esp-idf/components/esp_hw_support/port/esp32c2/Kconfig.rtc

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choice RTC_CLK_SRC
prompt "RTC clock source"
default RTC_CLK_SRC_INT_RC
help
Choose which clock is used as RTC clock source.
config RTC_CLK_SRC_INT_RC
bool "Internal 150kHz RC oscillator"
config RTC_CLK_SRC_EXT_OSC
bool "External 32kHz oscillator at 32K_XP pin"
config RTC_CLK_SRC_INT_8MD256
bool "Internal 8MHz oscillator, divided by 256 (~32kHz)"
endchoice
config RTC_CLK_CAL_CYCLES
int "Number of cycles for RTC_SLOW_CLK calibration"
default 3000 if RTC_CLK_SRC_EXT_OSC || RTC_CLK_SRC_INT_8MD256
default 1024 if RTC_CLK_SRC_INT_RC
range 0 27000 if RTC_CLK_SRC_EXT_OSC || RTC_CLK_SRC_INT_8MD256
range 0 32766 if RTC_CLK_SRC_INT_RC
help
When the startup code initializes RTC_SLOW_CLK, it can perform
calibration by comparing the RTC_SLOW_CLK frequency with main XTAL
frequency. This option sets the number of RTC_SLOW_CLK cycles measured
by the calibration routine. Higher numbers increase calibration
precision, which may be important for applications which spend a lot of
time in deep sleep. Lower numbers reduce startup time.
When this option is set to 0, clock calibration will not be performed at
startup, and approximate clock frequencies will be assumed:
- 150000 Hz if internal RC oscillator is used as clock source. For this use value 1024.
- 32768 Hz if the 32k crystal oscillator is used. For this use value 3000 or more.
In case more value will help improve the definition of the launch of the crystal.
If the crystal could not start, it will be switched to internal RC.