Two module clocks, 19.2 MHz (CLK_19P2M) and 32.768 kHz (PMIC_SLPCLK_1) are routed out through the board-to-board connectors for use on expansion boards.
RTC backup battery
A backup power source is required for the RTC to operate robustly by preventing RTC data losses during unexpected power events. Implementation options are provided in Real-time Clock Backup Battery in the Expansion Board Design Guide.
The most common solution is a non-rechargeable coin-cell battery connected to V_RTC at module connector J6, pin 11.