Date: Tue, 12 Jul 2022 22:17:00 -0300 From: "Dr. Rolf Jansen" <freebsd-rj@cyclaero.com> To: freebsd-arm <freebsd-arm@freebsd.org> Subject: Startup-/Shutdown Button for the Raspberry Pi 4 Message-ID: <E1F8EA20-D709-45FD-941F-DB28921601D1@cyclaero.com>
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One week ago I started with exploring the Raspberry Pi 4 B, which might =
be a substitute for the aging BeagleBone Blacks for my future projects.
I very much like the built-in power button facility of the BBB, and =
unfortunately the RPi 4 has nothing comparable - the one button to rule =
it all.
I read a lot of howtos and blog posts (mostly for Linux) and nothing was =
really worth to give it even a try, compared to live without the button. =
Well, this is not becoming an elaborated question, but here I am going =
to elaborate my solution for FreeBSD.
1. I Prepared a momentary push button for connecting it to the RPi:
___=20
| /
|/
/
/
+-o o--------+
| | |
| [R] 100 =CE=A9 |
| | |
o o o
Pin 5 Pin 6 Pin 13
(SCL 1) (GND) (GPIO 27)
2. I created a shutdown daemon in C for FreeBSD, lurking for push button
events on a GPIO port: https://github.com/cyclaero/shutdd
clang -g0 -O3 -fsigned-char -Wno-empty-body -Wno-parentheses shutdd.c =
-lgpio -s -o /usr/local/bin/shutdd
shutdd [-p file] [-f] [-n] [-b] [-g] [-h] =20
-p file the path to the pid file [default: /var/run/shutdd.pid] =20=
-f foreground mode, don't fork off as a daemon. =20
-n no console, don't fork off as a daemon. =20
-b GPIO bank id [default: 0]. =20
-g GPIO line id [default: 27]. =20
-h shows these usage instructions. =20
echo "/usr/local/bin/shutdd" >> /etc/rc.local=20
Restart and ready for testing the RPi's Power Button.
shutdd does not poll the state of the GPIO port, but instead utilizes =
FreeBSD's user space interface for GPIO interrupts for lurking on state =
changes of the GPIO line - default GPIO.0.27. Therefore, no significant =
load is imposed on the CPU's.
After 2 hs of operation, in output of ps -ax:
...
550 - Is 0:00.03 /usr/local/bin/shutdd
...
- No CPU load !!!
- Pressing the power button does the same as shutdown -p now
- Pressing the power button when the RPi is down but still connected to =
the 5 V power supply lets it starting up.
BTW, I left the RTC DS3231 on I2C 1. That means, the RTC and the power =
button share the same pins for SCL 1 and GND.
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