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This is a simple mouse emulator for Atari ST type of computers. Old Atari mouse can get broken and can be a pain to use. There are various hardware emulators for Atari mouse but none of them support a modern USB mouse (some probably do, but are a bit pricey or hard to get).

This started as a fun side project after watching Backoffice show video on using RPi to emulate Atari mouse. It was a proof of concept and I decided to make a POCv2. :)

How it's done?

RPi serves as a USB HID interface as an easy access to /dev/input/mice. Input is read, converted to proper signals for Atari ST and then sent out via GPIO to Atari ST. A seven wire cable with half a dozen resistors and a DB9 connector is all that you need for connecting these two.

What's missing?

Atari can't cope with the speed of modern USB mice that's why a lot of data has to be thrown away. Right now there's a hard limit on read and on input. In a nutshell, USB input needs to be converted into variable frequency pulses for Atari ST.

(And they aren't even pulses, just state changes.)

How to use it?

Unzip or untar or whatever you downloaded. If you're simply goofing out on a PC then you don't need anything else if you're on Raspberry Pi, then you need WiringPi libraries installed. You also need GCC compiler and cmake.


$ sudo apt install wiringpi
$ sudo apt install cmake

Build the STuffEmu

$ tar -xvzf stuffemu.tar.gz
$ cd STuffEmu
$ mkdir build
$ cd build
$ cmake ..
$ make

If everything compiled you can now run the program with ./stuffemu, rejoice! Don't worry if you did not connect your Atari to RPi nothing will blow up. If you did, it might.

If you move your mouse around, a mouse that is connected to the computer you're running STuffEmu on, a bunch of debug data will print in your terminal.

When you're done you can press CTRL-C to end stuffemu.

If you want a system wide installation and you want to start STuffEmu on startup you can run these commands:

$ sudo make install
$ sudo systemctl enable stuffemu.path
$ sudo systemctl start stuffemu.path

This will install stuffemu in /opt/stuffemu and all the systemd scripts in /lib/systemd/system then it will enable stuffemu at boot and start it. Your mouse should be working now and after a reboot.


If you're running stuffemu as user pi or root (and you probably should not run it as root) then everything should work. If you're running it as nother user then you'll have to take care of the necessary permissions for devices.

The easiest was for this is to edit the /etc/group file and add your username to the input and gpio group.

How to connect Atari ST with Raspberry PI?

Take DB9 female connector, solder 330 Ohm resistors on pins 1, 2, 3, 4, 6, 9. Attach some wires to the resistors and connect them to GPIO pins 0, 5, 6, 13, 19 and 26. Then also connect DB9 pin 8 to one of the GND pins on RPi. Joystick pinout is similar, see diagram below.

GPIO pins on RPI B+ are mapped on the GPIO header like this:


1 0 27
2 5 29
3 6 31
4 13 33
6 19 35
8 GND 39
9 26 37


1 25 22
2 8 24
3 7 26
4 1 28
6 16 36
8 GND 34

Wiring diagrams are in the doc directory. Stock DB9 connector in Fritzing was a little bit strange, so there's an alternative version and you'll probably need to import it if you want to open the .fzz file.


Rubber-band effect

High-DPI mice are inexpensive and ubiquitous; even Amazon's own-brand cordless mouse delivers a high DPI to the host machine. Unfortunately, the decision was made by the Raspberry Pi kernel developers to change the default mouse polling frequency to 60Hz. This works fine for ~15 year old mice but modern mice will not behave the same way: Mouse motion will appear laggy and elastic, and the pointer will continue to move even after your hand has stopped. This is even a problem with the Pi's default desktop environment.

This is not a fault with STuffEmu, which abstracts reading mouse motion from reporting to the computer in a way that copes with these DPI issues.

If you encounter this issue, you should likely increase your mouse polling rate. Whilst mousepoll is exposed via the /sys/module interface, it cannot be adjusted during normal operation and will require a reboot, so do not be surprised if adjusting it this way yields no results; a reboot is required.

Start by changing the mousepoll value to 0 in /boot/cmdline.txt. Add usbhid.mousepoll=0 to the end of the first line. DO NOT CREATE A SECOND LINE.

I own two Tecknet cordless mice whose motion remains laggy even after changing the mousepoll parameter to 0. In these cases, I set the mousepoll to 2 and the problem was corrected.

Reboot after making the change to /boot/cmdline.txt.

Please note that increasing the polling interval uses more CPU time. This was not found to be a problem on the Pi Zero but I have not tested with older 700MHz models.

It is possible that there is some connection between the bInterval variable in the USB information block for mouse HID devices, and that this value is the recommended value for your mousepoll parameter. For example, from my Tecknet mice:

      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x81  EP 1 IN
        bmAttributes            3
          Transfer Type            Interrupt
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0007  1x 7 bytes
        bInterval               2

However I am not familiar with the HID specification so cannot be certain.


Why not? My idea is to actually power Raspberry Pi from the Atari's power supply. Unfortunately 5V from Atari mouse/joy port isn't enough to power RPi2. It might be enough to power RPi Zero.

Final thoughts

I want an RPi in my Atari. It will emulate mouse, joystick and will provide an USB mount point for GoTEK floppy emulator running FlashFloppy.

Yes, I know about CosmosEx for Atari, but I don't need that much. Altho HDD emulation would be nice and I'll look into that. :)

Yes, I know that having a Raspberry Pi inside an Atari ST is an overkill and that RPi could easily emulate whole Atari ST, but I like my Atari.

Amiga support

STuffEmu is now also working on Amiga. It was tested on Amiga 600. You will have to use -a switch when running the program to turn on the Amiga mode. Amiga and Atari modes are incompatible so you can't have one stuffemu running for both computers.

Amiga hardware issues

The Amiga's right and middle mouse buttons intersect with the Y and X axis of analogue joystick inputs respectively owing to the ports being compatible with multiple types of input device, and are potentiometer inputs. In spite of the mouse-mode inputs being read digitally, if the voltage level is too low the Amiga-side CIA won't register the required "high" to trigger the input and it will be ignored.

As a result, if there is a 330 ohm resistor on pin 9, the right mouse button will not work. You might try with a smaller value resistor. I just removed it and it seems that everything is fine. Resistors on all the other pins aren't causing any problems.

The Amiga DB9 pin 7 is a 5V pin with a maximum load of 50mA which is not sufficient to power any form of Raspberry Pi.


Connecting various stuff and wires to your computer, let it be a new PC, small Raspberry Pi or an old Atari ST, can damage your computer. This thing works and it worked for me. It might not work for you. You're at your own here.


Atari ST / Amiga mouse emulator







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