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When I ran the command poweroff in ubuntu 19.10, I noticed that both the Ethernet port and USB ports remain powered even when the rbp4 seemed to have halted. Others using rasbian seem to have had similar experiences.

Which peripherals remain powered when the rbp4B is powered off? and where can I learn more about RBP4 power states? Are they documented somewhere?

Edit 1: I just skimmed over the Technical Reference Manual for ARM® Cortex®-A72 MPCore-based microprocessors (supposedly what the bcm2711 is based on). The manual discusses power modes but I couldn't find information on how peripherals like sdcard reader, usb, and ethernet are handled.

Does the BCM2711 have a manual for RBP4 users can access?

Update: Through testing, I can confirm that everything (including the microSD card reader's VDD pin) remain fully powered. It also seems that the fact of the system halting is not conveyed to peripherals in any way.

Tenders McChiken
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  • Who knows? Ubuntu uses its own kernel etc. NOT the official Foundation code. Despite its fixation with open source I don't know of any public code. Ask on a Ubuntu support site (if you can find one). – Milliways Feb 13 '20 at 08:41
  • Mind you if you are using Ubuntu Server (the only "supported" OS) why are you powering it off? – Milliways Feb 13 '20 at 08:42
  • @Milliways This same behavior was observed in Rasbian, so I don't think it's specific to Ubuntu. Should I edit ubuntu out of this question? – Tenders McChiken Feb 13 '20 at 08:45
  • If you ask a Question about Raspbian (don't know this Rasbian) and present some evidence you might get an Answer. All previous Pi models Pi models remained powered at all times - the Pi4 has power control capability but this was disabled (by default) in later firmware because some Luddites had designed hardware which assumed this. See [Raspberry Pi Power Limitations](https://raspberrypi.stackexchange.com/questions/51615/raspberry-pi-power-limitations) and https://raspberrypi.stackexchange.com/a/100234/8697 – Milliways Feb 13 '20 at 10:46

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This is most likely related to the bootloader settings. Setting POWER_OFF_ON_HALT=0 or WAKE_ON_GPIO=1 will keep the 3.3V line powered after a shutdown. The Ethernet chip is powered with 3.3V, so it will remain on indefinitely. You can see active bootloader settings in Rapsbian with vcgencmd bootloader_config.

This is not thoroughly documented anywhere as far as I know, but the single most important factor seems to be the 3.3V availability. If it's shut down, the power consumption is greatly reduced, but you cannot wake up your RPi with a GPIO and trying to reset your system in software will lead to a power-off. If it remains on, most of the board remains powered, consuming a significant amount of power.

Dmitry Grigoryev
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    Yep. i just tested my board and can confirm that all peripherals remain fully powered. A Raspberry Pi Foundation engineer even stated that the 5v rail cannot be turned off. – Tenders McChiken Feb 24 '20 at 08:55
  • @TendersMcChiken 5V rail is more or less directly connected to the power supply input. There aren't many things that are directly powered by 5V though. – Dmitry Grigoryev Feb 24 '20 at 08:59
  • I was under the assumption that USB ports were powered directly from the system's 5V rail. Am I mistaken? – Tenders McChiken Feb 24 '20 at 09:02
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    They are powered though a AP2552 overcurrent protection chip limiting the total USB current to 1.2A. – Dmitry Grigoryev Feb 24 '20 at 09:08