How to: Exit emulator to emulationstation using GPIO button

[matthewjosephcordova]

I’ve came up with a method to be able to have an external pushbutton that is used to exit an emulator back to emulationstation. The way it works is by either sending a sigterm signal to the emulator, and if that doesn’t work, to try simulating a keypress (ESC). Some emulators don’t accept keypress from python’s uinput, so sigterm must be used. Some emulators don’t accept sigterm, so uinput must be used.

This is a python script, and uinput must be installed. You can test if uinput is properly installed by going to a command prompt and typing in
python
Then when you are in python idle,
import uinput
If it comes back with >>> , everything is working fine. If it says ImportError: No module named uinput, then it isn’t installed. On my image I downloaded from here, uinput was not installed correctly. To install uinput, try

pip install python-uinput
If that doesn’t work, try
easy_install python-uinput

RPi.GPIO must also be installed. In a command window, try
sudo apt-get install python-dev python-rpi.gpio

Now the script must be created. Save the following script as exit.py in /home/pi/

from time import sleep
import os
import RPi.GPIO as GPIO
import uinput

key_events=( uinput.KEY_ESC, )
device=uinput.Device(key_events)
GPIO.setmode(GPIO.BCM)
GPIO.setup(3, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)

def exitEmulator(channel):
    print('exitEmulator')
    pids = [pid for pid in os.listdir('/proc') if pid.isdigit()]

    for pid in pids:
        try:
            commandpath = open(os.path.join('/proc', pid, 'cmdline'), 'rb').read()
            if commandpath[0:24] == '/opt/retropie/emulators/':
                os.system('kill -TERM %s' % pid)
                print('kill -TERM %s' % pid)
                device.emit(uinput.KEY_ESC,1)
                sleep(2)
                device.emit(uinput.KEY_ESC,0)
        except IOError:
            continue
GPIO.add_event_detect(3, GPIO.RISING, callback=exitEmulator, bouncetime=500)

while True:
    sleep(10)

Now create another file, exit.sh in /home/pi/

#!/bin/sh

cd /
cd /home/pi
sudo python exit.py
cd /

Now, cron must be edited. Enter in a command terminal,
sudo crontab -e
Add the following line to the end,
@reboot sh /home/pi/exit.sh

Some of the code above has been gathered from around the web. –this link– shows how to exit all emulators too, however if done by this method, it is a hard exit because sigkill is used. This can cause all sorts of headaches like SRM’s not being saved, high scores not being saved using mame, etc… So I modified it to use sigterm. However, mame4all doesn’t accept sigterm signals and I certainly didn’t want to use a sigkill, so then I added uinput KEY_ESC to exit out of mame4all and it works.

The button works for me as intended. I set up a pushbutton attached to GPIO 3 on a Raspberry Pi 2 and it exits the emulator cleanly to emulationstation. Because I have it set to GPIO3, it also boots my Pi when it is shut off.

If there are any other questions, I’ll do my best to answer them.

[dougie1970]

thanks for the info and can you take a pic of how to add the button to the GPIO .

[matthewjosephcordova]

It’s simple, just connect from GPIO3 to ground using a push button type button. Look at your rpi documentation for the correct pins. On the rpi2 b+ they are right next to each other

[Anonymous]

thanks for sharing this.

i do not understand why gpio boots up your pi…what am i missing here?

[matthewjosephcordova]

It’s a largely undocumented feature using GPIO3 to boot a Pi. See http://elinux.org/RPI_safe_mode#cite_note-1
‘Wake from halt’

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