I am trying to find out more information about how the RUN pin of the BCM is connected, and what circuitry is in place outside the BCM to connect up to the RUN jumper (i.e. for reset functionality).
What I am trying to do is to connect the RUN pin to the INT pin of a DS3231 RTC. The intention of this is to be able to set an alarm on the RTC prior to shutting down the Pi, which will allow the Pi to be rebooted at some time in the future.
The DS3231 requires that the INT pin (which is active low - i.e. it is pulled low for an alarm) have a pull-up. My understanding is that the RUN pin does already have a pull-up, so I am wondering if that pull-up is sufficient when connecting it to the DS3231. My experience however is that if I just connect the two pins, when the alarm activates while the Pi is booted, the Pi stops running, but does not boot - which seems to indicate that the RUN pin is not returning to a high state. I have not managed to do any investigation yet, and I was hoping I might be able to get some more insights into how the RUN pin is presented on the PUN jumper before I start trying to work out what is going on. I have also seen some mention somewhere of a capacitor being used as part of the reset circuit as well.
Any advice or pointers to documentation would be appreciated.