)
{
/* Insert the watchdog at the head of the list */
sq_addfirst((FAR sq_entry_t *)wdog, &g_wdactivelist);
}
else
{
/* Insert the watchdog in mid- or end-of-queue */
sq_addafter((FAR sq_entry_t *)prev, (FAR sq_entry_t *)wdog,
&g_wdactivelist);
}
}
/* The new watchdog delay time is greater than the curr delay time,
* so the new wdog must be inserted after the curr. This only occurs
* if the wdog is to be added to the end of the list.
*/
else
{
delay -= now;
if (!curr->next)
{
sq_addlast((FAR sq_entry_t *)wdog, &g_wdactivelist);
}
else
{
next = curr->next;
next->lag -= delay;
sq_addafter((FAR sq_entry_t *)curr, (FAR sq_entry_t *)wdog,
&g_wdactivelist);
}
}
}
/* Put the lag into the watchdog structure and mark it as active. */
wdog->lag = delay;
WDOG_SETACTIVE(wdog);
#ifdef CONFIG_SCHED_TICKLESS
/* Resume the interval timer that will generate the next interval event.
* If the timer at the head of the list changed, then this will pick that
* new delay.
*/
***sched_timer_resume();***
#endif
leave_critical_section(flags);
return OK;
}
int wd_start(WDOG_ID wdog, int32_t delay, wdentry_t wdentry, int argc, ...)第一個參
數WDOG_ID wdog是watchdog ID, 第二個參數 int32_t delay是延時的時間，第三個
參數wdentry_t wdentry是watchdod的entry函數， int argc, …是指傳遞給
wdentry的參數列表。
/* Advance to positive time */
while ((now += curr->lag) < 0 && curr->next)
{
prev = curr;
curr = curr->next;
}
這部分代碼是在g_wdactivelist不爲空的情況下去找延時delay的存放節點，要找到
介於當前要設置的watchdog的間隔時間的節點。
#ifdef CONFIG_SCHED_TICKLESS
/* Cancel the interval timer that drives the timing events. This will cause
* wd_timer to be called which update the delay value for the first time
* at the head of the timer list (there is a possibility that it could even
* remove it).
*/
(void)sched_timer_cancel();
#endif
#ifdef CONFIG_SCHED_TICKLESS
/* Cancel the interval timer that drives the timing events. This will cause
* wd_timer to be called which update the delay value for the first time
* at the head of the timer list (there is a possibility that it could even
* remove it).
*/
(void)sched_timer_cancel();
#endif
#ifdef CONFIG_SCHED_TICKLESS
/* Resume the interval timer that will generate the next interval event.
* If the timer at the head of the list changed, then this will pick that
* new delay.
*/
sched_timer_resume();
#endif
sched_timer_cancel()函數和sched_timer_resume()是成對
的，sched_timer_cancel是暫停當前的計時活動。而sched_timer_resume則是重新評估下一個截止日期並重新啓動間隔計時器。
對於sched_timer_cancel()函數來說，其實現如下圖所示：
/****************************************************************************
* Name: sched_timer_cancel
*
* Description:
* Stop the current timing activity. This is currently called just before
* a new entry is inserted at the head of a timer list and also as part
* of the processing of sched_timer_reassess().
*
* This function(1) cancels the current timer, (2) determines how much of
* the interval has elapsed, (3) completes any partially timed events
* (including updating the delay of the timer at the head of the timer
* list), and (2) returns the number of ticks that would be needed to
* resume timing and complete this delay.
*
* Input Parameters:
* None
*
* Returned Value:
* Number of timer ticks that would be needed to complete the delay (zero
* if the timer was not active).
*
****************************************************************************/
#ifdef CONFIG_SCHED_TICKLESS_ALARM
unsigned int sched_timer_cancel(void)
{
struct timespec ts;
unsigned int elapsed;
/* Cancel the alarm and and get the time that the alarm was cancelled.
* If the alarm was not enabled (or, perhaps, just expired since
* interrupts were disabled), up_timer_cancel() will return the
* current time.
