Strange behaviour of RTC / RTCZero library

I'm using the Adafruit Feather M0 board which has the same chip as the Zero the SAMD21

When I run the RTC / RTCZero examples on the Feather M0 I get some strange behavior

12:00:00 rolls over to 28:00:00 ! 28:59:59 then eventaually rolls to 17:00:00 ! Which then runs correctly until 23:59:59

If you set the RTC to 23:59:59 it rolls over to 24:00:00 and does not increment the day/date.

Can anyone confirm that a vanilla Zero boards work correctly or has the same issues. It would help me narrow down whether its a board specific issue or the library.

I have tried versions 1.2.0 and 1.3.0 of the RTCZero Library and just the SimpleRTC example

Cheers Jon

I can confirm the issue on my Zero.

This reminds me of an issue I ran into with the Intersil ISL12022MA RTC... The hour register has a bit to indicate AM / PM. I wonder if this is the same type of issue?

Turns out there was an issue with the RTCZero library and the fact it wasn't setting the 24Hr mode correctly.

There is a forked library at which works correctly and a pull request in.

So hopefully the main trunk will be corrected to.