Using RTC on STM32l4 as a fail safe monthly wake up?

[Audrey Hendon]

Wondering if the STM32l4 RTC could be used to wake the processor from standby mode after 1 month.

Powered by the LSI, would the time drift beyond usability? Ie. It does not matter if the device wakes up 30 days or 31 days later. Just as long as its in the "ballpark".

Is a 30 day wakeup interval supported?

Thanks in advance!

[Jack Peacock_2 · Accepted solution]

You can configure the RTC alarm to trigger on a specific day of the month for a monthly wakeup. Accuracy depends on using LSE or LSI oscillator for the RTCCLK. For LSI there is a cumulative error which will become significant over a long period. You can reduce the error by calibrating the LSI. For LSE with a low PPM crystal cumulative error is less of a problem.

Jack Peacock

[berendi]

You can find the worst case LSI frequencies in the datasheet.

Does your definition of ballpark include 2 days earlier or 2.5 days later?

[waclawek.jan]

That's actually not bad at all, LSIs in other STM32 families tend to spread over tens of %.

JW

[Audrey Hendon]

Thanks for the responses! This helps a lot