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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.

Seamus
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Damn Vegetables
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    Does this answer your question? [How should the J2 header be used on a raspberry pi 4?](https://raspberrypi.stackexchange.com/questions/108689/how-should-the-j2-header-be-used-on-a-raspberry-pi-4) – Milliways Jul 19 '20 at 00:06

2 Answers2

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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.

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.

Seamus
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    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
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    @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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PI4 SOM spec on global_EN

In the specifications of the Raspberry pi SOM (CM4) it clarify that you need to pull it down for more than 1ms to reboot and you need to turn off the OS before to run it

lavion jaune
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  • It might be very nice if you could put a **link** to the documentation/specifications you reference in your answer. – Seamus Mar 16 '21 at 21:40
  • This is NOT an Answer to the Question which was "Starting Pi 4 with global_en" – Milliways Mar 16 '21 at 23:24
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    If you look at the schematic onpenly accessible on kicad this come back to the same output and it's only to clarify the previous post. You can find here the full documentation of the SOM (https://datasheets.raspberrypi.org/cm4/cm4-datasheet.pdf). On the CM4IO board (motherboard for raspberry CM4) we can see an application with a clock powered by a battery triggering the CM4 module (processing power) for energy saving applications. If you're interested you can also find the datasheet for the IOBoard here (https://datasheets.raspberrypi.org/cm4io/cm4io-datasheet.pdf) – lavion jaune Mar 22 '21 at 16:44