STM32G070RB, Maximum Alarm length

[MEder]

What is the maximum alarm length in the G070. I only see about 30days.

I need 6 months.

I guess I could implement one using the TAMP_BKPxR registers and compare the RTC DR , TR with the alarm values I have store in the TAMP regs. ( stripping out the WDU)

I only need to check the alarm on start up.

Thanks

[Uwe Bonnes]

Set alarm to the longest time possible, wake up and check if you have to delay for another step or if you wake up for the real event.

[waclawek.jan]

You can also run the RTC with a higher divider, i.e. not at the nominal speed but slower.

JW

[MEder]

I am using the RTC for time stamps to a log, so I can't change the clock. I could set a 24hr alarm and check for the 6 month period, but I just need to check on startup, it'll be on/off multiple times a day.

So the RTC DR and TR regs are formatted such that his will work...

My Alarm date is stored in 2 TAMP regs in the same format as the DR and TR regs.

// read TAMP regs 0 & 1 and see if the alarm time has passed.

uint32_t alarm_timereg = BACKUP_TR_REG; // TAMP_BKP0R

uint32_t alarm_datereg = BACKUP_DR_REG; // TAMP_BKP1R

// read out both to prevent lock

uint32_t trreg = RTC->TR;

uint32_t drreg = RTC->DR & ~RTC_DR_WDU_Msk; // remove Weekdays

// Check Enable bit

if(alarm_timereg & ALARMX_ENABLE){ // strip enable bit from TAMP reg to check alarm, I store the alarm enable in the TAMP reg

alarm_timereg &= ~ALARMX_ENABLE;

if(drreg >= alarm_datereg){ // format of time reg is PM, H,M,S, date reg is Y,M,D

if(trreg >= alarm_timereg){

return(1); // Alarm date has passed

}

}

} // end if enabled

return (0);

Seems to work ok, even for 12 hour am/pm settings.