I have dreamed about building an arcade machine for some months already. I knew the amazing MAME project -- responsible to emulate most of the hardware found in old-school arcade machines -- and I wanted an embedded system that just runs that.
Looking around, I found great platforms like RetroPi, Lakka, and Recallbox. However, they target emulating many consoles (e.g., NES, SNES, Sega Megadrive, etc.) as well as arcade games via MAME. Unfortunately, the MAME version that they provide is rather old, for example, from 2006! I like the idea of just running MAME in my Raspberry Pi.
Luckily, I was not alone! I found the MAME appliance project that addresses this problem. It takes the Debian-based Raspbian OS and sets it up in a way that you can have your Raspberry Pi up to date with the latest version of MAME. The project is also set up to be minimalist in the amount of resources that it uses, e.g., it does not utilize X11. The project provides a 12 GB SD card image with the latest MAME version in it.
After studying the project for some time. I introduced three modifications to fit my needs.
The MAP works in two modes: servicemode and arcademode. Service mode enables
arcade maintainers to perform activities like login into the system via SSH or a
terminal, transfer files, etc. In contrast, arcade mode dedicates
all the resources to play games.
One of the complications I found with MAP was transitioning from arcademode
into servicemode -- something that can demand to take out the SD card from the
Raspberry Pi to delete some files.
My proposal is that the system always runs in arcademode but if you press a
bottom and/or move the joystick at boot time, then the system goes into
servicemode.
First, we need an
script
that detects if the joystick (the one in /dev/input/js0) has moved or a button
has been pressed.
#/bin/bash
#file: /home/pi/scripts/mame-joystick-detect.sh
# Testing joystick movement or buttons
JOY0=/dev/input/js0
# Waiting for some input
timeout 5s jstest --event ${JOY0} > /tmp/joystick0
# Checking if some input has occured
INPUT=$(grep -e "type 1," -e "type 2," /tmp/joystick0 | wc -l)
if [ $INPUT -eq 0 ]; then
touch /tmp/arcademode-confirm
exit 0 # input not-detected!
fiThe script waits five seconds for inputs from either a joystick movement (type 1 event) or a pressed button (type 2 event). If no input gets detected,
then the script creates the empty file /tmp/arcademode-confirm. We will see
the utility of this file later on.
We also create a systemd service to run this script at runtime.
[Unit]
Description=Reading input from joystick
[Service]
Type=oneshot
ExecStart=/bin/bash /home/pi/scripts/mame-joystick-detect.sh
[Install]
WantedBy=multi-user.target
Now, we need to modify the service responsible to launch MAME (file mame-autostart.service) from this:
[Unit]
Description=MAME Appliance Autostart service
Conflicts=getty@tty1.service smbd.service nmbd.service rng-tools.service cron.service mame-artwork-mgmt.service
Requires=local-fs.target
After=local-fs.target
[Service]
User=pi
Group=pi
PAMName=login
Type=simple
ExecStart=/home/pi/scripts/autostart.sh
Restart=on-abort
RestartSec=5
TTYPath=/dev/tty1
StandardInput=tty
[Install]
WantedBy=multi-user.target
Also=shutdown.service
[Unit]
Description=MAME Appliance Autostart service
After=mame-question.service
ConditionPathExists=/tmp/arcademode-confirm
Conflicts=getty@tty1.service smbd.service nmbd.service rng-tools.service cron.service mame-artwork-mgmt.service
[Service]
User=pi
Group=pi
PAMName=login
Type=simple
EnvironmentFile=/etc/environment
ExecStart=/home/pi/scripts/autostart.sh
Restart=on-abort
RestartSec=5
TTYPath=/dev/tty1
StandardInput=tty
[Install]
WantedBy=multi-user.target
Also=shutdown.service
The modifications include
- considering launching this service after asking for joysticks' inputs (see line
After=mame-question.service), and - launching MAME only under the existence of the file
/tmp/arcademode-confirm(see lineConditionPathExists=/tmp/arcademode-confirm) -- recall that such file will exist only if there were no joysticks' inputs!
