STM32_RTC_PRER_PRED_S
prer &= STM32_RTC_PRER_PRED_S | STM32_RTC_PRER_PRED_A;
STM32_RTC_PRER_PRED_S;
pred_s_max = STM32_RTC_PRER_PRED_S >> STM32_RTC_PRER_PRED_S_SHIFT;