Re: Startup-/Shutdown Button for the Raspberry Pi 4

> On Jul 12, 2022, at 8:17 PM, Dr. Rolf Jansen - freebsd-rj at cyclaero.com <nxtzmchnyjrirskcrisaafakxcekosgmhdcricnnjyxomsvwpn@simplelogin.co> wrote:
> 
> 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:
>            ___ 
>             | /
>             |/
>             /
>            /
>         +-o      o--------+
>         |        |        |
>         |       [R] 100 Ω |
>         |        |        |
>         o        o        o
>       Pin 5    Pin 6    Pin 13
>      (SCL 1)   (GND)   (GPIO 27)

Ok, I’ll bite. I’m not understanding this.

I imagine that the resistor is a current limit for the gpio pin and not the pullup.

Regardless of how it is wired, why use SCL1 which is pulsing? And how can any of this cause a boot?

Is this “magic” dependent on some quirk(s) of RPi? Will it work with others, like Rock64?

> 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]  
>    -p file    the path to the pid file [default: /var/run/shutdd.pid]  
>    -f         foreground mode, don't fork off as a daemon.  
>    -n         no console, don't fork off as a daemon.  
>    -b         GPIO bank id [default: 0].  
>    -g         GPIO line id [default: 27].  
>    -h         shows these usage instructions.  
> 
>   echo "/usr/local/bin/shutdd" >> /etc/rc.local 
> 
> 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.
> 
> 
>