21.5.3 Clocks

The RTC bus clock (CLK_RTC_APB) can be enabled and disabled in the power manager, and the default state of CLK_RTC_APB can be found in the Peripheral Clock Masking section of the MCLK – Main Clock chapter.

A 32.768 kHz or 1.024 kHz oscillator clock (CLK_RTC_OSC) is required to clock the RTC. This clock must be configured and enabled in the 32.768 kHz Oscillators Controller section before using the RTC.

CLK_RTC_OSC is asynchronous to CLK_RTC_APB. Due to this asynchronicity, writes to certain registers require synchronization between the clock domains.