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esp_timer: lock-free implementation of esp_timer_get_time

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The implementation of esp_timer_get_time used a critical section, which
resulted in a call time of ~1.8us. To make esp_timer_get_time more
useable as a high-resolution time source, this change replaces the lock
with polling. Call time is reduced to ~0.7us.
This commit is contained in:
Ivan Grokhotkov
2017-08-30 08:43:02 +08:00
parent c743bdac88
commit 1af6384349
2 changed files with 76 additions and 9 deletions
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38
components/esp32/esp_timer_esp32.c
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@@ -126,15 +126,35 @@ static inline bool IRAM_ATTR timer_overflow_happened()
uint64_t IRAM_ATTR esp_timer_impl_get_time()
{
portENTER_CRITICAL(&s_time_update_lock);
uint32_t timer_val = REG_READ(FRC_TIMER_COUNT_REG(1));
uint64_t result = s_time_base_us;
if (timer_overflow_happened()) {
result += s_timer_us_per_overflow;
}
uint32_t ticks_per_us = s_timer_ticks_per_us;
portEXIT_CRITICAL(&s_time_update_lock);
return result + timer_val / ticks_per_us;
uint32_t timer_val;
uint64_t time_base;
uint32_t ticks_per_us;
bool overflow;
uint64_t us_per_overflow;
do {
/* Read all values needed to calculate current time */
timer_val = REG_READ(FRC_TIMER_COUNT_REG(1));
time_base = s_time_base_us;
overflow = timer_overflow_happened();
ticks_per_us = s_timer_ticks_per_us;
us_per_overflow = s_timer_us_per_overflow;
/* Read them again and compare */
if (REG_READ(FRC_TIMER_COUNT_REG(1)) > timer_val &&
time_base == *((volatile uint64_t*) &s_time_base_us) &&
ticks_per_us == *((volatile uint32_t*) &s_timer_ticks_per_us) &&
overflow == timer_overflow_happened()) {
break;
}
/* If any value has changed (other than the counter increasing), read again */
} while(true);
uint64_t result = time_base
+ (overflow ? us_per_overflow : 0)
+ timer_val / ticks_per_us;
return result;
}
void IRAM_ATTR esp_timer_impl_set_alarm(uint64_t timestamp)