Programmable Alarms; Periodic Auto-Wakeup - ST STM32G0 1 Series Reference Manual

Real-time clock (RTC)
BYPSHAD control bit in the RTC_CR register. By default, this bit is cleared, and the user
accesses the shadow registers.
When reading the RTC_SSR, RTC_TR or RTC_DR registers in BYPSHAD = 0 mode, the
frequency of the APB clock (f
(f
RTCCLK
The shadow registers are reset by system reset.
30.3.6

Programmable alarms

The RTC unit provides programmable alarm: alarm A and alarm B. The description below is
given for alarm A, but can be translated in the same way for alarm B.
The programmable alarm function is enabled through the ALRAE bit in the RTC_CR
register.
The ALRAF is set to 1 if the calendar subseconds, seconds, minutes, hours, date or day
match the values programmed in the alarm registers RTC_ALRMASSR and
RTC_ALRMAR. Each calendar field can be independently selected through the MSKx bits
of the RTC_ALRMAR register, and through the MASKSSx bits of the RTC_ALRMASSR
register.
The alarm interrupt is enabled through the ALRAIE bit in the RTC_CR register.
Caution: If the seconds field is selected (MSK1 bit reset in RTC_ALRMAR), the synchronous
prescaler division factor set in the RTC_PRER register must be at least 3 to ensure correct
behavior.
Alarm A and alarm B (if enabled by bits OSEL[1:0] in RTC_CR register) can be routed to the
TAMPALRM output. TAMPALRM output polarity can be configured through bit POL the
RTC_CR register.
30.3.7

Periodic auto-wakeup

The periodic wakeup flag is generated by a 16-bit programmable auto-reload down-counter.
The wakeup timer range can be extended to 17 bits.
The wakeup function is enabled through the WUTE bit in the RTC_CR register.
The wakeup timer clock input ck_wut can be:
•
RTC clock (RTCCLK) divided by 2, 4, 8, or 16.
When RTCCLK is LSE (32.768 kHz), this allows to configure the wakeup interrupt
period from 122 µs to 32 s, with a resolution down to 61 µs.
•
ck_spre (usually 1 Hz internal clock)
When ck_spre frequency is 1 Hz, this allows to achieve a wakeup time from 1 s to
around 36 hours with one-second resolution. This large programmable time range is
divided in 2 parts:
–
–
880/1390
APB
).
from 1 s to 18 hours when WUCKSEL [2:1] = 10
and from around 18 h to 36 h when WUCKSEL[2:1] = 11. In this last case 2
added to the 16-bit counter current value. When the initialization sequence is
complete (see Programming the wakeup timer on page
counting down. When the wakeup function is enabled, the down-counting remains
active in low-power modes. In addition, when it reaches 0, the WUTF flag is set in
) must be at least 7 times the frequency of the RTC clock
RM0444 Rev 5
RM0444
16
882), the timer starts
is