RTC Calibration question

[JimTal001]

Is there a way to make the RTC calibration value persist through power cycles with VBAT un-powered.?

Now that I have a determined my pyboard RTC needs to be adjusted by a value of -129, what is the best way to apply this adjustment?
I was under the impression that once the correction was applied via: rtc.calibration(-129) it would persist through power cycles with VBAT un-powered, I was wrong.

Maybe the only solution is to add the following lines to boot.py:

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rtc=pyb.RTC()
rtc.calibration(-129)

[blmorris]

I think you have the right answer. Without power or VBAT you only retain what you have stored in flash (or the SD card). Everything else - RTC time, backup RAM and backup registers - is lost. The RTC calibration register is just another RAM address, albeit one that implements a specific write protection method and is backed up by VBAT.
Other than that, are you finding that the RTC calibration lets you lock in the precision you need?
-Bryan

[JimTal001]

Thanks Bryan,

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Other than that, are you finding that the RTC calibration lets you lock in the precision you need?

So far so good.