7

It seems that those pins can be used to start Pi 4, but I am not sure exactly how. Can a Pi 4 start after having been shut down by the shutdown menu, if I connect the two holes like below for a short moment?

For what it's worth, I have set the following configurations to reduce power usage when it is shut down.

BOOT_UART = 0
WAKE_ON_GPIO = 0
POWER_OFF_ON_HALT = 1

connect


PS: It does. I was afraid to try it because it might burn my Pi, but since no one was answering, I took the risk. I connected the 2 holes with an M-M jumper cable for a second, and the green LED began to blink and the Pi 4 booted.

5

The Organization's schematic is incomplete, but it does show GLOBAL_EN connected to U2 - the PMIC (Power Management Integrated Circuit). Pulling GLOBAL_EN low (aka shorting to GND) resets the PMIC - which causes it to power up all its outputs, in turn causing the Pi 4 to boot - it's exactly the same as when you disconnect power, then re-connect it.

Your question is not completely clear to me, but when you say, "I am not sure exactly how" you may be asking, "How would one implement this feature - shorting GLOBAL_EN to GND?" If that's part of your question, there are several ways this could be done, but I know of nothing in the current Pi 4 hardware that would support this. One typical way this is done on other machines is with a RTC (Real Time Clock), but Pis have never had one. Another way would be with an external sensor of some type that provided a switch closure when some condition was sensed. Still another way would be to use a small microcontroller (Arduino for example) to set the state of GLOBAL_EN.

The documentation states:

POWER_OFF_ON_HALT

If 1 and WAKE_ON_GPIO=0 then switch off all PMIC outputs in halt. This is lowest possible power state for halt but may cause problems with some HATs because 5V will still be on. GLOBAL_EN must be shorted to ground to boot.

Default: 0 Version: 2019-07-15

If you've not seen it, you might want to read this answer, or if you want full details try this GitHub page.. Now we've both confirmed shorting GLOBAL_EN to GND will in fact boot the RPi 4 from halt, poweroff or shutdown when the EEPROM firmware is configured iaw the documentation.

  • 1
    If I'm using another uC to wake up the Pi via an NPN transistor, for how long do I need to pull it low? Does it make any difference if it stays low for a prolonged period of say a few seconds? – php_nub_qq Nov 23 '20 at 16:10
  • 1
    @php_nub_qq: I've not tested this myself, and AFAIK it's not documented. I do know it need be only very brief (a msec or less will do IIRC), but if it's leading edge triggered, then it son't actually re-start until you let it go high again. Please let us know what you learn - this is potentially useful information. Thanks! – Seamus Nov 23 '20 at 20:20

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