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As mentioned in a comment to https://raspberrypi.stackexchange.com/a/19701/8697 and also in a few other places on this Forum "when the pi is shut down, pulling pin 5 low will make it boot up again"

I can find no reference to this supposed behaviour, although holding this pin low was supposed to boot in safe mode in older versions of Raspbian.

Indeed it does not work on my Pi Model B Revision 2. I can find no mechanism by which it could possibly work. The P6 connector makes the reset function accessible.

Have those proposing this tested this behaviour?

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1 Answers1

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When the pi is halted using sudo halt or similar, pulling pin 5 low will make it boot up again.

This is implemented in bootcode.bin as documented
http://elinux.org/RPI_safe_mode#Wake_from_Halt.5B1.5D

NOTE This will not reboot the Pi if the power has been interrupted.

The original Pi4 put the MxL7704 power management chip into a low power state when off - turning off the 3.3V supply and effectively totally shutting down the SoC. (I verified this by measuring the current.)
Unfortunately due to lobbying by a lot of luddites who had designed HATs that assumed 3.3V power was always available the EPROM is now configured by default to enable the MXL7704 PMIC when shut down. So you can now reboot by pulling pin 5 low.
It is possible to change this behaviour by modifying the Pi4 EEPROM. See Pi 4 Bootloader Configuration.

A reset button can be attached to the P6 header on Pi Model B Revision 2, which performs a similar reboot, and also works if the power has been interrupted.

EDIT The B+ and A+ have a Run header to reboot.

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