mk_arcade_joystick_rpi

The Raspberry Pi GPIO Joystick Driver

The mk_arcade_joystick_rpi is fully integrated in the Batocera.linux distribution

Introduction

The Raspberry Pi is an amazing tool I discovered a month ago. The RetroPie project made me want to build my own Arcade Cabinet with simple arcade buttons and joysticks.

So i started to wire my joysticks and buttons to my raspberry pi, and I wrote the first half of this driver in order to wire my joysticks and buttons directly to the RPi GPIOs.

However, the Raspberry Pi Board B Rev 2 has a maximum of 21 usable GPIOs, not enough to wire all the 28 switches (2 joystick and 20 buttons) that a standard panel requires.

UPDATE 0.1.7 : Compatibility with rpi4 and some adjustments (Big thanks to @Gemba)

UPDATE 0.1.6 : Compilation with Kernel 4.15 and above fixed + find the BCM peripherals base address dynamically + Hotkey buttons added (Big thanks to @cmitu)

UPDATE 0.1.5 : Added GPIO customization

UPDATE 0.1.4 : Compatibility with rpi2 and rpi3

UPDATE 0.1.3 : Compatibility with 3.18.3 :

The driver installation now works with 3.18.3 kernel, distributed with the last firmware.

UPDATE 0.1.2 : Downgrade to 3.12.28+ :

As the module will not load with recent kernel and headers, we add the possibility of downgrading your firmware to a compatible version, until we find a fix.

UPDATE 0.1.1 : RPi B+ VERSION :

The new Raspberry Pi B+ Revision brought us 9 more GPIOs, so we are now able to connect 2 joysticks and 12 buttons directly to GPIOs. I updated the driver in order to support the 2 joysticks on GPIO configuration.

Even More Joysticks

A little cheap chip named MCP23017 allows you to add 16 external GPIO, and take only two GPIO on the RPi. The chip allows you to use GPIO as output or input, input is what we are looking for if we want even more joysticks.

If you want to use more than one chip, the i2c protocol lets you choose different addresses for the connected peripheral, but all use the same SDA and SCL GPIOs.

In theory you can connect up to 8 chips so 8 joystick.

The Software

The joystick driver is based on the gamecon_gpio_rpi driver by marqs

It is written for 4 directions joysticks and 8 buttons per player. Using a MCP23017 extends input numbers to 16 : 4 directions and 12 buttons.

It can read one joystick + buttons wired on RPi GPIOs (two on RPi B+ revision) and up to 5 other joysticks + buttons from MCP23017 chips. One MCP23017 is required for each joystick.

It uses internal pull-ups of RPi and of MCP23017, so all switches must be directly connected to its corresponding GPIO and to the ground.

Common Case : Joysticks connected to GPIOs

Pinout

Let's consider a 6 buttons cab panel with this button order :

 ↑   Ⓨ Ⓧ Ⓛ  
← →	 Ⓑ Ⓐ Ⓡ  
 ↓  

With R = TR and L = TL

Here is the rev B GPIO pinout summary :

If you have a Rev B+ RPi or RPi2/RPi3/RPi4:

Of course the ground can be common for all switches.

Loading the driver

The driver is loaded with the modprobe command and take one parameter nammed "map" representing connected joysticks. When you will have to load the driver you must pass a list of parameters that represent the list of connected Joysticks. The first parameter will be the joystick mapped to /dev/input/js0, the second to js1 etc..

If you have connected a joystick on RPi GPIOs (joystick 1 on the pinout image) you must pass "map=1" as a parameter. If you are on B+ revision and you connected 2 joysticks you must pass map="1,2" as a parameter.