*/
ts.tv_sec = g_stop_time.tv_sec;
ts.tv_nsec = g_stop_time.tv_nsec;
(void)up_alarm_cancel(&g_stop_time);
#ifdef CONFIG_SCHED_SPORADIC
/* Save the last time that the scheduler ran */
g_sched_time.tv_sec = g_stop_time.tv_sec;
g_sched_time.tv_nsec = g_stop_time.tv_nsec;
#endif
/* Convert this to the elapsed time */
clock_timespec_subtract(&g_stop_time, &ts, &ts);
/* Convert to ticks */
#ifdef CONFIG_HAVE_LONG_LONG
elapsed = SEC2TICK((uint64_t)ts.tv_sec);
#else
elapsed = SEC2TICK(ts.tv_sec);
#endif
elapsed += ts.tv_nsec / NSEC_PER_TICK;
/* Correct g_stop_time cause of the elapsed have remainder */
g_stop_time.tv_nsec -= ts.tv_nsec % NSEC_PER_TICK;
if (g_stop_time.tv_nsec < 0)
{
g_stop_time.tv_nsec += NSEC_PER_SEC;
g_stop_time.tv_sec--;
}
/* Process the timer ticks and return the next interval */
return nxsched_timer_process(elapsed, true);
}
#else
unsigned int sched_timer_cancel(void)
{
struct timespec ts;
unsigned int ticks;
unsigned int elapsed;
/* Get the time remaining on the interval timer and cancel the timer. */
(void)up_timer_cancel(&ts);
#ifdef CONFIG_SCHED_SPORADIC
/* Save the last time that the scheduler ran */
g_sched_time.tv_sec = ts.tv_sec;
g_sched_time.tv_nsec = ts.tv_nsec;
#endif
/* Convert to ticks */
#ifdef CONFIG_HAVE_LONG_LONG
ticks = SEC2TICK((uint64_t)ts.tv_sec);
#else
ticks = SEC2TICK(ts.tv_sec);
#endif
ticks += NSEC2TICK(ts.tv_nsec);
DEBUGASSERT(ticks <= g_timer_interval);
/* Handle the partial timer. This will reassess all timer conditions and
* re-start the interval timer with the correct delay. Context switches
* are not permitted in this case because we are not certain of the
* calling conditions.
*/
elapsed = g_timer_interval - ticks;
g_timer_interval = 0;
/* Process the timer ticks and return the next interval */
return nxsched_timer_process(elapsed, true);
}
#endif
sched_timer_resume()作用是重新評估下一個截止日期並重新啓動間隔計時器，其
實先函數如下所示：
/****************************************************************************
* Name: sched_timer_resume
*
* Description:
* Re-assess the next deadline and restart the interval timer. This is
* called from wd_start() after it has inserted a new delay into the
* timer list.
*
* Input Parameters:
* None
*
* Returned Value:
* None.
*
* Assumptions:
* This function is called right after sched_timer_cancel(). If
* CONFIG_SCHED_TICKLESS_ALARM=y, then g_stop_time must be the value time
* when the timer was cancelled.
*
****************************************************************************/
void sched_timer_resume(void)
{
unsigned int nexttime;
#ifdef CONFIG_SCHED_SPORADIC
/* Save the last time that the scheduler ran */
(void)up_timer_gettime(&g_sched_time);
#endif
/* Reassess the next deadline (by simply processing a zero ticks expired)
* and set up the next interval (or not).
*/
//nxsched_timer_process返回下一次watchdog timer要delay的時
間，nxsched_timer_start是要啓動下一次的watchdog timer.
nexttime = nxsched_timer_process(0, true);
nxsched_timer_start(nexttime);
}
nxsched_timer_process()函數的實現如下所示，其功能是找出下一個節點的watchdog的有效delay時間，給nxsched_timer_start()用於啓動下一次的timer。
/****************************************************************************
* Name: nxsched_timer_process
*
* Description:
* Process events on timer expiration.
*
* Input Parameters:
* ticks - The number of ticks that have elapsed on the interval timer.
* noswitches - True: Can't do context switches now.
*
* Returned Value:
* The number of ticks to use when setting up the next timer. Zero if
* there is no interesting event to be timed.
*
****************************************************************************/
static unsigned int nxsched_timer_process(unsigned int ticks,
bool noswitches)
{
unsigned int cmptime = UINT_MAX;
unsigned int rettime = 0;
unsigned int tmp;
#ifdef CONFIG_CLOCK_TIMEKEEPING
/* Process wall time */
clock_update_wall_time();
#endif
/* Process watchdogs */
tmp = wd_timer(ticks);
if (tmp > 0)
{
cmptime = tmp;
rettime = tmp;
}
/* Check for operations specific to scheduling policy of the currently
* active task.
