STM32_RTC_PRER_PRED_A
prer &= STM32_RTC_PRER_PRED_S | STM32_RTC_PRER_PRED_A;
STM32_RTC_PRER_PRED_A;
pred_a_max = STM32_RTC_PRER_PRED_A >> STM32_RTC_PRER_PRED_A_SHIFT;