After wasting a lot of time trying to figure out why periodic timer interrupts work at some but not all “Timer Clock Frequency”, i finally decided to dig into the RAK recommended library i was using.
In doing so, i found a posted issue for setting the bits for different periodic timer “Timer Clock Frequency” options. This issue hasnt been merged in over a year. I solved my first issue
I suspect the author wrote/tested the library without a backup power on the RTC. In my case, unless the super cap drained, some settings would revert to defaults so i could get the right settings again!
Looking further, i saw @beegee, posted in repo he had wasted time on similar problem with the EEPROM functionality of the RTC.
I also had problems with alarm interrupts firing instantly when the first alam was set. Datasheet clearly shows how to avoid this, but library uses the flawed same scheme of bit manipulation which fails here also.
Just a warning to others… Lots of issues with this library!
Hopefully in the new year ill be able to post a fork that works better.