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esp_timer: don’t busy loop in esp_timer_impl_set_alarm

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Previously the loop in esp_timer_impl_set_alarm was necessary to catch
the case when timer count wraps around (goes from 2^32 - 1 to 0).
Since ALARM_OVERFLOW_VAL was reduced from 2^32 - 1 to 0xefffffff,
this is no longer necessary.

Fixes https://github.com/espressif/esp-idf/issues/1891
This commit is contained in:
Ivan Grokhotkov 2018-05-23 21:50:55 +08:00 committed by bot
parent 03c2678aa6
commit 125bbf0882
1 changed files with 8 additions and 16 deletions
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24
components/esp32/esp_timer_esp32.c
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@ -216,18 +216,6 @@ void IRAM_ATTR esp_timer_impl_set_alarm(uint64_t timestamp)
// Adjust current time if overflow has happened
bool overflow = timer_overflow_happened();
uint64_t cur_count = REG_READ(FRC_TIMER_COUNT_REG(1));
uint32_t offset = s_timer_ticks_per_us * 2; //remain 2us for more safe
//If overflow is going to happen in 1us, let's wait until it happens,
//else we think it will not happen before new alarm set.
//And we should wait current timer count less than ALARM_OVERFLOW_VAL,
//maybe equals to 0.
if (cur_count + offset >= ALARM_OVERFLOW_VAL) {
do {
overflow = timer_overflow_happened();
cur_count = REG_READ(FRC_TIMER_COUNT_REG(1));
} while(!overflow || cur_count == ALARM_OVERFLOW_VAL);
}
if (overflow) {
assert(time_after_timebase_us > s_timer_us_per_overflow);
@ -237,13 +225,17 @@ void IRAM_ATTR esp_timer_impl_set_alarm(uint64_t timestamp)
// Calculate desired timer compare value (may exceed 2^32-1)
uint64_t compare_val = time_after_timebase_us * s_timer_ticks_per_us;
uint32_t alarm_reg_val = ALARM_OVERFLOW_VAL;
// Use calculated alarm value if it is less than 2^32-1
// Use calculated alarm value if it is less than ALARM_OVERFLOW_VAL.
// Note that if by the time we update ALARM_REG, COUNT_REG value is higher,
// interrupt will not happen for another ALARM_OVERFLOW_VAL timer ticks,
// so need to check if alarm value is too close in the future (e.g. <2 us away).
const uint32_t offset = s_timer_ticks_per_us * 2;
if (compare_val < ALARM_OVERFLOW_VAL) {
// If we by the time we update ALARM_REG, COUNT_REG value is higher,
// interrupt will not happen for another 2^32 timer ticks, so need to
// check if alarm value is too close in the future (e.g. <1 us away).
if (compare_val < cur_count + offset) {
compare_val = cur_count + offset;
if (compare_val > ALARM_OVERFLOW_VAL) {
compare_val = ALARM_OVERFLOW_VAL;
}
}
alarm_reg_val = (uint32_t) compare_val;
}