RTC Alarm Interrupts

I’m working on a project that I would like to trigger an event from the RTC each second.

With some initial guidance from @ScruffR, he pointed me to the datasheet:


and some Particle code using the RTC timers for sleep/wake.

I’m not sure how to peel back the layers to access the registers for AlarmB (Particle seems to only use Alarm A) and define an interrupt vector to execute my code.

I know @rickkas7 may hold the keys to this but any guidance would be appreciated.