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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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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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