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drivers: timer: nrf_rtc_timer: avoid starving clock announcements

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When setting a timeout measure the number of accumulated unannounced
ticks.  If this value exceeds half the 24-bit cycle counter range
force an announcement so the unannounced cycles are incorporated into
the system tick counter.

Signed-off-by: Peter Bigot <peter.bigot@nordicsemi.no>
This commit is contained in:
Peter Bigot 2019-11-23 16:36:51 -06:00 • committed by Carles Cufí
commit fd5b502b64
1 changed files with 14 additions and 2 deletions
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16
drivers/timer/nrf_rtc_timer.c
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@ -15,7 +15,9 @@
#define RTC NRF_RTC1
#define COUNTER_MAX 0x00ffffff
#define COUNTER_SPAN BIT(24)
#define COUNTER_MAX (COUNTER_SPAN - 1U)
#define COUNTER_HALF_SPAN (COUNTER_SPAN / 2U)
#define CYC_PER_TICK (sys_clock_hw_cycles_per_sec() \
/ CONFIG_SYS_CLOCK_TICKS_PER_SEC)
#define MAX_TICKS ((COUNTER_MAX - CYC_PER_TICK) / CYC_PER_TICK)
@ -120,12 +122,22 @@ void z_clock_set_timeout(s32_t ticks, bool idle)
k_spinlock_key_t key = k_spin_lock(&lock);
u32_t cyc, dt, t = counter();
u32_t unannounced = counter_sub(t, last_count);
bool zli_fixup = IS_ENABLED(CONFIG_ZERO_LATENCY_IRQS);
/* If we haven't announced for more than half the 24-bit wrap
* duration, then force an announce to avoid loss of a wrap
* event. This can happen if new timeouts keep being set
* before the existing one triggers the interrupt.
*/
if (unannounced >= COUNTER_HALF_SPAN) {
ticks = 0;
}
/* Get the cycles from last_count to the tick boundary after
* the requested ticks have passed starting now.
*/
cyc = ticks * CYC_PER_TICK + 1 + counter_sub(t, last_count);
cyc = ticks * CYC_PER_TICK + 1 + unannounced;
cyc += (CYC_PER_TICK - 1);
cyc = (cyc / CYC_PER_TICK) * CYC_PER_TICK;