1choice RTC_CLK_SRC 2 prompt "RTC clock source" 3 default RTC_CLK_SRC_INT_RC 4 help 5 Choose which clock is used as RTC clock source. 6 7 config RTC_CLK_SRC_INT_RC 8 bool "Internal 136kHz RC oscillator" 9 config RTC_CLK_SRC_EXT_OSC 10 bool "External 32kHz oscillator at pin0" 11 config RTC_CLK_SRC_INT_8MD256 12 bool "Internal 17.5MHz oscillator, divided by 256" 13endchoice 14 15config RTC_CLK_CAL_CYCLES 16 int "Number of cycles for RTC_SLOW_CLK calibration" 17 default 3000 if RTC_CLK_SRC_EXT_OSC || RTC_CLK_SRC_INT_8MD256 18 default 1024 if RTC_CLK_SRC_INT_RC 19 range 0 8190 if RTC_CLK_SRC_EXT_OSC || RTC_CLK_SRC_INT_8MD256 20 range 0 32766 if RTC_CLK_SRC_INT_RC 21 help 22 When the startup code initializes RTC_SLOW_CLK, it can perform 23 calibration by comparing the RTC_SLOW_CLK frequency with main XTAL 24 frequency. This option sets the number of RTC_SLOW_CLK cycles measured 25 by the calibration routine. Higher numbers increase calibration 26 precision, which may be important for applications which spend a lot of 27 time in deep sleep. Lower numbers reduce startup time. 28 29 When this option is set to 0, clock calibration will not be performed at 30 startup, and approximate clock frequencies will be assumed: 31 32 - 150000 Hz if internal RC oscillator is used as clock source. For this use value 1024. 33 - 32768 Hz if the 32k crystal oscillator is used. For this use value 3000 or more. 34 In case more value will help improve the definition of the launch of the crystal. 35 If the crystal could not start, it will be switched to internal RC. 36