The posts I found online show conflicting information on how the J2 header should be used, and seem to be derived from trial and error. None of the answers I managed to find seem authoritative; i.e. given by engineers at the Raspberry Pi Foundation or sourced from component documentation.
The only information I was able to confirm is that
- Power for the RBP4 is managed by the MXL7704 PMIC.
- The state of the PMIC can be controlled by the J2 header.
- The RBP4 is designed to to start up after being halted.
Given this information, I would like to have answers for the following questions:
- What is the proper way to power on (i.e. turn on) a halted RBP4 using the J2 header?
- What is the proper way to reset power using the J2 header?
Definitive answers to both questions would help me and, evidently, many other people.
Update: From a Raspberry Pi engineer, the answers to the questions are as follows:
- Momentarily short GLOBAL_EN to ground to restart a halted RBP4.
- Momentarily short GLOBAL_EN to ground to restart a running RBP4. Usual caveats about suddenly powering off your system apply.