I found a following description in RM page 37.
"The OSC32k runs from VDD_SNVS_CAP, which comes from the VDD_HIGH_IN/VDD_SNVS_IN power mux. The target battery is a ~3 V coin cell."
From "Table 6. Operating Ranges", VDD_SNVS_IN is from 2.8V to 3.3V.
However in "Table 21. XTALI and RTC_XTALI DC Parameters", 32KHz RTC_XTALI Vih max is 1.1V.
How should I consider the voltage for RTC_XTALI?