*/
tmp = nxsched_process_scheduler(ticks, noswitches);
if (tmp > 0 && tmp < cmptime)
{
rettime = tmp;
}
return rettime;
}
wd_timer函數是用於找到下一個timer的時間，其實先如下：
/****************************************************************************
* Name: wd_timer
*
* Description:
* This function is called from the timer interrupt handler to determine
* if it is time to execute a watchdog function. If so, the watchdog
* function will be executed in the context of the timer interrupt
* handler.
*
* Input Parameters:
* ticks - If CONFIG_SCHED_TICKLESS is defined then the number of ticks
* in the interval that just expired is provided. Otherwise,
* this function is called on each timer interrupt and a value of one
* is implicit.
*
* Returned Value:
* If CONFIG_SCHED_TICKLESS is defined then the number of ticks for the
* next delay is provided (zero if no delay). Otherwise, this function
* has no returned value.
*
* Assumptions:
* Called from interrupt handler logic with interrupts disabled.
*
****************************************************************************/
#ifdef CONFIG_SCHED_TICKLESS
unsigned int wd_timer(int ticks)
{
FAR struct wdog_s *wdog;
#ifdef CONFIG_SMP
irqstate_t flags;
#endif
unsigned int ret;
int decr;
#ifdef CONFIG_SMP
/* We are in an interrupt handler as, as a consequence, interrupts are
* disabled. But in the SMP case, interrupts MAY be disabled only on
* the local CPU since most architectures do not permit disabling
* interrupts on other CPUS.
*
* Hence, we must follow rules for critical sections even here in the
* SMP case.
*/
flags = enter_critical_section();
#endif
/* Check if there are any active watchdogs to process */
while (g_wdactivelist.head != NULL && ticks > 0)
{
/* Get the watchdog at the head of the list */
wdog = (FAR struct wdog_s *)g_wdactivelist.head;
#ifndef CONFIG_SCHED_TICKLESS_ALARM
/* There is logic to handle the case where ticks is greater than
* the watchdog lag, but if the scheduling is working properly
* that should never happen.
*/
DEBUGASSERT(ticks <= wdog->lag);
#endif
/* Decrement the lag for this watchdog. */
decr = MIN(wdog->lag, ticks);
/* There are. Decrement the lag counter */
wdog->lag -= decr;
ticks -= decr;
g_wdtickbase += decr;
/* Check if the watchdog at the head of the list is ready to run */
wd_expiration();
}
/* Update clock tickbase */
g_wdtickbase += ticks;
/* Return the delay for the next watchdog to expire */
ret = g_wdactivelist.head ?
((FAR struct wdog_s *)g_wdactivelist.head)->lag : 0;
#ifdef CONFIG_SMP
leave_critical_section(flags);
#endif
/* Return the delay for the next watchdog to expire */
return ret;
}
#else
void wd_timer(void)
{
#ifdef CONFIG_SMP
irqstate_t flags;
/* We are in an interrupt handler as, as a consequence, interrupts are
* disabled. But in the SMP case, interrupts MAY be disabled only on
* the local CPU since most architectures do not permit disabling
* interrupts on other CPUS.
*
* Hence, we must follow rules for critical sections even here in the
* SMP case.
*/
flags = enter_critical_section();
#endif
/* Check if there are any active watchdogs to process */
if (g_wdactivelist.head)
{
/* There are. Decrement the lag counter */
--(((FAR struct wdog_s *)g_wdactivelist.head)->lag);
/* Check if the watchdog at the head of the list is ready to run */
wd_expiration();
}
#ifdef CONFIG_SMP
leave_critical_section(flags);
#endif
}
#endif /* CONFIG_SCHED_TICKLESS */
wd_expiration()函數用於檢查watchdog list head節點的是否準備好去運行了，其實先如下所示：
/****************************************************************************
* Name: wd_expiration
*
* Description:
* Check if the timer for the watchdog at the head of list is ready to
* run. If so, remove the watchdog from the list and execute it.
*
* Input Parameters:
* None
*
* Returned Value:
* None
*
****************************************************************************/
static inline void wd_expiration(void)
{
FAR struct wdog_s *wdog;
/* Check if the watchdog at the head of the list is ready to run */
if (((FAR struct wdog_s *)g_wdactivelist.head)->lag <= 0)
{
/* Process the watchdog at the head of the list as well as any
* other watchdogs that became ready to run at this time
*/
while (g_wdactivelist.head &&
((FAR struct wdog_s *)g_wdactivelist.head)->lag <= 0)
{
/* Remove the watchdog from the head of the list */
wdog = (FAR struct wdog_s *)sq_remfirst(&g_wdactivelist);
/* If there is another watchdog behind this one, update its
* its lag (this shouldn't be necessary).
