I have previously seen inside the Raspberry Pi device tree (DT) overlay information on how to wire up a power button for a Raspberry Pi. Now that I am about to use a Raspberry Pi as a desktop PC replacement, I have a more immediate need for an actual power button. So I thought I better do some additional web searching and write an actual blog article with the information on how to do this.
A cursory search brings up an article about how to create a Raspberry
Pi power button without the use of the device tree (DT) overlay.
After a little bit more searching, it looks like this is the “old
technique” as the necessary device tree overlay, gpio-shutdown, did
not exist in earlier versions of Raspbian before Debian Stretch.
20191123/DuckDuckGo raspberry pi power button
20191123/https://howchoo.com/g/mwnlytk3zmm/how-to-add-a-power-button-to-your-raspberry-pi
That being said, it is my preference to use the device tree (DT) overlay version instead because I think it is simply a cleaner way to solve the same problem.
20191124/DuckDuckGo raspberry pi power button overlay
20191124/DuckDuckGo gpio-shutdown overlay
20191124/https://raspberrypi.stackexchange.com/questions/77905/raspberry-pi-3-model-b-dtoverlay-gpio-shutdown
20191124/https://www.stderr.nl/Blog/Hardware/RaspberryPi/PowerButton.html
20191124/https://github.com/raspberrypi/firmware/blob/master/boot/overlays/README
Also noteworthy is the gpio-poweroff overlay. This is an overlay
meant to provide additional support for external power devices so that
when the Raspberry Pi computer board shuts down, it can also send a
signal to the power controller to cut off power to the Raspberry Pi
board (and maybe also larger system) completely, rather than simply
having the Raspberry Pi board idle in the halted state.
Also interesting, from the last link, is mention of the gpio-keys
device tree (DT) overlay. This one allows you to generate arbitrary
key input events when a GPIO button is pushed. Indeed, a much cleaner
way to implement than a daemon that polls the GPIO event states, and
this likewise allows you to effortlessly take advantage of the the
ability to generate interrupts when a GPIO event occurs, since we have
the required kernel mode code running to intercept the interrupts.
Again, gpio-keys was not available in the older versions of Raspbian
before Debian Stretch, so here again is an occurrence of “new way
versus old way.” Yeah, too bad they couldn’t get that feature rolled
out earlier in time.