Real-Time Clock (RTC)

The Real-Time Clock (RTC) provides:

• Continuous timekeeping, even during system off and on states.
• Timestamp-based logging and event scheduling.
• Alarm functionality to wake the system from sleep (Work in Progress; Zephyr driver support expected from version 4.0).

Integration Details

• The RTC module requires configuration, initialization, and software functions to access the hardware.
• Integrated with Zephyr RTOS using Zephyr's device driver model and APIs for the STM32 RTC module.

Useful Links

• Zephyr RTC API documentation
• STM32 RTC documentation

Considerations

Warning

RTC should be available / running if Low-Speed-External Clock (LSE) is configured in Standby and Shutdown State of the STM32.

• Shutoff does not work
• Standby works -> current configuration

Warning

Precision of RTC Time is low.

• LSE clock should be precise as +- 10 ppm, but RTC time is off like 10000 ppm

Warning

RTC write has offset (e.g. read after write gives + 50 years, + 10 hours, or similar).

• Fixed integrated by storage of the offset after write into flash. Time read will apply the offset by software

Warning

Enabling RTC increases power usage.

• Measurement: 37 µA of whole BMS during standby state with RTC active (logged on 25/08/2025) -> in range for the BMS energy storage limit