*/
if (g_wdactivelist.head)
{
((FAR struct wdog_s *)g_wdactivelist.head)->lag += wdog->lag;
}
/* Indicate that the watchdog is no longer active. */
WDOG_CLRACTIVE(wdog);
/* Execute the watchdog function */
up_setpicbase(wdog->picbase);
#if CONFIG_MAX_WDOGPARMS == 0
wdog->func(0);
#elif CONFIG_MAX_WDOGPARMS == 1
wdog->func((int)wdog->argc,
wdog->parm[0]);
#elif CONFIG_MAX_WDOGPARMS == 2
wdog->func((int)wdog->argc,
wdog->parm[0], wdog->parm[1]);
#elif CONFIG_MAX_WDOGPARMS == 3
wdog->func((int)wdog->argc,
wdog->parm[0], wdog->parm[1], wdog->parm[2]);
#elif CONFIG_MAX_WDOGPARMS == 4
wdog->func((int)wdog->argc,
wdog->parm[0], wdog->parm[1], wdog->parm[2],
wdog->parm[3]);
#else
# error Missing support
#endif
}
}
}
nxsched_process_scheduler函數的功能是如果系統支持RR和sporadic調度，則算出這兩種調度所允許的調度時間去和
wd_timer函數返回的下一個watchdog list節點的delay時間做
比較，然後的出最小的時間去啓動下一次的timer. 如果系統支持的是FIFO調度，則該函數返回的是0。
/****************************************************************************
* Name: nxsched_process_scheduler
*
* Description:
* Check for operations specific to scheduling policy of the currently
* active task on a single CPU.
*
* Input Parameters:
* ticks - The number of ticks that have elapsed on the interval timer.
* noswitches - True: Can't do context switches now.
*
* Returned Value:
* The number if ticks remaining until the next time slice expires.
* Zero is returned if there is no time slicing (i.e., the task at the
* head of the ready-to-run list does not support round robin
* scheduling).
*
* The value one may returned under certain circumstances that probably
* can't happen. The value one is the minimal timer setup and it means
* that a context switch is needed now, but cannot be performed because
* noswitches == true.
*
****************************************************************************/
#if CONFIG_RR_INTERVAL > 0 || defined(CONFIG_SCHED_SPORADIC)
static uint32_t nxsched_process_scheduler(uint32_t ticks, bool noswitches)
{
#ifdef CONFIG_SMP
uint32_t minslice = UINT32_MAX;
uint32_t timeslice;
irqstate_t flags;
int i;
/* If we are running on a single CPU architecture, then we know interrupts
* a disabled an there is no need to explicitly call
* enter_critical_section(). However, in the SMP case,
* enter_critical_section() does much more than just disable interrupts on
* the local CPU; it also manages spinlocks to assure the stability of the
* TCB that we are manipulating.
*/
flags = enter_critical_section();
/* Perform scheduler operations on all CPUs */
for (i = 0; i < CONFIG_SMP_NCPUS; i++)
{
timeslice = nxsched_cpu_scheduler(i, ticks, noswitches);
if (timeslice > 0 && timeslice < minslice)
{
minslice = timeslice;
}
}
leave_critical_section(flags);
return minslice < UINT32_MAX ? minslice : 0;
#else
/* Perform scheduler operations on the single CPUs */
return nxsched_cpu_scheduler(0, ticks, noswitches);
#endif
}
#else
# define nxsched_process_scheduler(t,n) (0)
#endif
sched_timer_resume重新評估下一個截止日期並重新啓動間隔計時器。
/****************************************************************************
* Name: sched_timer_resume
*
* Description:
* Re-assess the next deadline and restart the interval timer. This is
* called from wd_start() after it has inserted a new delay into the
* timer list.
*
* Input Parameters:
* None
*
* Returned Value:
* None.
*
* Assumptions:
* This function is called right after sched_timer_cancel(). If
* CONFIG_SCHED_TICKLESS_ALARM=y, then g_stop_time must be the value time
* when the timer was cancelled.
*
****************************************************************************/
void sched_timer_resume(void)
{
unsigned int nexttime;
#ifdef CONFIG_SCHED_SPORADIC
/* Save the last time that the scheduler ran */
(void)up_timer_gettime(&g_sched_time);
#endif
/* Reassess the next deadline (by simply processing a zero ticks expired)
* and set up the next interval (or not).
*/
nexttime = nxsched_timer_process(0, true);
nxsched_timer_start(nexttime);
}