STM32F4 RTC with msec resolution and getter and setter function

Simple ZephyrOS device driver using RTC as system/sample clock. This clock can be set and read.

Setup: The driver uses the LSE as clock source and assumes that it is connected to an 32768Hz oscilator.

With the current pre-divers setup the sub second resolutions is around 4ms. The miliseconds are calculated according to the datasheet.

note: The time stamping function of the stm32 rtc is not used. Means that if the ZephyrOS switches the context inside "stm32_rtc_getTimestamp" function, the result in ss, t, d can have some offset.

sources:

• stm32f412 datasheet(RM0402)
• stm32HAL LL documentation (UM1725)