diff options
Diffstat (limited to 'src/sched.c')
| -rw-r--r-- | src/sched.c | 38 |
1 files changed, 29 insertions, 9 deletions
diff --git a/src/sched.c b/src/sched.c index eb35bc8e..19e428be 100644 --- a/src/sched.c +++ b/src/sched.c @@ -19,21 +19,41 @@ static uint16_t millis; +static struct timer ms_timer, sentinel_timer; + // Default millisecond timer. This timer counts milliseconds. It -// also simplifies the timer code by ensuring there is always at least -// one timer on the timer list and that there is always a timer not -// more than 1 ms in the future. +// also simplifies the timer code by ensuring there is always a timer +// on the timer list and that there is always a timer not more than +// 1ms in the future. static uint_fast8_t ms_event(struct timer *t) { millis++; timer_periodic(); - t->waketime += sched_from_us(1000); + ms_timer.waketime += sched_from_us(1000); + sentinel_timer.waketime = ms_timer.waketime + 0x80000000; return SF_RESCHEDULE; } static struct timer ms_timer = { - .func = ms_event + .func = ms_event, + .next = &sentinel_timer, +}; + +// The sentinel timer is always the last timer on timer_list - its +// presence allows the code to avoid checking for NULL while +// traversing timer_list. Since sentinel_timer.waketime is always +// equal to (ms_timer.waketime + 0x80000000) any added timer must +// always have a waketime less than one of these two timers. +static uint_fast8_t +sentinel_event(struct timer *t) +{ + shutdown("sentinel timer called"); +} + +static struct timer sentinel_timer = { + .func = sentinel_event, + .waketime = 0x80000000, }; // Check if ready for a recurring periodic event @@ -91,7 +111,7 @@ sched_timer(struct timer *add) } else { // Find position in list and insert struct timer *pos = timer_list; - while (pos->next && !sched_is_before(waketime, pos->next->waketime)) + while (!sched_is_before(waketime, pos->next->waketime)) pos = pos->next; add->next = pos->next; pos->next = add; @@ -128,7 +148,7 @@ reschedule_timer(struct timer *t) { struct timer *pos = t->next; uint32_t minwaketime = t->waketime + 1; - if (!pos || !sched_is_before(pos->waketime, minwaketime)) + if (!sched_is_before(pos->waketime, minwaketime)) // Timer is still the first - no insertion needed return t; @@ -141,7 +161,7 @@ reschedule_timer(struct timer *t) // micro optimization for AVR - reduces register pressure asm("" : "+r"(prev) : : "memory"); pos = pos->next; - if (!pos || !sched_is_before(pos->waketime, minwaketime)) + if (!sched_is_before(pos->waketime, minwaketime)) break; } t->next = pos; @@ -180,7 +200,7 @@ static void timer_shutdown(void) { timer_list = &ms_timer; - ms_timer.next = NULL; + ms_timer.next = &sentinel_timer; timer_set_next(timer_list->waketime); } DECL_SHUTDOWN(timer_shutdown); |