1. ref_clock used in unit tests occasionally produces time off by ~100
microseconds shortly after being started. Add a delay to let
ref_clock stabilise, until the cause is found.
2. Reduce roundoff error accumulation which would occasionally cause
the test to fail, by choosing an overflow value which can be divided
by APB frequency.
3. Move time sampling part of the test into an IRAM function to
reduce variations due to cache behavior.
4. Remove calculation of "standard deviation" in the test, as what was
calculated was not actually standard deviation, and it did not add any
useful information.
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
When light sleep is started, the other CPU gets halted using DPORT
stall mechanism. This can happen while it is inside an esp_timer
critical section, which may lead to a deadlock. This change adds
functions to take and release esp_timer lock before entering
DPORT critical section, preventing the deadlock.
Moves the ets_timer_arm() / ets_timer_disarm() code paths to RAM
Overhead is 740 bytes of IRAM, 0 bytes DRAM
(For comparison: If all of esp_timer.c is moved to RAM, overhead is 1068 bytes IRAM and 480 bytes DRAM.)
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.
