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sched: Avoid rescheduling the currently active timer

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It's tricky to reschedule the timer irq correctly (due to race
conditions with the irq) and in practice it's very rarely needed.
Handle the special cases in the generic sched.c code so that the board
code doesn't have to handle it.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
This commit is contained in:
Kevin O'Connor 2017-03-10 20:03:56 -05:00
parent cb286ede9d
commit 0a3c23bcf6
5 changed files with 53 additions and 90 deletions
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42
src/avr/timer.c
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@ -38,13 +38,6 @@ timer_set(uint16_t next)
OCR1A = next;
}
static inline void
timer_set_clear(uint16_t next)
{
OCR1A = next;
TIFR1 = 1<<OCF1A;
}
static inline void
timer_repeat_set(uint16_t next)
{
@ -78,6 +71,15 @@ timer_init(void)
}
DECL_INIT(timer_init);
static void
timer_shutdown(void)
{
// Reenable timer irq
timer_set(timer_get() + 50);
TIFR1 = 1<<OCF1A;
}
DECL_SHUTDOWN(timer_shutdown);
/****************************************************************
* 32bit timer wrappers
@ -120,35 +122,15 @@ timer_periodic(void)
}
}
#define TIMER_MIN_TICKS 100
// Set the next timer wake time (in absolute clock ticks). Caller
// must disable irqs. The caller should not schedule a time more than
// a few milliseconds in the future.
uint8_t
timer_set_next(uint32_t next)
{
uint32_t cur = timer_read_time();
if ((int16_t)(OCR1A - (uint16_t)cur) < 0 && !(TIFR1 & (1<<OCF1A)))
// Already processing timer irqs
try_shutdown("timer_set_next called during timer dispatch");
uint32_t mintime = cur + TIMER_MIN_TICKS;
if (sched_is_before(mintime, next)) {
timer_set_clear(next);
return 0;
}
timer_set_clear(mintime);
return 1;
}
#define TIMER_IDLE_REPEAT_TICKS 8000
#define TIMER_REPEAT_TICKS 3000
#define TIMER_MIN_TRY_TICKS 60 // 40 ticks to exit irq; 20 ticks of progress
#define TIMER_DEFER_REPEAT_TICKS 200
// Similar to timer_set_next(), but wait for the given time if it is
// in the near future.
// Set the next timer wake time (in absolute clock ticks) or return 1
// if the next timer is too close to schedule. Caller must disable
// irqs.
uint8_t
timer_try_set_next(uint32_t target)
{