So, if there are no joysticks' inputs, then MAME will execute by calling
/home/pi/scripts/autostart.sh. Otherwise, all the services declared as
conflicting above are successfully launched, which will allow users to login
into the system as in servicemode.
I plan to have my arcade in my office. So, having an arcade with noise all the time might disturb the working environment. In this light, I propose another modification which consists on adding a button to the Raspberry Pi (GPIO-based interface) to lower the volume, mute, and unmute the sound. In that manner, the arcade can show gameplays but without disturbing your work mates. People that want to play, however, can just unmute and enjoy the arcade from time to time.
The goal is that if you keep pressing the button for some seconds (no more than 5), you will hear that the volume is changed to a minimum. Then, if you keep pressing the button again for some seconds, the arcade will mute. Finally, if you keep pressing the button, you will see that the arcade unmutes and its volume is high.
The hardware that you need is simply a push switch -- I followed most of the idea from this post. You need to connect two cables into the push switch: one into the GPIO 4 (look for pin 4 in your board) and another into ground (look for GND in your board). You can change the GPIO 4 for whatever GPIO available you have on the board.
We start by writing an script to change the volume when detecting (every five seconds) that the button has been pressed.
#!/bin/bash
#file:/home/pi/scripts/mame-vol.sh
HIGH="95%"
LOW="70%"
MUTE="0%"
BREAK=5
# Initialize GPIO pin
echo 4 > /sys/class/gpio/unexport # Deactivate GPIO 4
echo 4 > /sys/class/gpio/export # Activate GPIO 4
#echo in > /sys/class/gpio/gpio4/direction # Input signal
amixer cset numid=1 $HIGH
while true; do
read SIGNAL < /sys/class/gpio/gpio4/value
# If the signals are different, the button was pressed
if [ $SIGNAL -eq 0 ]; then
echo "Volume button pressed"
CHECK_VOL=$(amixer | grep Mono: | awk -F"[\[\]]" '{print $2}')
echo "Current volume:" $CHECK_VOL
case $CHECK_VOL in
$HIGH)
echo Setting volume to low
amixer cset numid=1 $LOW ;;
$LOW)
echo Setting volume to mute
amixer cset numid=1 '$MUTE' ;;
$MUTE)
echo Setting volume to high
amixer cset numid=1 $HIGH ;;
*)
amixer cset numid=1 $HIGH ;;
esac
fi
sleep $BREAK
doneWe also write a systemd service to launch this script only in
arcademode.
[Unit]
Description=Controlling volume for MAME with a button
After=mame-question.service
ConditionPathExists=/tmp/arcademode-confirm
[Service]
User=pi
Group=pi
ExecStart=/bin/bash /home/pi/scripts/mame-vol.sh
[Install]
WantedBy=multi-user.target
Observe that the script is run only if no joysticks' inputs are detected (see
After=mame-question.service and
ConditionPathExists=/tmp/arcademode-confirm).
It is useful to know the IP of your MAP when entering into
servicemode. So, I propose to modify the file /etc/issue:
Raspbian GNU/Linux 10 \n \l
S E R V I C E M O D E
IP: \4{eth0}
Here I write some possible extensions and or aspects that I would like to explore further with MAP.
- So far, the joysticks' input come from
/dev/input/js0, but why not generalize this to consider any joystick in the system? - It is not clear when exactly at boot time the script is waiting for the joystick's input. At this point, when you see the MAME splash screen, you should start moving the joystick or pressing a button. While this works, it would be nice to play some sound to indicate exactly when the input is expected.
- Make sure that when in
arcademode, all network is down -- this is not the case right now. For instance, we havewpa_supplicantservice up. - The patch does not work for MAME 0238. The lines where the patch is applied
has been changed, and you need to do the patching manually. So,
mame-updater.shneeds to be changed and a new patch file needs to be created for MAME 0238. What about 0239? - How do we automatically deploy any further modifications of scripts? I am planning building many MAPs :)