If you have one joystick connected on your RPi B or B+ version you will have to run the following command :

sudo modprobe mk_arcade_joystick_rpi map=1

If you have two joysticks connected on your RPi B+ version you will have to run the following command :

sudo modprobe mk_arcade_joystick_rpi map=1,2

If you have a TFT screen connected on your RPi B+ you can't use all the gpios. You can run the following command for using only the gpios not used by the tft screen (Be careful, not all tft screen use the same pins. GPIOs used with this map: 21,13,26, 19,5,6,22,4,20,17,27,16):

sudo modprobe mk_arcade_joystick_rpi map=4

If you don't want to use all pins or wants a custom gpio map use:

sudo modprobe mk_arcade_joystick_rpi map=5 gpio=pin1,pin2,pin3,.....,pin12

Where pinx is the number of the gpio you want. There are 12 posible gpio with button order: Y-,Y+,X-,X+,start,select,a,b,tr,y,x,tl. Use -1 for unused pins. For example gpio=21,13,26,19,-1,-1,22,24,-1,-1,-1,-1 uses gpios 21,13,26,19 for axis and gpios 22 and 24 for A and B buttons, the rest of buttons are unused.

The GPIO joystick 1 events will be reported to the file "/dev/input/js0" and the GPIO joystick 2 events will be reported to "/dev/input/js1"

Auto load at startup

Open /etc/modules :

sudo nano /etc/modules

and add the line you use to load the driver :

mk_arcade_joystick_rpi

Then create the file /etc/modprobe.d/mk_arcade_joystick.conf :

sudo nano /etc/modprobe.d/mk_arcade_joystick.conf

and add the module configuration :

options mk_arcade_joystick_rpi map=1,2

Testing

Use the following command to test joysticks inputs :

jstest /dev/input/js0

More Joysticks case : MCP23017

Here is the MCP23017 pinout summary :

Preparation of the RPi for MCP23017###

Follow the standards installation instructions.

Activate i2c on your RPi :

sudo nano /etc/modules

Add the following lines in order to load i2c modules automatically :

i2c-bcm2708 
i2c-dev

And if the file /etc/modprobe.d/raspi-blacklist.conf exists :

sudo nano /etc/modprobe.d/raspi-blacklist.conf

Check if you have a line with :

i2c-bcm2708 

and add a # at the beginning of the line to remove the blacklisting

Reboot or load the two module :

modprobe i2c-bcm2708 i2c-dev

Preparation of the MCP23017 chip

You must set the pins A0 A1 and A2 to 0 or 1 in order to set the i2c address of the chip. If you only have 1 chip, connect the 3 pins to the ground. Just connect one of the pins to 3.3v to set its state to 1 and change the i2c address of the MCP23017.

You must also connect the RESET pin to 3.3v.

Configuration

When you want to load the driver you must pass a list of parameters that represent the list of connected Joysticks. The first parameter will be the joystick mapped to /dev/input/js0, the second to js1 etc..

If you have connected a joystick on RPi GPIOs you must pass "1" as a parameter.

If you have connected one or more joysticks with MCP23017, you must pass the address of I2C peripherals connected, which you can get with the command :

sudo i2cdetect -y 1

The configuration of each MCP23017 is done by setting pads A0 A1 and A2 to 0 or 1.

If you configured your MCP23017 with A0 A1 and A2 connected to the ground, the address returned by i2cdetect should be 0x20

So if you have a joystick connected to RPi GPIOs and a joystick on a MCP23017 with the address 0x20, in order to load the driver, you must run the command :

sudo modprobe mk_arcade_joystick_rpi map=1,0x20

The GPIO joystick events will be reported to the file "/dev/input/js0" and the mcp23017 joystick events will be reported to "/dev/input/js1"

I tested up to 3 joystick, one on GPIOs, one on a MCP23017 on address 0x20, one on a MCP23017 on address 0x24 :

sudo modprobe mk_arcade_joystick_rpi map=1,0x20,0x24

Credits

• gamecon_gpio_rpi by marqs
• RetroPie-Setup by petRockBlog
• Low Level Programming of the Raspberry Pi in C by Pieter-Jan
• For these numerous works to maintain this project by cmitu and Gemba
• All people who recognize themselves ♥