How to synchronize two RTC?

[suads]

Hi I have two custom boards with stm32wb55 with a external crystal oscillator for the rtc. One device should be the master and the other is the slave. Master should set the rtc for the slave. Is it possible to sync them over ble with a precision of 1 ms? My other option is nfc, to exchange the data between them, to set the rtc.

What is the best way to sync this two devices?

Thanks

[waclawek.jan]

Generally it's a two-step process. First, transfer date and time (content of DR and TR registers) in the usual RTC initialization.

Then, finish INIT, transfer subseconds, and perform the synchronization using RTC_SHIFTR register, as described in the RTC synchronization subchapter in RM.

JW